Methods for high quality boron arsenide single crystal growth

Abstract

Methods for producing a single crystal boron arsenide, and single crystal boron arsenide produced by the methods are disclosed. In one aspect, the method includes contacting elemental boron with elemental arsenic to form a reaction mixture; maintaining the reaction mixture at a temperature above melting point of arsenic for an effective amount of time to form a product mixture comprising the single crystal boron arsenide and liquid arsenic; cooling the product mixture for a predetermined amount of time; and separating the liquid arsenic from the single crystal boron arsenide.

Description

METHODS FOR HIGH QUALITY BORON ARSENIDE SINGLE CRYSTAL GROWTHCROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 586,851 filed September 29, 2023, and titled "METHODS FOR HIGH QUALITY BORON ARSENIDE SINGLE CRYSTAL GROWTH" the entirety of which is incorporated herein by reference.ACKNOWLEDGEMENT OF GOVERNMENT SUPPORT

[0002] This invention was made with government support under Grant No. N00014-22-1- 2755 awarded by the Office of Naval Research and Grant No. 2329110 awarded by the National Science Foundation. The government has certain rights in the invention.BACKGROUND

[0003] 1. Field

[0004] The present disclosure relates generally to methods for producing a single crystal boron arsenide, single crystal boron arsenide produced by the methods, and composition containing the single crystal boron arsenide. In one aspect, the method to produce a single crystal boron arsenide can include a melt growth method. In another aspect, the method for producing a single crystal boron arsenide can include a Bridgman growth method.

[0005] 2. Discussion of Related Art

[0006] Thermal management stands as a paramount challenge in modem technology, especially in the realm of modem electronics. The evolution of technology over the past half- century, including the progressive miniaturization of transistors, intricate compactness, and novel fabrication methodologies, has resulted in the creation of high-density power electronic and optoelectronic integrated circuits. These advancements have yielded circuits that are not only smaller, faster, and more powerful, but also inevitably generate a significant amount of heat. For instance, the data storage center consumes over 200 TWH of electricity annually and more than half of the total energy is used for cooling. The semiconductor industry also faces a significant technological challenge due to the presence of elevated hot-spot temperature, which precipitates the degradation of device performance. In response to these issues, scientists have demoted decades to the exploration of alternation materials with enhanced thermal conductivity. tn 1972. GA Slack gave four rules of finding crystals with high thermal conductivity: low atomic mass, strong bonding, simple crystal structure, and low anharmonicity [1]. Among these tenets, diamond emerges and show the highest thermalconductivity (κ) of around 2200 Wm-1K-1. However, it’s application remains constrained due to the steep cost, size limitation, and intricate synthesis which needs an environment of high pressure and high temperature Graphite, another carbon based high thermal conducting materials, shows conductivity of about 1900 Wm-1K-1in the in-plane direction [3, 4), Nevertheless, its metallic behavior renders it less suitable for widespread electronic applications. Cubic boron nitride showing high thermal conductivity of about 1600 Wm-1K-1at room temperature [5], requires an elaborate synthetic condition including pressures exceeding 10 GPa and temperature surpassing 2000 °C. It also suffers limitations related to size, yield efficiency, and cost considerations.

[0007] Recently, unusual high thermal conductivity values, exceeding 1000 Wm-1K-1at room temperature, have been predicted by first-prindples calculations and subsequently experimentally validated in semiconducting c-BAs, which surpasses the conductivity benchmarks set by industrial standards such as SIC and copper by more than three times [6], Such high thermal conductivity of BAs has been attributed to the combination of a large frequency gap between the acoustic and optical phonons, and the bundling of the acoustic phonon dispersions caused by the unique mass ratio of constituent atoms. Moreover, BAs has a better thermal expansion coefficient (CTE) match with silicon and other Ill-V semiconductors than diamond [7, 8] and comparable mechanical properties with other common semiconductors [9, 10], The thermal boundary conductance of GaN structures on BAs has been measured to be 250 MW m-2K-1, higher than that for diamond [11-13]. Due to the high optical phonon energy, furthermore, simultaneously high hole and electron mobilities (2110 cm2V-1s and 1400 cm2V-1s , respectively) at room temperature

[0014] in c-BAs have been predicted by first principles calculations and revealed by high-resolution measurements of low- defect regions of c-BAs crystals [15, 16] .

[0008] However, it remains a significant challenge to use the chemical vapor transport (CVT) method to obtain c-BAs crystals with low and uniform defect concentration and a size larger than millimeter. The nature of spontaneous nucleation from the vapor phase supersaturation during the CVT process often yields small and clustered crystals from the unpredictable nudeation Sites, Moreover, the difficulty in controlling unintentional impurity doping in CVT growth results in low bulk thermal conductivities and inconsistent electrical resistivity behavior in the grown crystals [17-19). c-BAs crystals obtained by CVT often exhibits a p-type conductivity with a hole concentration above 1018cm-3and up to 1020cm-3[17, 19} due to either unintentional carbon or silicon substitutional impurity doping, vacancies, voids, or anti- site defects at the As site. [17, 20-22].

[0009] ft is with these observations in mind, among others, that various aspects of the present disclosure were conceived and developed.SUMMARY

[0010] Various embodiments of the disclosure are discussed in detail below. While specific implementations are discussed, it should be understood that this is done for illustration purposes only. A person skilled in the relevant art will recognize that other components and configurations may be used without parting from the spirit and scope of the disclosure.[0011) A discovery has been made that provides a solution to at least one or more of the aforementioned problems associated with single crystal boron arsenide. In one aspect, a melt growth, such as a flux growth method to produce a single crystal boron arsenide is provided. In another aspect, a Bridgman growth method to produce a single crystal boron arsenide is provided. The melt growth and Bridgman growth methods are scalable. The single crystal boron arsenide made by the melt growth or Bridgman growth method can have one or more properties that are not found in single crystal boron arsenide made by CVT method.

[0012] Some aspects of the disclosure are directed to a method to produce a single crystal boron arsenide. In one aspect, a melt growth, such as a flux growth method to produce a single crystal boron arsenide is described. The melt growth, such as the flux growth method cah include contacting elemental boron With elemental arsenic to form a reaction mixture; keeping or maintaining the reaction mixture at a temperature above the melting point of arsenic for an effective amount of time to form a product mixture containing the single crystal boron arsenide and liquid arsenic; cooling the product mixture for a desired or predetermined amount of time; and separating the liquid arsenic from the single crystal boron arsenide. The melting point of arsenic can be the melting point of arsenic at atmospheric pressure. The single crystal boron arsenide can contain a single crystal of boron arsenide. The single crystal boron arsenide formed can have a cubic crystal structure. In certain embodiments, the single crystal boron arsenide formed has a face centered zinc blende structure.

[0013] In certain embodiments, the reaction mixture is kept at a temperature 820 °C to 920 °C to form the product mixture. In certain embodiments, the reaction mixture is kept at a temperature 840 °C to 900 °C to form the product mixture. In certain particular embodiments, the reaction mixture is kept at a temperature 820 °C to 920 °C: 840 °C to 920 °C; 820 °C to 900 °C; 840 °C to 900 °C; 820 °C; 830 °C; 840 °C; 850 °C; 860 °C; 870 °C; 880 °C; 890 °C; 900 °C; 910 °C or 920 °C or any range of value therebetween, to form the product mixture.

[0014] The elemental boron and elemental arsenic can be contacted at a boron:arsenic molar ratio of 1 :1 to 1 :10 to form the reaction mixture. In certain embodiments, the elemental boron and elemental arsenic is contacted at a boron:arsenic molar ratio of 1:4 to 1:10 to form the reaction mixture. In certain particular embodiments, the elemental boron and elemental arsenic is contacted at a boron:arsenic molar ratio of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9,or 1:10. or any range of value therebetween, to form the reaction mixture. The elemental boron and elemental arsenic can be contacted at an oxygen level less than 1 ppm, and / or a moisture level less than 1 ppm. In certain embodiments, the elemental boron and elemental arsenic is contacted at an i) oxygen level < 1 ppm to 0.1 ppm; < 1 ppm to 0.01 ppm; < 1 ppm to 0.001 ppm; or <1 ppm to 0.0001 ppm; and / or a moisture level < 1 ppm to 0.1 ppm; < 1 ppm to 0.01 ppm; < 1 ppm to 0.001 ppm; or <1 ppm to 0.0001 ppm.

[0015] In certain embodiments, the elemental boron contains crystalline boron, amorphous boron or both. In certain particular embodiments, the elemental boron contains crystalline boron. The elemental boron can have a purity greater than 99%. In certain embodiments, the elemental boron has a purity > 99%; > 99.5 %; > 99.9 %; > 99.99 %; > 99.999 %; > 99% to 99.9999%; > 99.5 % to 99.9999%; > 99.9 % to 99.9999%; > 99.99 % to 99.9999%; or > 99.999 % to 99.9999%.

[0016] The elemental arsenic can have a purity greater than 99%. In certain embodiments, the elemental arsenic has a purity > 99%; > 99.5 %; > 99.9 %; > 99.99 %; > 99.999 %; > 99% to 99.9999%; > 99.5 % to 99.9999%; > 99.9 % to 99.9999%; > 99.99 % to 99.9999%; or > 99.999 % to 99.9999%. The elemental arsenic can contain an arsenic chunk.

[0017] Impurity level in the reaction mixture can be less than 1 ppm. In certain embodiments, the impurity level in the reaction mixture is less than 0.1 ppm. In certain embodiments, the impurity level in the reaction mixture is less than 0.01 ppm. In certain embodiments, the impurity level in the reaction mixture is < 0.1 ppm to 0.001 ppm; <0.1 ppm to 0.0001 ppm; <0.1 ppm to 0.00001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; or <0.01 ppm to 0.00001 ppm. Impurity level in the reaction mixture can be the impurity level prior to heating the reaction mixture above the melting point of arsenic.

[0018] The elemental boron and elemental arsenic can be contacted in a reaction vessel, and the reaction mixture can be formed in the reaction vessel. The gas from the reaction vessel containing the reaction mixture can be evacuated with a pressure less than 10- 5Pa, and the reaction vessel can be sealed. The sealed reaction vessel can be heated to the temperature above the melting point of arsenic, such as to 820 °C to 920 °C, and kept for the effective amount Of time to form the product mixture. The reaction mixture in the reaction vessel can be kept at a pressure less than 10-5Pa to 107Pa, at the temperature 820 °C to 920 °C for the effective amount of time to form the product mixture. The effective amount of time can be 1 week or more. In certain embodiments, the effective amount of time is 1 week to 3 week. In certain particular embodiments, the effective amount of time is 7 days to 21 days; 7 days to 14 days; 7 days; 9 days; 11 days; 13 days; 15 days; 17 days; 19 days; or 21 days, or any range or value therebetween.

[0019] The impurity level in the reaction vessel can be less than 1 ppm. In certain embodiments, the impurity level in the reaction vessel is less than 0.1 ppm. In certain embodiments, the impurity level in the reaction vessel is less than 0.01 ppm. In certain embodiments, the impurity level in the reaction vessel is < 0.1 ppm to 0.001 ppm; <0.1 ppm to 0.0001 ppm; <0.1 ppm to 0.00001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; or <0.01 ppm to 0.00001 ppm. The impurity level in the reaction vessel can be the impurity level prior to contacting the elemental boron, and elemental arsenic in the reaction vessel. In certain embodiments, the reaction vessel is a quarto vessel, such as a quarto tube. In certain embodiments, the quartz vessel is washed with hydrofluoric acid, rinsed with isopropyl alcohol, and dried prior to contacting the elemental boron, and elemental arsenic in the quartz vessel.

[0020] The product mixture can be cooled to 780 " or below, In certain embodiments, the product mixture is cooled to 750 °C to 780 °C; 750 °C; 760 °C: 770 °C; or 780 °C; or any range or value therebetween. The product mixture can be cooled slowly. In certain embodiments, product mixture is cooled at a rate at 0.5 to 1.5 °C / hour. In certain embodiments, product mixture to cooled at a rate of 0.1 to 2 °C / hour, 0.5 to 1.5 °C / hour, 0,1 °C / hour, 0.5 °C / hour; 1 °C / hour, 1.5 °C / hour, or 2 °C / hour; or any range or value therebetween.

[0021] The liquid arsenic can be separated from the single crystal boron arsenide using a suitable method, including but not limited to using a temperature gradient, centrifuge, or the like. In certain embodiments, the liquid arsenic is separated from the single crystal boron arsenide by establishing a temperature gradient in the product mixture. In certain embodiments, the temperature gradient in the product mixture is established by keeping or maintaining a first end of the product mixture at a first temperature, and a second end of the product mixture at a second temperature, wherein the second end can be an opposite end of the first end, and the second temperature can be lower than the first temperature. In certain embodiments, the first temperature is 700 to 800 °C The second temperature can be 700 °C or below. In certain embodiments, the second temperature is 600 to 700 °C

[0022] In another aspect, a Bridgman growth method to produce a single crystal boron arsenide is described. The Bridgman growth method includes providing a reaction vessel with or without a boron arsenide crystal seeding crystal ; providing elemental boron, and elemental arsenic to the reaction vessel to form a reaction mixture in the reaction vessel; changing a temperature of the reaction mixture from a first temperature to a second temperature, from the second temperature to a third temperature, from the third temperature to the second temperature, and from the second temperature to the first temperature to form a product mixture containing a single crystal boron arsenide and liquid arsenic; and separating the liquid arsenic from the single crystal boron arsenide. In certain embodiments, the reaction vesselcontains the boron arsenide crystal seeding crystal. The reaction mixture can be in contact with the boron arsenide crystal seeding crystal. In certain embodiments, the gas from the reaction vessel containing the reaction mixture can be evacuated with a pressure less than 10-5pascal (Pa), and the reaction vessel can be sealed, and the temperature of the reaction mixture can be changed in the sealed reaction vessel. The temperature of the reaction mixture can be changed at a pressure less than 10-5Pa to 107Pa. The single crystal boron arsenide can contain a single crystal of boron arsenide. The single crystal boron arsenide formed can have a cubic crystal structure. In certain embodiments, the single crystal boron arsenide formed has a face centered zinc blende structure.

[0023] The second temperature can be higher than the first temperature, and the third temperature. The third temperature and the first temperature can be the same or different. In certain embodiments, the first temperature is 820 to 860 °C. In certain embodiments, the first temperature is 830 °C to 860 °C In certain particular embodiments, the first temperature is 820 °C, 830 °C, 840 °C, 850 °C or 830 °C, or any range or value therebetween, in certain embodiments, the second temperature is 860 °C to 900 °C. In certain particular embodiments, the second temperature is 860 °C, 870 °C, 880 °C, 890 °C or 900 °C, or any range or value therebetween. In certain embodiments, the third temperature is 820 °C to 860 °C. In certain embodiments, the third temperature is 820 °C to 860 °C. In certain embodiments, the third temperature is 830 °C to 860 °C. In certain particular embodiments, the third temperature is 820 °C, 830 °C, 840 °C. 850 °C or 830 °C , or any range or value therebetween. In certain embodiments, changing the temperature of the reaction mixture from the first temperature to the second temperature, from the second temperature to the third temperature, from the third temperature to the second temperature, and then from the second temperature to the first temperature, is repeated, such as at least 2 times, at least 3 times, at least 4 times, at least 5 times, at least 6 times, at least 7 times, at least 8 times, at least 9 times, at least 10 times, at least 15 times, at least 20 times, 2 to 20 times, 2 to 10 times, 2 times, 4 times, 6 times, 8 times, 10 times, 12 times, 14 times, 16 times, 18 times, or 20 times, or any range or value therebetween.

[0024] The temperature of the reaction mixture can be changed by moving the reaction vessel containing the reaction mixture, from a first temperature zone to a second temperature zone, from the second temperature zone to a third temperature zone, from the third temperature zone to the second temperature zone, and from the second temperature zone to the first temperature zone. In certain embodiments, the first temperature zone has a temperature of 820 °C to 860 °C. In certain embodiments, the first temperature zone has a temperature of 830 °C to 860 °C. In certain particular embodiments, the first temperature zone has a temperature of 820 °C, 830 °C, 840 °C, 850 °C or 830 °C or any range or valuetherebetween. In certain embodiments, the second temperature zone has a temperature of 860 °C to 900 °C. in certain particular embodiments, the second temperature zone has a temperature of 860 °C 870 °C, 880 890 °C or 900 °C, or any range or value therebetween, in certain embodiments, the third temperature zone has a temperature of 820 to 860 °C. In certain embodiments, the third temperature zone has a temperature of 830 °C to 860 °C. In certain particular embodiments, the third temperature zone has a temperature of 820 °C, 830 °C, 840 °C, 850 °C or 830 °C, or any range or value therebetween.

[0025] The first, second, and third temperature zones can be formed in a furnace. In certain embodiments, the furnace can be a Bridgman furnace. In the furnace, such as the Bridgman furnace the second temperature zone can be formed over the first temperature zone, and the third temperature zone can be formed over the second temperature zone.

[0026] The reaction vessel containing the reaction mixture can be moved between the temperature zones at 0.02 to 0.1 millimeter / second (mm / sec); 0.02 mm / sec; 0.03 mm / sec; 0.04 mm / sec; 0,05 mm / sec; 0.06 mm / sec; 0.07 mm / sec; 0.08 mm / sec; 0.09 mm / sec; or 0.1 mm / sec, or any range or value therebetween. The reaction vessel containing the reaction mixture can be rotated at 1 to 10 rotations per minute (rpm); 2 to 10 rpm; 3 to 10 rpm; 3 rpm; 4 rpm; 5 rpm; 6 rpm; 7 rpm; 8 rpm; 9 rpm; or 10 rpm, or any range or value therebetween while moving between the temperature zones. The rotation can be clockwise or counter clockwise, !n certain embodiments, direction of the rotation of the reaction mixture while moving between the temperature zones can be changed. As a non-limiting illustrative example the reaction mixture can be rotated clockwise white the temperature of the reaction mixture is changed from the first to second to third temperature, and rotated counter clockwise while the temperature of the reaction mixture is changed from the third to second to first temperature.

[0027] It would be evident to people of ordinary skill in the art teat the movement of the reaction vessel between the temperature zones can also be achieved by keeping the reaction vessel steady and moving the temperature zones with respect to the reaction vessel, or moving both the reaction vessel and the temperature zones with respect to each other. In certain embodiments, the temperature of the reaction mixture can be changed by a heater capable of cycling the temperature of the reaction mixture between the first second, and third temperatures. In certain embodiments, the third temperature and the first temperature are the same, and the reaction mixture is moved, such as cycled between the first temperature zone and the second temperature zone, and / or the third temperature zone is not formed.

[0028] The elemental boron and elemental arsenic can be provided to the reaction vessel at a boron:arsenic molar ratio of 1:1 to 1:10 to form the reaction mixture. In certain embodiments, the elemental boron and elemental arsenic is provided to the reaction vessel ata boron:arsenic molar ratio of 1 :4 to 1:10 to form the reaction mixture. In certain particular embodiments, the elemental arsenic is provided to the reaction vessel at a boron:arsenic molar ratio of 1:1, 1:2, 1:3, 1:4, 1:5, 1:6, 1:7, 1:8, 1:9, 1:10,or any range Of value therebetween, to form the reaction mixture. The elemental boron and elemental arsenic can be contacted at an oxygen level thes than 1 ppm, and / or a moisture level less than 1 ppm. The oxygen level in the reaction vessel can be < 1 ppm to 0.1 ppm; < 1 ppm to 0.01 ppm; < 1 ppm to 0.001 ppm; or <1 ppm to 0.0001 ppm; and / or the moisture level in the reaction vessel can be < 1 ppm to 0.1 ppm; < 1 ppm to 0.01 ppm; < 1 ppm to 0.001 ppm; or <1 ppm to 0.0001 ppm.

[0029] In certain embodiments, the elemental boron contains crystalline boron, amorphous boron or both. In certain embodiments, the elemental boron contains crystalline boron. The elemental boron can have a purity greater than 99%. In certain embodiments, the elemental boron has a purity > 99%; > 99.5 %; > 99.9 %; > 99.99 %; > 99.999 %; > 99% to 99.9999%; > 99.5 % to 99.9999%; > 99.9 % to 99.9999%; > 99.99 % to 99.9999%; or > 99.999 % to 99.9999%.

[0030] The elemental arsenic can have a purity greater than 99%. tn certain embodiments, the elemental arsenic has a purity > 99%; > 99.5%; > 99,9 %; > 99.99%; > 99.999 %; > 99% to 99.9999%; > 99.5 % to 99.9999%; > 99.9 % to 99.9999%; > 99.99 % to 99.9999%; or > 99.999 % to 99.9999%. The elemental arsenic can contain an arsenic chunk.

[0031] Impurity level in the reaction mixture can be less than 1 ppm. In certain embodiments, the impurity level in the reaction mixture is less than 0.1 ppm. In certain embodiments, the impurity level in the reaction mixture is less than 0.01 ppm. In certain embodiments, the impurity level in the reaction mixture is < 0.1 ppm to 0.001 ppm; <0.1 ppm to 0.0001 ppm; <0.1 ppm to 0.00001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; or <0.01 ppm to 0.00001 ppm. Impurity level in the reaction mixture can be the impurity level prior to heating the reaction mixture to the first temperature.

[0032] The impurity level in the reaction vessel can be less than 1 ppm. In certain embodiments, the impurity level in the reaction vessel is less than 0.1 ppm. In certain embodiments, the impurity level in the reaction vessel is less than 0.01 ppm. In certain embodiments, the impurity level in the reaction vessel is < 0.1 ppm to 0.001 ppm; <0.1 ppm to 0.0001 ppm; <0.1 ppm to 0.00001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; or <0,01 ppm to 0.00001 ppm. The impurity level in the reaction vessel can be the impurity level prior to providing the elemental boron, and elemental arsenic to the reaction vessel In certain embodiments, rite reaction vessel is a quartz vessel, such as a quartz tube. In certain embodiments, the quartz vessel is washed with hydrofluoric acid, rinsed withisopropyl alcohol, and dried prior to providing the elemental boron, and elemental arsenic to the quartz vessel.

[0033] The liquid arsenic can be separated from the single crystal boron arsenide using a suitable method, including but not limited to using a temperature gradient, centrifuge, or the like, in certain embodiments, the liquid arsenic is separated from the single crystal boron arsenide by establishing a temperature gradient in the product mixture. The temperature gradient in the product mixture can be established by keeping or maintaining a first end of the product mixture at a fourth temperature, and a second end of the product mixture at a fifth temperature, where the second end is an opposite end of the first end, and the fifth temperature is lower than the fourth temperature. In certain embodiments. the fourth temperature is 700 to 800 °C. The fifth temperature can be 100 °C or below. In certain embodiments, the fifth temperature is @00 to 700 °C.

[0034] Certain aspects are directed to a single crystal boron arsenide. The single crystal boron arsenide can contain a single crystal of boron arsenide. In certain embodiments, the single crystal boron arsenide is prepared by the melt growth. such as the fiux growth method, In certain embodiments, the single crystal boron arsenide is prepared by the Bridgman growth method. The single crystal boron arsenide formed can have a cubic crystal structure. In certain embodiments, the single crystal boron arsenide formed has a face centered zinc blende structure, in certain embodiments, the crystal boron arsenide is not formed by a chemical vapor transport method.

[0035] The single crystal boron arsenide can have at least one dimension greater than 1 millimeter (mm). In certain embodiments, the single crystal boron arsenide has at least one dimension greater than 2 millimeters (mms). In certain embodiments, the single crystal boron arsenide has at least one dimension 1 mm to 25.5 mms. In certain embodiments, the single crystal boron arsenide has at least one dimension 2 mms to 25.5 mms. In certain embodiments, the single crystal boron arsenide has at least one dimension 1 mm to 3 mms, 1 mm to 4 mms, 1 mm to 5 mms, 1 mm to 6 mms, 1 mm to 8 mms, 1 mm to 10 mms, 1 mm to 12 mms, 1 mm to 15 mms, 1 mm to 20 mms; 1 mm to 22 mms, 1 mm to 25.5 mms, 2 mms to 3 mms, 2 mms to 4 mms, 2 mms to 5 mms, 2 mms to 6 mms, 2 mms to 8 mms, 2 mms to 10 mms, 2 mms to 12 mms, 2 mms to 15 mms, 2 mms to 20 mms, 2 mms to 22 mms, 2 mms to 25.5 mms, 3 mms to 4 mms, 3 mms to 5 mms, 3 mms to 6 mms, 3 mms to 8 mms, 3 mms to 10 mms, 3 mms to 12 mms, 3 mms to 15 mms, 3 mms to 20 mms, 3 mms to 22 mms, 3 mms to 25.5 mms, 4 mms to 5 mms, 4 mms to 6 mms, 4 mms to 8 mms, 4 mms to 10 mms, 4 mms to 12 mms, 4 mms to 15 mms, 4 mms to 20 mms, 4 mms to 22 mms, 4 mms to 25.5 mms, 5 mms to 6 mms, 5 mms to 8 mms, 5 mms to 10 mms, 5 mms to 12 mms, 5 mms to 15 mms, 5 mms to 20 mms, 5 mms to 22 mms, 5 mms to 25.5 mms, 6 mms to 8 mms, 6 mms to 10 mms,6 mms to 12 mms, 6 mms to 15 mms, 6 mms to 20 mms, 6 mms to 22 mms, 6 mms to 25.5 mms, 8 mms to 10 mms, 8 mms to 12 mms, 8 mms to 15 mms, 8 mms to 20 mms, 8 mms to 22 mms, 8 mms to 25.5 mms, 10 mms to 12 mms, 10 mms to 15 mms, 10 mms to 20 mms, 10 mms to 22 mms, 10 mms to 25.5 mms, 12 mms to 15 mms, 12 mms to 20 mms, 12 mms to 22 mms, 12 mms to 25.5 mms, 15 mms to 20 mms, 15 mms to 22 mms, 15 mms to 25.5 mms, 20 mms to 22 mms, 20 mms to 25.5 mms, or 22 mms to 25.5 mms. In certain embodiments, the single crystal boron arsenide has at least one dimension 2 mms, 3 mms, 4 mms, 5 mms, 6 mms, 8 mms, 10 mms, 12 mms, 15 mms, 20 mms, 22 mms, or 25.5 mms. In Certain embodiments, the single crystal boron arsenide has at least one dimension at least 2 mms, 3 mms, 4 mms, 5 mms, 6 mms, 8 mms, 10 mms, 12 mms, 15 mms, 20 mms, or 22 mms. The at least one dimension can be a length, width, height, or diagonal of the single crystal. In certain embodiments, the at least one dimension is the distance between two points that are on a straight line and are on the surface of the single crystal The points can be on the same crystal surface, such as two furthest point on the same surface, or on different surfaces.[0036) The single crystal boron arsenide can contain a carrier concentration less than 1018 / centimeter3(cm3), preferably less than 1017 / cm3. In certain embodiments, the single crystal boron arsenide contains a carrier concentration of 1012 / cm3to < 1018 / cm3; 1013 / cm3to < 1018 / cm3; 1014 / cm3to < 1018 / cm3; 1015 / cm3to < 1018 / cm3; 1016 / cm3to < 1018 / cm3; 1017 / cm3to < 1018 / cm3; 1012 / cm3to 1017 / cm3; 1013 / cm3to 1017 / cm3; 1014 / cm3to 1017 / cm3; 1015 / cm3to 1017 / cm3; 1012 / cm3to 1016 / cm3; 1013 / cm3to 1016 / cm3; 1014 / cm3to 1018 / cm3; 1015 / cm3to 1018 / cm3; 1012 / cm3to 1015 / cm3; 1013 / cm3to 1015 / cm3; 1014 / cm3to 1015 / cm3; 1015 / cm3to 1018 / cm3; 1012 / cm3; 1013 / cm3; 1014 / cm3; 1015 / cm3; 1018 / cm3; 1017 / cm3; or < 1018 / cm3, or any range or value therebetween. The carrier concentration can be the carrier concentration in the single crystal boron arsenide prior to chemical doping. The carrier concentration values mentioned in this paragraph can be the carrier concentration values of the single crystal boron arsenide at room temperature, and can be measured using a method described in the examples, such as a Hall method.

[0037] The single crystal boron arsenide can have a thermal conductivity greater than 1000 Watts per meter Kelvin (W / m / K). In certain embodiments, the single crystal boron arsenide have a thermal conductivity of > 1000 W / m / K to 3000 W / m / K; > 1000 W / m / K to 2500 W / m / K;> 1000 W / m / K to 2000 W / m / K; > 1000 W / m / K to 1800 W / m / K; > 1000 W / m / K to 1600 W / m / K;> 1000 W / m / K to 1400 W / m / K; > 1000 W / m / K to 1200 W / m / K; 1100 W / m / K to 3000 W / m / K; 1100 W / m / K to 2500 W / m / K; 1100 W / m / K to 2000 W / m / K; 1100 W / m / K to 1800 W / m / K; 1100 W / m / K to 1600 W / m / K; 1100 W / m / K to 1400 W / m / K; 1100 W / m / K to 1200 W / m / K; > 1000 W / m / K; 1100 W / m / K; 1200 W / m / K; 1300 W / m / K; 1400 W / m / K; 1500 W / m / K; 1600 W / m / K; 1700 W / m / K; 1800 W / m / K; 1900 W / m / K; 2000 W / m / K; 2100 W / m / K; 2200 W / m / K; 2300W / m / K; 2400 W / m / K; 2600 W / m / K: 2600 W / m / K; 2700 W / m / K; 2800 W / m / K; 2900 W / m / K; or 3000 W / m / K; or any range or value therebetween. The thermal conductivity values mentioned in this paragraph can be the thermal conductivity values of the single crystal boron arsenide at room temperature, and can be measured using a method described in the examples.

[0038] in certain embodiments, the photoluminescence (PL) spectrum of the single crystal boron arsenide at a temperature 4 K can have a peak between 1.79 eV and 1.8 eV with full with half maxima (FWHM) 0.0005 eV to 0.001 eV. to certain embodiments, the photoluminescence (PL) spectrum of the single crystal boron arsenide at a temperature 4 K can have a peak between 1.67 eV and 1.69 eV with FWHM 0.03 to 0.1 eV: 0.03 to 0.08 eV; 0.03 to 0.07 eV; or 0.04 to 0.06 eV, and a peak between 173 eV and 175 eV with FWHM 0.03 to 0.1 eV; 0.03 to 0.08 eV; 0.03 to 0.07 eV; or 0.04 to 0.06 eV. In certain embodiments, the photoluminescence (PL) spectrum of the single crystal boron arsenide at a temperature 4 K can have a peak between 1.67 eV and 1.69 eV with FWHM 0.03 to 0.08 eV. and a peak between 1.73 eV and 175 eV with FWHM 0.03 to 0.08 eV. The photoluminescence (PL) spectrum of the single crystal boron arsenide at a temperature 4 K can be measured using a method described in the examples.

[0039] Impurity level in the single crystal boron arsenide can be less than 0.05 ppm. In certain embodiments, the impurity level in the single crystal boron arsenide is less than 0.01 ppm; In certain embodiments, the impurity level in the single crystal boron arsenide is < 0.05 ppm to 0.001 ppm; <0.05 ppm to 0.0001 ppm; <0.05 ppm to 0.00001 ppm; <0.05 ppm to 0.000001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; <0.01 ppm to 0.00001 ppm or <001 ppm to 0.000001 ppm.

[0040] Silicon impurity level in the single crystal boron arsenide can be less than 0.05 ppm. In certain embodiments, the silicon impurity level in the single crystal boron arsenide is less than 0.01 ppm. In certain embodiments, the silicon impurity level in the single crystal boron arsenide is < 0.05 ppm to 0.001 ppm; <0.05 ppm to 0.0001 ppm; <0.05 ppm to 0.00001 ppm; <0.05 ppm to 0.000001 ppm; < 0.01 ppm to 0.001 ppm; <0.01 ppm to 0.0001 ppm; <0.01 ppm to 0.00001 ppm or <0,01 ppm to 0.000001 ppm. Silicon impurity level in the single crystal boron arsenide can be the Silicon concentration in the single crystal boron arsenide.

[0041] Carbon impurity level in the single crystal boron arsenide can be less than 0.01 ppm. In certain embodiments, the carbon impurity level in the single crystal boron arsenide is < 0.01 ppm to 0.001 ppm: <0.01 ppm to 0.0001 ppm; <0.01 ppm to 0.00001 ppm; or <0.01 ppm to 0.000001 ppm. Carbon impurity level in the single crystal boron arsenide can be the carbon concentration in the single crystal boron arsenide.

[0042] Certain aspects are directed to a composition containing a single crystal boron arsenide. The single crystal boron arsenide can be a single crystal boron arsenide described herein. The single crystal boron arsenide can contain a single crystal of boron arsenide, in certain embodiments, the single crystal boron arsenide is prepared by the melt growth, such as a flux growth method. In certain embodiments, the single crystal boron arsenide is prepared by the Bridgman growth method, The single crystal boron arsenide formed can have a cubic crystal structure. In certain embodiments, the single crystal boron arsenide formed has a face centered zinc blende structure.

[0043] The single crystal boron arsenide and / or the composition containing the single crystal boron arsenide can be included in a electronics material including but not limited to electronics thermal management systems, solar cells, space electronics, circuits such as radiation-hardened circuits, optoelectionic materials, photonic and integrated photonic devices, power electronics and integrated devices, RF electionics and integrated devices, advanced sensors and integrated devices, high power laser system and integrated devices, monolithic electronic packages and circuits, advanced packaging and heterogeneous integration, Multi Chip integration, MEMS and integrated devices, semiconducting devices requites effective thermal solutions or litre.

[0044] Also disclosed are the following Aspects 1 to 50 of the present inventive concept.[0045) Aspect 1 concerns a method to produce a single crystal boron arsenide, the method comprising: contacting elemental boron with elemental arsenic to form a reaction mixture; maintaining or keeping the reaction mixture at a temperature above the melting point of arsenic for an effective amount of time to form a product mixture comprising the single crystal boron arsenide and liquid arsenic; cooling the product mixture for a predetermined amount of time; and separating the liquid arsenic from the tingle crystal boron arsenide.

[0046] Aspect 2 concerns the method of aspect 1, wherein the reaction mixture at a temperature 820CC to 900 °C to form the product mixture.

[0047] Aspect 3 concerns the method of aspect 1, wherein the reaction mixture at a temperature 840 °C to 900 °C to form the product mixture.

[0048] Aspect 4 concerns the method of any one of aspects 1 to 3, wherein the elemental boron and elemental arsenic are contacted at a boromarsenic molar ratio of 1:1 to 1:10.

[0049] Aspect 5 concerns the method of any one of aspects 1 to 3, wherein the elemental boron and elemental arsenic are contacted at a boromarsenic molar ratio of 1 :4 to 1 :10.

[0050] Aspect 6 concerns the method of any one of aspects 1 to 5, wherein the elemental boron and elemental arsenic are contacted at an oxygen level less than 1 ppm, and a moisture level less than 1 ppm.

[0051] Aspect 7 concerns the method of any one of aspects 1 to 6, wherein the elemental boron comprises crystalline boron.

[0052] Aspect 8 concerns the method of any one of aspects 1 to 7, wherein the elemental boron has a purity greater than 99%,

[0053] Aspect 9 concerns the method of any one of aspects 1 to 8, wherein the elemental arsenic has a purity greater than 99%.

[0054] Aspect 10 concerns the method of any one of aspects 1 to 9, wherein the reaction mixture has an impurity level less than 0.1 ppm.

[0055] Aspect 11 concerns the method of any one of aspects 1 to 10, wherein the elemental boron and elemental arsenic are contacted in a reaction vessel having an impurity level less than 0,01 ppm.

[0056] Aspect 12 concerns the method of aspect 11 , wherein the reaction vessel is a quartz vessel, and wherein the quartz vessel is washed with hydrofluoric acid, rinsed with isopropyl alcohol and dried prior to contacting the elemental boron, and elemental arsenic in the quartz vessel.

[0057] Aspect 13 concerns the method of any one of aspects 1 to 12, wherein the effective amount of time is 1 to 3 weeks.

[0058] Aspect 14 concerns the method of any one of aspects 1 to 13, wherein the product mixture is coded to 750 to 780 °C at a rate of 0.5 to 1.5 °C / hour.

[0059] Aspect 15 concerns the method of any one of aspects 1 to 14, wherein the liquid arsenic is separated from the Single crystal boron arsenide by establishing a temperature gradient in the product mixture by keeping a first end of the product mixture at a first temperature, and a second end of the product mixture at a second temperature, wherein the second end is an opposite end of the first end, and the second temperature is lower than the first temperature.

[0060] Aspect 16 concerns the method of aspect 15, wherein the first temperature is 700 to 800 °C, and the second temperature is 700 °C or below.

[0061] Aspect 17 concerns the method of any one of aspects 1 to 16, wherein the single crystal boron arsenide formed has a cubic crystal structure.

[0062] Aspect 18 concerns the method of any one of aspects 1 to 17, wherein the single crystal boron arsenide formed has a face centered zinc-blende structure.

[0063] Aspect 19 concerns a method to produce a single crystal boron arsenide, the method comprising: providing a reaction vessel with or without a boron arsenide crystal seeding crystal; providing elemental boron, and elemental arsenic tothe reaction vessel to form a reaction mixture in the reaction vessel; changing a temperature of the reaction mixture from a first temperature to a second temperature, from the second temperature to a third temperature, fromthe third temperature to the second temperature, and men from the second temperature to the first temperature, to form a product mixture comprising a single crystal boron arsenide and liquid arsenic, wherein the second temperature is higher man both the first temperature, and the third temperature; and separating the liquid arsenic from the single crystal boron arsenide.

[0064] Aspect 20 concerns the method of aspect 19, whereinthe first temperature is 820 to 860 °C, the second temperature is 860 to 900 °C, and the third temperature is 820 to 860 °C,

[0065] Aspect 21 concernsthe method of aspect 19 or 20, wherein the temperature of the reaction mixture is changed by moving the reaction vessel comprising the reaction mixture, from a first temperature zone to a second temperature zone, fromthe second temperature zone to a mind temperature zone, fromthe third temperature zone tothe second temperature zone, and then from the second temperature zone to the first temperature zone, wherein the first temperature zone has a temperature of 820 to 860 °C, the second temperature zone has a temperature of 860 to 900 °C, andthe third temperature zone has a temperature of 620 to 860 °C.

[0066] Aspect 22 concerns the method of aspect 19, wherein the first temperature is 830 to 860 °C, the second temperature is 860 to 900 °C, and the third temperature is 830 to 860 °C.

[0067] Aspect 23 concerns the method of aspect 19 or 22, wherein the temperature of the reaction mixture is changed by mowing the reaction vessel comprising the reaction mixture, from a first temperature zone to a second temperature zone, from the second temperature zone to a third temperature zone, fromthe third temperature zone tothe second temperature zone, and then from the second temperature zone to the first temperature zone, wherein the first temperature zone has a temperature of 820 to 860 °C, the second temperature zone has a temperature of 860 to 900 °C, andthe third temperature zone has a temperature of 820 to 860 °C.

[0068] Aspect 24 concerns the method of any one of aspects 19 to 23, wherein the first, second, and third temperature zones are formed in a furnace, and wherein the secondtemperature zone is formed over the first temperature zone, and the third temperature zone is formed over the second temperature zone.

[0069] Aspect 25 concerns the method of aspect 24, wherein the reaction vessel comprising the reaction mixture Is moved between the temperature zones at 0.02 to 0.1 mm / sec, and is rotated at 3 to 10 rotations per minute while moving between the temperature zones.

[0070] Aspect 26 concerns the method of any one of aspects 19 to 25, wherein the elemental boron and elemental arsenic is provided to the reaction vessel at a boron:arsenic molar ratio of 1:1 to 1 :10.

[0071] Aspect 27 concerns the method of any one of aspects 19 to 25, wherein the elemental boron and elemental arsenic is provided to the reaction vessel at a boron:arsenic molar ratio of 1 :4 to 1 : 10.

[0072] Aspect 28 concerns the method of any one of aspects 19 to 27, wherein the reaction vessel comprises a oxygen level less than 1 ppm and a moisture level less foari 1 ppm.

[0073] Aspect 29 concerns the method of any one of aspects 10 to 28, wherein the elemental boron comprises crystalline boron.

[0074] Aspect 30 concerns the method of any one of aspects 19 to 29, wherein the elemental boron has a purity greater than 99%.

[0075] Aspect 31 concerns the method of any one of aspects 19 to 30, wherein the elemental arsenic has a purity greater than 99%.[0076) Aspect 32 concerns the method of any one of aspects 19 to 31, wherein the reaction mixture has an impurity level less than 0.1 ppm.

[0077] Aspect 33 concerns the method of any one of aspects 19 to 32, wherein the reaction vessel has an impurity level less than 0.01 ppm.

[0078] Aspect 34 concerns the method of any one of aspects 19 to 33, wherein the reaction vessel is a quartz vessel, and wherein the quartz vessel is washed with hydrofluoric add, rinsed with isopropyl alcohol, and dried prior to providing the elemental boron and the elemental arsenic to the quartz vessel.

[0079] Aspect 35 concerns the method of any one gf aspects 19 to 34, wherein the step of changing the temperature of the reaction mixture from the first temperature to the second temperature, from the second temperature to the third temperature, from the third temperature to the second temperature, and then from the second temperature to the first temperature, is repeated.

[0080] Aspect 36 concerns the method of any one of aspects 19 to 35, wherein the liquid arsenic is separated from the single crystal boron arsenide by establishing a temperature gradient in the product mixture by keeping a first end of the product mixture at a fourth temperature, and a second end of the product mixture at a fifth temperature, wherein the second end is an opposite end of the first end, and the fifth temperature is lower than the fourth temperature.

[0081] Aspect 37 concerns the method of aspect 36, wherein the fourth temperature is 700 to 800 °C, and the fifth temperature is 700 °C or below.

[0082] Aspect 38 concerns the method of any one of aspects 19 to 37, wherein the single crystal boron arsenide formed has a cubic crystal structure.

[0083] Aspect 39 concerns the method of any one of aspects 19 to 37, wherein the single crystal boron arsenide formed has a face centered zinc-blende structure.

[0084] Aspect 40 concerns a single crystal boron arsenide having at least one dimension greeter than 2 mm.

[0085] Aspect 41 concerns the single crystal boron arsenide of aspect 40, wherein the single crystal boron arsenide has a cubic crystal structure.

[0086] Aspect 42 concerns the single crystal boron arsenide of aspect 40 or 41 , wherein the single crystal t»ron arsenide has a face centered zinc-blende structure.

[0087] Aspect 43 concerns the single crystal boron arsenide of any one of aspects 40 to 42, comprising a carrier concentration less than 1018 / cm3, preferably less than 1017 / cm3, at room temperature.

[0088] Aspect 44 concerns the single crystal boron arsenide of any one of aspects 40 to 43, having a thermal conductivity greater than 1000 Wm-1K-1, at room temperature.

[0089] Aspect 45 concerns the single crystal boron arsenide of any one of aspects 40 to 44, comprising an impurity level less than 0.05 ppm.

[0090] Aspect 46 concerns the single crystal boron arsenide of any one of aspects 40 to 45, comprising a silicon impurity less than 0.05 ppm.

[0091] Aspect 47 concerns the single crystal boron arsenide of any one of aspects 40 to 46, comprising a carbon impurity less than 0.01 ppm.

[0092] Aspect 48 concerns the single crystal boron arsenide of any one of aspects 40 to 47, comprising a carbon impurity less than 0.01 ppm.

[0083] Aspect 49 concerns the single crystal boron arsenide of any one of aspects 40 to 48, wherein the photoluminescence (PL) spectrum of the single crystal boron arsenide at 4 Khave a peak between 1.79 eV and 1.8 eV with full with half maxima (FWHM) 0. 0005 eV to 0.001 eV, a peak between 1.67 eV and 1.69 eV with FWHM 0.03 to 0.1 eV and / or a peak between 1.73 eV and 1.76 eV With FWHM 0.03 to 0.1 eV.

[0094] Aspect 50 concerns a composition comprising a single crystal boron arsenide of any one of claims 40 to 49, and / or prepared by a method of any one of claims 1 to 39.

[0095] The foregoing summary, as well as the following detailed description, will be better understood when read in conjunction with the appended drawings. For the purpose of illustration, there is shown in the drawings certain embodiments of the disclosed subject matter. It should be understood, however, that the disclosed subject matter is not limited to the precise embodiments and features shown. The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an implementation of systems and methods consistent with the disclosed subject matter and, together With the description, serves to explain ad vantages and principles consistent with the disclosed subject matter, in which:

[0098] FIGs. 1A-E show a set of schematic diagrams, graphs and photographs of Melt growth of cubic BAs using liquefied As as reaction media. FIG. 1 A shows a phase diagram of As[23). FIG. 1B shows a schematic diagram showing single crystals of BAs grown inside liquid As. FIG.1C shows an optical image of pristine single crystals on mm scales grown from liquid As reaction media. FIG. 1D shows a schematic of the zinc-blende crystal structure of cubic Bas and FIG.1B shows an X-ray diffraction pattern on large BAs single crystal.

[0097] FIGs. 2A-B show a pair of graphs showing the Raman spectrum of synthesized BAs. FIG. 2A shows a comparison of the Raman spectrum in log scale on BAs synthesized via CVT and melt growth method. FIG. 2B shows a Raman spectrum in log scale at different locations within a single crystal at room temperature, showing high homogeneity of the sample. Inset is the Images of the crystal used.

[0098] FIGs.3A-D show a set of graphs of Experimental Photoluminescence (PL) spectra of synthesized BAs. FIG. 3A shows PL spectra for CVT grown crystals at 4 K. FIG.3B shows PL spectra for melt-grown crystals at 4 K. FIG.3C is PL spectra of melt grown crystal from 4 K to 80 K. FIG, 3D shows PL spectra of melt grown crystal from 90 K to 300 K.[0099) FIGs. 4A-B show a pair of graphs showing the transport result of BAs from flux methods. FIG. 4A shows a graph of magnetic field dependence of Hall Resistivity ρxyfor four BAs single crystals. Inset temperature dependence of resistivity ρxxof BAs. FIG.4B is a graph of estimated carrier density in log scale from multiple BAs single crystals grown via meltmethod and the comparation of carrier density between our work (solid dots) and previous results (open dots) using CVT methods.

[0100] FIG. 5 shows a flow chart diagram of melt growth method for growing single crystal BAs according to one example of the present disclosure.

[0101] FIG. 6 shows a flow chart diagram of Bridgman growth method for growing single crystal BAs according to one example of the present disclosure.

[0102] FIG. 7 shows a schematic diagram of a Bridgman furnace according to one example of the present disclosure.

[0103] FIG. 8 shows photographs of characteristic resulting BAs crystals as grown by the Bridgman growth method.

[0104] FIGs. 9A-C show synthesis of c-BAs using Bridgman method according one example .. FIG. 9A shows a schematic drawing of the growth apparatus of a vertical three- zone Bridgman system. FIG. SB shows an optical image of c-BAs on mm scale grown from Bridgman method, FIG, SC shows X-ray diffraction of c-BAs single crystal.

[0105] FIG. 10A-B show Raman spectrum of c-BAs. FIG. 10A shows comparison of the Raman spectrum In log scale for c-BAs synthesized via Bridgman, CVT and Flux methods. FIG. 10B shows Raman spectrum in log scale at tour different zones within a single c-BAs crystal grown via Bridgman method (see inset).

[0108] FIG. 11A-C show photoluminescence spectra of c-BAs. FIG. 11A shows comparison of PL spectra of c-BAs synthesized via CVT, Flux and Bridgman method, FIG. 11B & C shows temperature dependent of PL spectra of c-BAs synthesized via Bridgman method. The symbol " indicates the emissions from unintended impurities possibly from alumina crucibles.

[0107] FIGs. 12A-B show transport results of c-BAs from Bridgman method. FIG. 12a shows Hall resistivity of four c-BAs single crystals at room temperature. Inset: temperature dependent resistivity of c-BAs, FIG. 12B shows estimated carrier density In log scale from multiple c-BAs single crystals grown via Bridgman method. The comparation of carrier density between this work (purple bails), the flux grown method (green dash line) and the previous work (gray open symbols) using CVT methods.DETAILED DESCRIPTION

[0108] It will be appreciated that for simplicity and clarity of illustration, where appropriate, reference numerals have been repeated among the different figures to indicate corresponding or analogous elements. In addition, numerous specific details are set forth in order to providea thorough understanding of the embodiments described herein. However, it will be understood by those of ordinary skill in the art that the embodiments described herein can be practiced without these specific details. In other instances, methods, procedures, and components have not been described in detail so as not to obscure the related relevant feature being described. Also, the description is not to be considered as limiting the scope of the embodiments described herein. The drawings are not necessarily to scale, and the proportions of certain parts may be exaggerated to better illustrate details and features of the present disclosure.I. TERMINOLOGY

[0109] The phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. For example, the use of a singular term, such as, “a” is not intended as limiting of the number of items. Also, the use of relational terms such as, but not limited to, “top," “bottom,” “left,” “right,” “upper,” “lower," “down," “up," and “side,” are used in the description for clarity in specific reference to the figures and are not intended to limit the scope of the presently disclosed technology or the appended claims. Further, it Should be understood that any one of the features of the presently disclosed technology may be used separately or in combination with other features. Other systems, methods, features, and advantages of the presently disclosed technology will be. or become, apparent to one with skill in the art upon examination of the figures and the detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the presently disclosed technology, and be protected by the accompanying claims.

[0110] Further, as the presently disclosed technology is susceptible to embodiments of many different forms, it is intended that the present disclosure be considered as an example of the principles of the presently disclosed technology and not intended to limit the presently disclosed technology to the specific embodiments shown and described. Any one of the features of the presently disclosed technology may be used separately or in combination with any other feature. References to the terms “embodiment,” “embodiments,’' and / or the like in the description mean that the feature and / or features being referred to are included in, at least, one aspect of the description. Separate references to the terms "embodiment" “em“odiments," and / or the like in the description do not necessarily refer to the same embodiment and are also not mutually exclusive unless so stated and / or except as will be readily apparent to those skilled in the art from the description. For example, a feature, structure, process, step, action, or the like described in one embodiment may also be included in other embodiments but is not necessarily included. Thus, the presently disclosed technology may include a variety of combinations and / or integrations of the embodiments describedherein. Additionally, all aspects of the present disclosure, as described herein, are not essential for its practice. Likewise, other systems, methods, features, and advantages of the presently disclosed technology will be, or become, apparent to one with skill in the art upon examination of the figures and the description. It is intended that ail such additional systems, methods, features, and advantages be included within this description, be within the scope of the presently disclosed technology, and be encompassed by the claims.

[0111] Any term of degree such as, but not limited to, “substantially,” as used in the description and the appended claims, should be understood to include an exact, or a similar, but not exact configuration. For example, “a substantially planar surface” means having an exact planar surface or a similar, butnot exact planar surface. Similarly, the terms “about” or “approximately," as used in the description and the appended claims, should be understood to include the recited values or a value that is three times greater or one third of the recited values. For example, about 3 mm includes all values from 1 mm to 9 mm, and approximately 50 degrees includes all values from 16,6 degrees to 150 degrees.

[0112] the term "Coupled" is defined as connected, whether directly or indirectly through intervening components, and is not necessarily limited to physical connections. The connection can be such that the objects are permanently connected or releasably connected. The terms "comprising," "including" and "having" are used interchangeably in this disclosure. The terms "comprising," "including" and "having" mean to include, but not necessarily be limited to the tilings so described. The term “real-time” or “real time” means substantially instantaneously.

[0113] Lastly, the terms for” and ’‘and / or," as used herein, are to be interpreted as inclusive or meaning any one or any combination. Therefore, “A, B, or C” or “A, B, and / or C” mean any of the following: "A", "8", or "C"; “A and B"; “A and C”; “B and C”; “A, B and C.” An exception to this definition will occur only when a combination of elements, functions, steps, or acts are in some way inherently mutually exclusive.

[0114] The term “ppm" refer to parts per million by weight, based on the total weight, of material that includes the component.

[0115] Terms "Melt growth" and flux growth” are used interchangeably through out this disclosure and refer to the same method .II GENERAL ARCHITECTURE

[0116] Described herein are a novel melt growth synthesis technique, and a novel Bridgman growth technique. The growth technique can be used for fabrication of high-quality single crystals of BAs motivated by the phase diagram of arsenic (As). The methods involvescalable melt growth utilizing liquid As as reaction media. The high quality of as-grown BAs crystals has been thoroughly evidenced via a combination of techniques including X-ray diffraction (XRD), Raman spectroscopy, temperature dependent photoluminescence (PL) spectroscopy, and transport results. Moreover, th heomogeneous high thermal conductivity exceeding 1000 VWm-K is further verified on the large single crystal by the time-domain thermoreflectance (TDTR).

[0117] N. Gokcen has assessed the As equilibrium phase diagram in 1989

[0023] . From the pressure-temperature phase diagram, the As has a tripte point at 817 °C and 37 bars [23, 24).Above 37 bars, an almost linear horizontal solid-liquid equilibria can be observed at around 820 °C with pressure extended up to 60 bars (FIG. 1 A) . Given the peritectic decomposition nature of BAs above 920 °C, and the liquid state of As above 820 °C above 37 bars, liquid As can be used as reaction media for control growth of BAs in the closed container (i.e,, sealed quartz tubes) under pressure larger than 37 bars. An excess amount of As is added inside the quartz tube to create the needed pressure for liquifying As which also serves as reactive flux during the crystal growth. This melt-flux growto technique has advantages over the CVT technique. The melt growth technique does not require a transport agent like CVT, reducing the chances of unintentional doping from the transport agent. Single-crystal growth from a liquid is usually faster and produces more boundaries, vacancies, or dislocations.

[0118] FIG. 1B is a schematic diagram illustrating the crystal melt growth in liquified As reactive media. The grey background represents As and the crystals inside the liquid As are crystallized BAs, with a flat facet <rf about 1~ 2 mm as shown in FIG. 1C, which is about one order larger than the crystals grown from CVT methods [25). FIG. 1 D shows the schematic of the zinc-blende crystal structure of cubic BAs and FIG. 1 E shows the XRD patterns with the X-ray’s Incident on the flat growth face of BAs single crystals synthesized by the melt growth. Similar as results from CVT growth, the preferred orientation for melt growth is along the (111) direction [26, 27).

[0119] Raman spectroscopies were performed to confirm the formation and compare the quality of BAs crystals using CVT and the melt growth technique. The Ramen spectrum of the crystals grown from DVT and melt method both shows first-order peaks dose to 700 cm-1and 720 cm-1which are vibrational fingerprints of BAs

[0028] and is due to the11B and vibration, respectively. Second-order peak above 1200 cm-1due to two-phonon scattering [28, 29] is also observed in both methods. The Raman peaks corresponding to second order overtone or combination modes are labelled in FIG. 2A [25, 28].

[0120] The crystals also show a much lower Raman background than the CVT-grown crystals. Raman spectroscopy from CVT-grown BAs has been reported to produce a broad signal background and asymmetric P1 and P2 phonon peaks (i.e., Fano resonance line shape) in the first-order peaks. the integrated signal background from 1050 cm-1 to 1150 cm-1 without any nearby sample peak signal interference. is used as a measure of the signal background. The absence of Fano resonance peaks, and tow Raman background ARaman, is established as a signature of high thermal conductivities because defect-mediated electronic Raman scattering dominates the Raman background in crystals with high point defect concentration

[0017] . The measured Raman background signals are clearly very low compared to the CVT-grown crystals. In FIG. 2A, the integrated background of melt grown BAs single crystals show one order smaller than the ones using CVT growth method.

[0121] To verify the homogeneity of the grown crystals which is problematic for CVT-grown crystals

[0015] , various location Raman spectroscopy measurements witein a single crystal was carried out, as shown in FIG. 2B, 10 pointe are randomly selected and all of their Raman spectrum show consistently a low background ARamanwithout signature of Fano resonance, dearly demonstrated the uniformly high quality of crystals with low defect concentrations.

[0122] Photoluminescence characterization is another powerful tool for studying shallow and deep defects. In the CVT grown crystals, typically two dominate shallow level donor- acceptor pair (DAP) emission at 1.4 and 1,6 eV are commonly observed, as shown in FIG, 3A, suggesting the incorporation of C and Si impurities during the crystal growth in the CVT process [20, 30], ft is generally believed the Si impurity originated from the reaction with quartz container during the CVT process. The peak at ~ 1.7 eV was initially attribued to the characteristic bandgap [15 , 25, 26].

[0123] Notably, the PL from melt growth shows clearly distinct patterns from CVT -grown samples, rather than one broad peak at ~1.7 eV from CVT-grown crystals, the melt grown BAs crystals shows three sharp emissions lines at 4K, denoted at P1 at 1.79 eV. P2 at 1.74 eV and P3 at 1.70 eV respectively in the FIG. 38. The bandwidth of these peaks Is rather sharp, indicating the intrinsic nature of these emissions. Moreover, the intensity of C-DAP and Si- DAP is quite weak compared to the intrinsic emissions of P1 , P2, P3, further demonstrate a limited density of impurities like Si and C in melt grow BAs single crystals compared to the ones grown from CVT.

[0124] Usually in the lll-V semiconductors such as n~type GaAs

[0031] , the lower the impurities carriers, the sharper the characteristics emission. According to this correlation, the sharp P1 and P2 in the BAs grown form melt method demonstrate a very low Impurity concentration, providing another evidence of superior quality to the crystals. The inset of FIG.3A shows the highest energy emission P3 in a high er resolution at 4 K. The peak split into two sub peaks, P3a at 1.7953 eV and P3b at 1.7962 eV clearly, which may be associated with the tine band structure or the quantum emitter of BAs. The assignment of P3 emission line still needs further investigated with detailed excitation power and theoretical supports.

[0125] Temperature dependent PL spectra of BAs ranging from 300 K to 4 K is summarized in FlGs, 3C and 3D. At room temperature, the spectra exhibit two prominent peaks situated around 1 ,4 eV and 1.73 eV. When temperature drops below 250 K, Si-DAP peak emerges at 1.6 eV, aligning with other research work. At temperatures below 130 K, P1 peak at 1.68eV emerges and becomes more and mote predominated when temperature is down to 4 K. When the temperature is lower than 100 K, the highest emission line P3 appears at 1.79 eV with the intensity increase mildly when temperature decreases.[0126) Temperature-dependent resistivity and carrier concentration, n, measurements were done further to investigate the qeuality of the BAs single crystals. Different samples from the same growth batch and multiple samples from different batches using the same melt growth method were measured, which exhibits consistentl rical transport behaviors. In the inset of FIG.4A, temperature-dependent resistivity is shown. The resistivity values readies 0.1 Ω-cm, which is an order of magnitude higher than previously reported values [17. 26] and indicates much lower impurity canter levels in the samples grown using the flux technique. Upon cooling, resistivity increases rapidly, indicating a semiconducting behavior. To estimate the carrier densityofthehigh-quality BAs, Hall resistivity measurements on multiple BAs single crystals are carried out, as shown in FIG: 4A. The positive Hall coefficient for all the samples indicates p-type carriers in all samples. Carrier concentrations are calculated from the Hall coefficientwhere Bzis the magnetic field, ρxyis the product of Hall resistance and sample thickness, e is the elementary charge. Room temperature carrier concentrations in the flux-grown samples are within the order of 1017-1018 / cm3, which is distinctly lower than the previously reported values from CVT -grown [17, 19. 25) as shown in FIG. 4B, further suggesting the growth method described herein has overwhelming advantage for better control of impurity doping and carrier concentration comparing to the CVT growth method. The preliminary teste on the TDTR measurements have shown uniform high thermal conductivities >1000 W / rn / K for the BAs crystals grown from these techniques.

[0127] Two new techniques were developed. In the first technique, As is used as melt flux to grow BAS single crystals with decent size and high quality. In a second technique, a Bridgman growth method used small BAs crystals as seeds and liquified As as reaction media. The high quality has been thoroughly evidenced via a combination of techniques including XRD, Raman spectroscopy, PL, transport, and TDTR measurements. Large-size BAs singleCrystals with higher quality can be grown with the technique. Th BAs single-crystal grown can be used for future widespread electronic applications.Material Synthesis: Melt-growth process

[0128] Referring to FIG. 5,. a method to produce a single crystal boron arsenide using a melt growth technique according to one example of the present disclosure is described. According to FIG. 5, single crystal BAs is synthesized by a melt growth technique 100 using liquified As as reaction media. Pure elements of crystalline B (99,9999%, Alfa Aesar) and As chunks (99.8899%, Alfa Aesar) are mixed with different molar ratios of BrAs in the Ar glovebox with oxygen and moisture level less than 0.1 ppm. To minimize the hazard at explosion caused by the As vapor pressure, the source materials are placed in specially designed quartz tube. Beginning at step 110, prior to the reaction, the quartz tube is immersed in dilute HF acid (< 2%) overnight to remove impurities during quartz tube production process, and then rinsed several times with distilled water and isopropyl alcohol before dried in an oven. Cleaning and drying of quartz tube before the crystal growth is crucial for high quality of single crystal (step 110). Alter materials are loaded, the quartz tube is evacuated with turbo pump with a pressure < 10-5Pa (step 130) and flame sealed (step 140). At step 150, the sealed quartz tube is placed vertically in the center of a well-calibrated box furnace with a uniform temperature distribution. The temperature gradient of the furnace is < 5-10 °C from the center of furnace to the edge of the front door.

[0129] Various trials with different motor ratios of B and As, growth temperature, time, and cooling rate, have been carried out, it was found that B : Asgrowth temperature at 870 °C, reaction time at this temperature for 1 week (step 160), and cooled at a cooling rate of 1°C / h to 780 °C (step 170), yield the largest single crystals. However, crystals may be grown with 8 ; As in the range 1:4 to 1 :10. At step 160, the furnace temperature may be in the range 840 - 900 °C. At step 170, the cooling rate may be in the range 0.5 to 1.5 °C / h.

[0130] At step 180, the excess As in the reaction media is then separated from the grown BAs single crystals by establishing a temperature gradient with hot end site at about 800 °C (in the range 700-800 °C ) and cold end at about 700 °C (in the range 600 - 700 °C).Material Synthesis: CVT process

[0131] Single crystal from CVT method was synthesized by using Iodine (I2) transport agents

[0025] . Pure elements of crystalline B (99.9999%, Alfa Aser) and As chunks (99.9999%, Alfa Aesar) are mixed with a motor ratio of 1:2 with small amount of Iodine (1.2 mg per cm3) Inside the quartz tube, A horintal two zone furnace is used for the growth. The mixture of source materials is placed at a high temperature zone of 900 °C and crystals are grown at the cold end temperature is set at 780 °C for 3 weeks.Material synthesis: Bridgman technique

[0132] Referring to FIG. 6, a method to produce a single crystal boron arsenide using a Bridgman growth technique according to one example of the present disclosure is described. Referring to FIG. 6, single crystal BAs is synthesized through a Bridgman growth technique 200 using small BAs crystals as seeds and liquified Arsenic as reaction madia; Pure elements of crystalline B (99.9999%, Alfa Asset) and As chunks (99.9999%, Alfa Aesar) are mixed with different molar ratios of B:As in the Ar glovebox with oxygen and moisture level less than 0.1 ppm. To minimize the hazard of explosion caused by the high As vapor pressure during heating up procedure, the source materials are placed in specially designed quartz tube. Beginning at step 210, prior to the readion, the quartz tube is immersed in dilute HF acid (< 2%) overnight to remove impurities during quartz tube production process, and then rinsed several times with distilled water and isopropyl alcohol before dried in an oven. Cleaning and drying of quartz tuba before the crystal growth is crucial for high quality of single crystal. The quartz tube is then disposed in an Ar glovebox having oxygen and moisture levels below 0,1 ppm (step 220). A carefully-selected small crystal of BAs is loaded at the tip of the quartz tube before loading other materials serving as the seed crystal for the Bridgman growth (steps 220 and 230). In step 220, the molar ratio of 8: As is preferably in the range 1:4 to 1;10. After materials are loaded, the quartz tube is evacuated with turbo pump with a pressure < 10-5Pa (step 240) and flame sealed (step 250),

[0133] At step 280, the seated quartz tube is placed vertically in a three zone Bridgman furnace (see FIG. 7) for the crystal growth process. Zone 1 and Zone 3 are set Up with a temperature range of 830 - 860 °C, while the Zone 2 is set up with a temperature range of 860 - 900 °C, respectively. All the three zones are heated to targeted temperature within 20 hours from room temperature. The quartz tube with the loaded samples is initially placed at the center of the Zone 3 (step 260) and slowly pulled up at a rate of 0.02 - 0.1 mm per minute with clockwise rotation at rotation rate of 2.0 - 10.0 rotations per minute (step 270). Once the samples reach to the top of Zone 1 , then, at step 280, the sample descends at a rate of 0.02 -0.1 mm per minute, with counterclockwise rotation at rotation rate of 3.0 - 10.0 rotations per minute until it reaches the bottom of the Zone 3 (step 290). The whole process 255 comprising steps 280, 270, 280 and 290, is repeated two times.

[0134] Various experiments were conducted with different molar ratios of B and As, ranging from 1:4 to 1 :10. All these ratios were effectively yielded single crystals. After the reaction is complete, at step 295. the excess As in the reaction medium is separated from the Grown BAs single crystals by establishing a temperature gradient, with the hot end at about 800 °C (in the range 700-800 °C) and toe cold end at about 700 °C (in the range 600-700 °C) . The grown crystals are then separated and selected for the measurements. FIG. 8 shows a resultinglump of crystalline BAs and a single crystal BAs resulting from Bridgman growth technique 200.Raman and PL Measurements

[0135] Raman and PL measurements were carried out using a laser wavelength of 488 nm, power of S mW and a diameter of 0.5 microns.X-ray Diffraction and Transport Measurements

[0136] The powder XRD within a range of 10° to 150º was performed at room temperature using a Rigaku Smartlab diffractometer with Cu Kα radiation on BAs single crystal with the largest facet aligned parallel with the sample holder.

[0137] Electrical transport behaviors of BAs was measured were performed using a Quantum Design Physical Property Measurement System (PPMS). For Hail voltage measurements, the contribution of the transverse resistance Rxxwhich was induced due to any possible misalignment of the two Hall probes, is further eliminated through as Rxxwill not change when the direction ofapplied magnetic field is changed to the opposite direction, Au / Gr films, each 50 nm thick, were deposited to avoid rectifying contacts.

[0138] White the present disclosure has been described with reference to various implementations, it will be understood that these implementations are illustrative and that the scope of the present disclosure is not Med to them. Many variations, modifications, additions, and improvements are possible. More generally, implementations in accordance with the present disclosure have been described in the context of particular implementations. Functionality may be separated or combined differently in various implementations of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.ReferencesThe following references are incorporated herein in their entireties:1 Slack, GA, Nonmetallic crystals with high thermal conductivity. Journal of Physics and Chemistry of Solids. 1973, 34(2): P- 321-335,2. Berman, R., F.E. Simon, and J.M. Ziman, The thermal conductivity of diamond at low temperatures. Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences, 1953. 220(1141): p. 171-183.3. Klemens, P. and D. Pedraza, Thermal conductivity of graphite in the basal plane. Carbon, 1994. 32(4): p. 735-741.4. Slack, G.A., Anisotropic thermal conductivity of pyrolytic graphite. Physical Review, 1962. 127(3): p. 694.5. Chen, K., et al, Ultrahigh thermal conductivity in isotope-enriched cubic boron nitride.Science. 2020, 367(6477): p. 555-559,6. Wei, R., et al.. Thermal conductivity of 4H-SiC single crystals. Journal of Applied Physics, 2013. 113(5).71 Li, S, et al., Themnal expansion confidents of high thermal conducting BAs and BP materials, Applied Physics Letters, 2019. 115(1 ).8. Chen, X., et al. ,Thermal expansion coefficient and lattice anharmonicity of cubic boron arsenide. Physical review applied, 2019. 11(6): p. 064070.9. Tian, F., etal., Mechanical properties of boron arsenide single crystal. Applied Physics Letters, 2019. 114(13): p. 131903.10. Mahat, S;, et al; Elastic constants of cubic boron phosphide and boron arsenide. Physical Review Materials, 2021; 5(3): p. 033606.11. U, S., et al, Thermal expansion coefficients of high thermal conducting BAs and BP materials. Applied Physics Letters, 2019. 115(1 ): p. 011901.12. Chu, T. and A, Hyslop, Crystal growth and properties of boron monoarsenide. Journal of Applied Physics, 1972. 43(2): p. 276-279.13. Kang, J.S.. et al, Integration of boron arsenide cooling substrates into gallium nitride devices. Nature Electronics, 2021, 4(6): p. 416-423.14. Liu T.-H. et al Simultaneously high electron and hole mobilities in cubic boron-V compounds: BP, BAs, and BSb. Physical Review B, 2018. 98(8): p. 081203,15. Shin. J., et al, High ambipolar mobility in cubic boron arsenide. Science, 2022. 377(6604): p. 437-440.16. Yue, S., et al., High ambipolar mobility in cubic boron arsenide revealed by transient reflectivity microscopy. Science, 2022. 377(6604): p. 433-436.17. Chen, X., et al., Effects of Impurities cm the Thermal and Electrical Transport Properties of Cubic Boron Arsenide. Chemistry of Materials, 2021. 33(17): p. 6974-6982.18. Xing, J., et al, Multimillimeter-sized cubic boron arsenide grown by chemical vapor transport via a tellurium tetraiodide transportagent. Applied Physics Letters, 2018. 112(26): p. 261901.19. Zhou, Y., et al, Peak thermal conductivity measurements of boron arsenide crystals. Physical ReviewMaterials, 2022. 6(6); p. L061601.20. Lyons, J.L, et al, Impurity-derived p-type conductivity in cubic boron arsenide. AppliedPhysics Letters, 2018. 113(25): p. 251902.21. Song, B», et al, Optical properties of cubic boron arsenide. Applied Physics Letters, 2020. 116(14): p. 141903.22. Liu, W., et al., A three-stage magnetic phase transition revealed in ultrahigh-quality van der Waals bulk magnet CrSBr. ACS nano. 2022. 18(10): p. 15917-15926.23. Gokcen, N..The As (arsenic) system. Bulletin of Alloy Phase Diagrams, 1989. 10(1 ): p. 11-22.24. Klement Jr, W., A. Jayaraman, and G. Kennedy, Phase diagrams of arsenic, antimony, and bismuth at pressures up to 70 kbars. Physical Review, 1963, 131(2); p. 632.25. U, S. et al, High thermal conductivity in cubic boron arsenide crystals. Science, 2018. 361(6402): p.579-581.26. Gamage, GA, et al, Effect of boron sources on the growth of boron arsenide Single crystals by chemical vapor transport. Applied Physics Letters, 2019. 115(9): p. 092103.27. Lv, B., et al., Experimental study of the proposed super-thermal-conductor: BAs. Applied Physics Letters. 2015. 106(7): p. 074105.28, Hadjiev, V., et al, Anomalous vibrational properties of cubic boron arsenide. Physical Review 8.2014. 89(2): p, 024308.29. Rai, A., et al, Effect of isotope disorder on the Raman spectra of cubic boron arsenide. Physical Review Materials, 2021. 5(1); p.013603.30. Meng, X., et al. Pressure - Dependent Behavior of Defect - Modulated Band Structure in Boran Arsenide, Advanced Materials, 2020. 32(45): p. 2001942.31. Bogardus, E.H. and H.B. Bebb, Bound-exciton, frae-exdton, band-acceptor. donor- acceptor, and auger recombination in GaAs. Physical Review, 1968. 176(3): p. 993.Example 1A flux growth technique for high quality cubic boron arsenide bulk single crystals

[6139] Thermal management stands as a paramount challenge in modem technology, especially in the realm of modem electronics. The evolution of technology over the past half- century, including the progressive miniaturization of transistors, intricate compactness, and novel fabrication methodologies, has resulted in the creation of high density power electronic and optoelectronic integrated circuits. These advancements have yielded circuits that are not only smaller, faster, and mere powerful, but also inevitably generate a significant amount of heat. For instance, data storage centers consume over 200 TWH of electricity annually and more than half of the total energy is used for coding

[0032] . The semiconductor industry also faces a significant technological challenge due to the presence of elevated hot-spot temperatures, which precipitates the degradation of device performance. In an effort to find potential solutions to the mounting thermal management challenges devices, much research has focused on diamond [33< 34] and graphitic materials [35-38j which achieve record high conductivity values up to about 3000 and 2000 W / m / K at 300K, respectively, due to their simple crystal structures and strong covalent bonding between the light elements

[0039] . Despite the exceptionally high conductivity [40, 41] the adoption of diamond remains constrained by the steep cost of high-quality and scalable materials synthesis caused by the intricate high pressures up to gigapascals and high temperatures involved in the process, and the large coefficient of thermal expansion (CTE) mismatch with common semiconductors. The thermal management applications of graphite are limited by the highly anisotropic heat transport

[0042] weak interlayer bonding, and the metallic behavior. Cubic boron nitride, another candidate material with high thermal conductivity of about 1600W / m / K at room temperature

[0043] requires an elaborate synthetic condition including pressures exceeding 10GPa and temperature surpassing 2000 °C. it also suffers limitations related to Size vield efficiency and cost considerations Recently unusual high thermal conductivity values, exceeding 1000 W / m / K at room temperature, have been predicted by first principles calculations and subsequently experimentally validated in semiconducting c-BAs, [44-47] which surpasses the conductivity benchmarks set by industrial standards. such as SIC and copper by more than three times

[0048] . The high thermal conductivity of c-BAs has been attributed to the combination of a large frequency gap between the acoustic and optical phonons and the bunching of the acoustic phonori dispersion curves caused by the unique mass ratio of the constituent atoms. Moreover, c-BAs has a better thermal expansion coefficient (CTE) match with silicon and other III— V semiconductors than diamond [49, 50] and comparable mechanical properties with other common semiconductors [51 , 52]. The thermalboundary conductance of GaN structures on c-BAs has been measured to be 250 MW / m / K, higher than that for diamond

[0053] . Furthermore, due to the high optical phonon energy, simultaneously high hole and electron mobilities (2110 and 1400 cm2V-1s , respectively) at room temperature

[0054] in c-BAs have been predicted from first principles calculations, which is revealed recently by high-resolution optical measurements at small low-defect regions in c- BAs crystals [55« 56].

[0140] The chemical vapor transport (CVT) method, reported by Lv et al. in 2015 [57, 58] based on further development of the work by Chu et al in 1972

[0059] is predominately used for the growth or o-Bas bulk single crystals. Despite the significant improvement in recent years [60, 61] it re mains a significantchaitenge to use the CVT method to obtain c-BAs crystals with tow and uniform defect concentrations and a size larger than several millimeters, The nature of spontaneous nucleation from the vapor phase supereaturation during the CVT process often yields small and clustered crystals from the unpredictable nucleation sites. Moreover, the difficulty in controlling unintentional impurity doping in CVT growth results in low bulk thermal conductivities and inconsistent electrical resistivity behavior in the grown crystals [62-68]. c- BAs crystals obtained by CVT often exhibit p-type conductivity with a hole concentration above 1018cm-3and up to 1021cm-3[45, 62, 64] that has been attributed to either unintentional carbon or silicon substitutional dopant impurities [62, 64, 66] In response to these challenges, introduced here is a different growth synthesis technique for high-quality single crystal growth of c-BAs. This method involves scalable flux growth utilizing liquid Arsenic (l-As) as a reaction medium. The high quality of these as grown c-BAs crystals has been thoroughly evidenced via a combination of techniques including x-ray diffraction (XRD), Raman spectroscopy, temperature-dependent photoluminescence (PL) spectroscopy, and electrical transport results.

[0141] N. Gokcen assessed the As equilibrium phase diagram in 1989

[0069] , From the pressure-temperature phase diagram, As has a triple at 817 °C and 37 bar [89, 70], Above 37 bar, an almost linear horizontal solid-flquid equilibrium can be observed at around 820 °C with pressure extended up to 60 bar shown in FIG. 1 A. Given the peritectic decomposition nature of c-BAs above 920 °C, and such a solid-liquid equilibrium line at 820 °C for an extended pressure range. l-As as a reaction medium was used for controlled growth of c-BAs in the closed container (i,e. , sealed quartz tubes) under pressures larger than 37 bar. Excess As is added inside the quartz tube to create the needed pressure tor liquifying As, which also serves as a reactive flux during crystal growth. This flux growth technique has advantages over the CVT technique. tn particular, the flux growth technique does not require a transport agent like CVT, reducing the chances of unintentional doping from the transport agent. Single-crystal growth from a liquid is usually fester and produces more uniform crystals with fewer defects.such as grain boundaries, vacancies, or dislocations. The detailed synthesis procedure is described in the supplementary material. FIG. 1B is a schematic diagram illustrating crystal growth in the l-As reactive medium. The gray background represents toe l-As, and the orange flakes represent c-BAs crystals inside the l-As. The crystals form wife a flat facet of around 2 mm as shown in FIG. 1C, which is about one order of magnitude larger than the crystals initially grown from CVT methods [45, 57, 58]. FIG. 1D shows the schematic of the zinc blende crystal structure of cubic c-BAs. FIG. 1E shows the XRD patterns wife the x-rays incident on the flat growth face of c-BAs single crystals synthesized by the flux growth method. Simitar to the respite from CVT growth, the preferred orientation for flux growth is along the (111) affection.

[0142] Raman spectroscopy was performed to confirm the formation

[0058] and compare the quality of c-BAs crystals grown using fee CVT and flux growth techniques. The Raman spectra of fee crystals grown from CVT and flux methods both show first-order peaks close to 700 and 720 cm-1, which are vibrational fingerprints of c-Bas

[0058] and are due to the11B- and10B- like longitudinal optical (LO) phonon modes, respectively. Second-order peaks above 1200 cm*1due to two-phonon scattering (58, 72] are also observed in both mefeods. The Raman peaks corresponding to second order overtones or combination modes are labeled in FIG. 2A [45, 58].[0143) The CVT grown crystals very often show asymmetric P1 and P2 phonon peaks (i. e., Fano resonance line shape) in the first-order peaks [FIG. 2A]. The integrated Raman signal background from 1050 to 1150 cm-1(ARaman), without any nearby sample peak signal interference, has also been used as a benchmark measure of c-BAs sample quality. The appearance of Fano resonance peaks and high Raman backgrounds ARaman often are signatures of low thermal conductivities because defect-mediated electronic Raman scattering dominates the Raman background in crystals with high point defect concentrations

[0045] , Most of fee CVT grown crystals have shown a wide spread of Raman signal backgrounds even at different locations within the same crystals, although occasionally one will be able to find small size crystals with relatively uniform sample quality

[0045] . Meat notably, the crystals from this flux growth technique overall show a much lower Raman background than the CVT-grown Crystals.

[0144] In FIG. 2A, fee integrated background ARamanof the flux grown c-BAs single crystal sample is one order of magnitude lower than the typical ones using the CVT growth method. To further verify the homogeneity of the flux grown crystals, which is problematic for CVT- grown crystals [55, 68], various location Raman spectroscopy measurements within a single crystal was carried out, as shown in FIG. 28. Ten pointe are randomly selected, and all the Raman spectra consistently show a low background ARamanwithout signature of Fanoresonances. This clearly demonstrates the uniformly high quality of crystals with low defect concentrations.[0145} Photoluminescence (PL) characterization is another powerful tool for studying shallow and deep defeats. AS shown in FIG, 3A, two different types of PL spectrum are commonly observed from the CVT-grown c-BAs crystals, in lower quality samples from GVT growth, two donor-acceptor pair (DAP) emission bands at 1.4 (labeled C-DAP) and -1 .6 eV (labeled Si-DAP) are commonly observed at 4K (labeled as CVT-1 in top curve of FIG. 3B). Based on the binding energies calculated from hybrid density functional theory (DFT), the PL band at -1 .4 eV has been assigned to recombination between CB donors and CAs acceptors while the PL band at -1 .6 eV has been assigned to recombination between SiB donors and SiAs acceptors [66, 73, 74]. The observation of these emission bands is associated with the incorporation of unintentional C and Si impurities during the CVT crystal growth process [64, 66, 74); It is generally believed the Si impurities originated from reaction with the quartz container during the CVT process. In addition, there is evidence from elemental analyses that both C and Si may be present as residual impurities in the B source material. In the higher quality samples from CVT growth, two additional PL bands, labeled P1 at 1.68 eV and P2 at 1.74 eV, are also observed [labeled as CVT-2 in bottom curve of FIG. 3A]. They were previously assigned to excitonic radiative recombination processes based on their superlinear excitation power dependence behaviors. P2 was assigned to near-bandgap free excitonic emission based on the revised DFT-derived low temperature bandgap of -1.8 eV and the estimated free exciton binding energy while P1 was tentatively escribed to excitons bound to neutral donors

[0066] . A four-component fit of this spectrum using Gaussian line shapes reveals the Si-DAP PL band as the strongest emission from this CVT-grown sample. The PL spectrum at 4K, from the flux-grown c-BAs sample, is shown in FIG. 3B. This sample also exhibits the same C-DAP, Si-DAP, and two excitonic PL emission bands (P1 and P2) as observed for the CVT-grown crystal. Most notably, a fit to this spectrum shows that the two DAP emission tends are much weaker compared to the intensities of the P1 and P2 excitonic PL bands. This strongly suggests that the concentration of residual carbon and silicon impurities in the flux- grown c-BAs sample is tower compared to those in the CVT-grown c-BAs crystal. This is consistent with Raman results and the room temperature hole concentrations found for these samples as discussed to FIGs. 4A"B. In addition, the fits reveal that the full-width at half maximum (FWHM) linewidths for excitonic PL bands P1 and P2 are about 30% smaller for the flux-grown sample compared to those for the CVT-grown c-BAs sample and suggests an overall improved crystallinity.

[6146] Finally, a previously unreported and very sharp PL band at ~1.795 eV (labeled P3) was also found from the flux-grown c-BAs sample, as shown in the inset of FIG. 3B. Underhigh resolution conditions, this emission is revealed to actually be a doublet with peak energies at 1.7953 (labeled P3a) and 17962 eV (labeled P3b), respectively, and with narrow FWHM linewidths of -0.4 eV. This very near bandgap emission also appears to be excitonic in nature based on its su perlinear intensity behavior observed from an excitation power study. The origin of the P3 emission line is unknown at tills time and will be the subject of further experimental and theoretical investigations

[0147] Temperature dependent PL spectra for the flux-grown c-Bas sample from 4 to 300K are summarized in FIGs. 3C and 3D. Several behaviors are evident First, the Si-DAP recombination is found to decrease faster relative to the C-DAP emission with increasing temperature as best shown in FIG. 3D such that at 300K only the C-DAP band is clearly observed. This is consistent with the much larger calculated binding energy for the CB donor (- 280 meV) compared to that for the SiB donor level (- 140meV) (74). Second, excitonic PL lines P1 and P3 decreased monotonically with increasing temperature with P1 not observed above -130K and P3 not found above -110K. Finally, PL band P2 (assigned to ffee excitonic near bandgap emission) shifts to slightly tower energies and broadens as the temperature is increased from 4 to 300K. It is the dominant PL band at 300K and exhibits a high energy tail between -190 and 300K. More detailed analyses of these spectra are beyond the scope of this paper and will be given in a future publication.

[0148] Temperature-dependent resistivity and room temperature carrier concentration, n, measurements were further done to investigate the quality of the flux growth c-BAs single crystals. Different samples from the same growth batch and multiple samples from different batches using the same flux growth method were measured and were found to exhibit consistent electrical transport behavior. In the inset of FIG. 4A, temperature-dependent resistivity ρxx, for sample 81 is shown. The resistivity value reaches dose 0.1 Ω cm near 300K, which is an order of magnitude higher than previously reported values [61 , 62] and indicates much lower impurity carrier concentrations in the samples grown using the flux technique. Upon cooling to 50K, the resistivity increases rapidly, indicating a semiconducting behavior. To estimate the carrier density of the high-quality c-BAs flux-grown samples. Hall resistivity measurements on multiple c-BAs single crystals were carried out. as shown in FIG. 4A. The positive Halt coefficient indicates p-type conductivity for all the samples. Carrier concentrations were calculated from the Hall coefficient n= Bz / ρxye, where Bz is the magnetic field, ρxyis the product of Hall resistance and sample thickness, and e is the elementary charge. Room temperature hole carrier concentrations in the flux-grown samples (solid squares in FIG. 48} are within the order of 1017-1018cm3, which is distinctly lower than the previously reported values for CVT-grown [45, 62, 64] c-BAs crystals [open symbols in RG..4B]. This further suggests that the flux-growth method has overwhelming advantages for better control ofimpurity doping and reduced carrier concentration compared to the CVT growth method. In conclusion, a different technique was developed using I-As as the flux to grow c-BAs single crystals with several millimeters size and high quality, which has been thoroughly revealed via a combination of techniques including XRD. Raman spectroscopy, PL, and transport measurements. This technique was extended to a relatively mere scalable Bridgman growth for c-BAs crystal growth. The flux-growth and Bridgman growth techniques, will have great potential to grow large wafer scale c-BAs single crystal substrates with much higher quality and will open fresh avenues for applications as electionic and thermal management materials in the future.Materials synthesis, Raman scattering, PL, x-ray diffraction, and transport measurements

[0049] Single crystal c-BAs is synthesized by a flux growth technique using liquid As as a reaction medium. Pure elements of crystalline B (99.9999%, Alfa Aesar.) and As chunks (99.9999%, Alfa Aesar) are mixed with different molar ratios of BAs in the Ar glovebox With oxygen and moisture levels less than 0.1 ppm. To minimize the hazard of explosion caused by the As vapor pressure, the source materials are placed in a specially designed quartz tube. Cleaning and drying of the quartz tube before the crystal growth is crucial for high quality of single cBAs crystals. After the materials are loaded, the quartz tube is evacuated using a turbo pump with a pressure < 10-5Pa and flame sealed. The sealed quartz tube is placed vertically in the center of a well-calibrated box furnace with a uniform temperature distribution. Various foals with different molar ratios of B and As, growth temperature, time, and cooling rate, have been carried out It was found that B: As 01:5, growth temperature at 870 reaction time at this temperature for 1 week, and a coding rate Of 1°C / h to 780 °C, yield the best single crystals. The excess As in the reaction media is then separated from the grown c-BAs single crystals by establishing a temperature gradient with hot end site at 800 °C and cold end at 700 °C. Single crystal c-BAs from CVT method is synthesized by using an Iodine (I2) transport agent

[0150] The X-ray diffraction was performed at room temperature using a Rigaku Smartlab diffractometer with Cu Kα radiation. The Raman experiments were done using a single-mode 488 nm solid state taser with 2 mW of power focused to a diameter of approx. 0.7 mm. The spectra were obtained in the backscattering geometry with incident and scattered light propagating normal to the sample surface. The photoluminescence (PL) spectra were obtained with the c-BAs crystals mounted in a Montana Instruments closed-cyde optical cryostat with the temperature varied from 4-300 K. The PL was excited with a 832 nm laser diode with 20 mW of power focused to a diameter of approx.20 mm. The emitted light was fiber-optic coupled to an Oxford / Andor spectrometer fitted with a thermoelectric-cooled Si charge-coupled device (CCD) detector.Electrical transport measurements were obtained using a Quantum Design Physical Property Measurement System (PPMS). 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Wang, “Pressure-dependent behavior of defect-modulated band structure in boron arsenide;* Adv. Mater, 32, 2001942 (2020),Example 2High-yield growth of high-quality cubic BAs single crystals using Bridgman method

[0152] The ongoing advancements in the semicondur industry have highlighted the importance of “more-than-Moore” and “beyond silicon" technologies for future semiconducting electronic devices. As large-scale monolithic integration and complexity increases, effective thermal management becomes crucial, especially for the high-power devices based on wide- bandgap (WBG) semiconductors like GaN [75, 76], and β-Ga2O3

[0077] -based electronic components

[0079] . Electronic devices must operate below 250º0, including transistors, diodes, and capacitors, to meet performance goals. However, WBG devices, such as a GaN monolithic converter operating at 10 MHz, can reach local heat densities as high as 6.4 kW / cm [76, 78] -comparable to the heat density of the surface of the Sun. A rough estimate shows that thermal dissipation issue is responsible for about 55% of the electronic failures. Thermal challenges are even more pronounced in the emerging electric vehicle industry, where automotive power conversion aims to achieve power density increases to 100 kW / K by minimizing component size and efficiently managing heat fluxes of up to 1000 W / cm2, underscoring the need for efficient thermal management from devices to packaging materials, and ultimately to heat sinks.

[0153] Effective thermal management solutions rely significantly on novel materials with high thermal conductivity. Diamond, with a conductivity of 2300 W / m-K at room temperature, remains the highest known, but its synthetic production is complex and costly. Graphite, with a conductivity of 2000 W / m-K, presents challenges due to its metallic nature and highlyanisotropic thermal properties, limiting its application in thermal management. Recently, cubic boron arsenide (c-BAs) has emerged as an attractive semiconductor due to its high thermal conductivity. In 2013, L. Lindsay etaL predicted ultrahigh thermal conductivities of several boron-related wide-gap semiconducting zinc-blende compounds through quantitative ab initio calculations [80). Notably, at room temperature, cubic boron arsenide (c-BAs) exceeds diamond in thermal conductivity according to their calculations. The exceptional thermal conductivity of c-BAs has been attributed to the combination of a large frequency gap between acoustic and optic phonons, and the bunching of the acoustic phonon dispersions. Later on, stuthes have shown phonon scattering including four phonons plays ah important role in this class of materials with a modified calculated thermal conductivity - 1300 W m-1K-1which nevertheless is still significantly higher than most of semiconducting materials such as Si7, GaN8, and SiC9. However, to experimentally verify the predicted thermal conductivity value is not an easy task. Firstly, it requires high-quality single crystals with minimum grain boundaries scattering. Unfortunately, boron-related materials are well known to be very difficult to make in dense bulk form such as single crystals and thin films. The high volatility and toxicity of As further complicates their syntheses. Secondly, the control of defect / carrier concentration is very important but meanwhile also very difficult to control during crystal and film growth. Defects and impurities can dramatically degrade the thermal properties. As pointed out by theoretical calculations, only 0.1% As vacancy concentration is enough to suppress the thermal conductivity of BAs from -2200 W m-1K-1down to 120 W m-1K-1based on three- phonon scattering process

[0084] . The theoretical calculation further suggests that As vacancy (as isolated point defects} need to be less than 0.004% to achieve thermal conductivity higher than 1000 W m-1K-1in the three-phonon scattering picture.

[0154] Despite these challenges, high thermal conductivities have been experimental demonstrated in both cubic BP (> SOO W m-1K-1) and BAs (> 1000 W m-1K-1) in specific selected crystals or regions [85-87]. This could provide revolutionary solutions for increasing heat dissipation issues for power devices with high thermal density. To further facilitate such application, high-quality, large size crystals will be imperative. So far, c-BAs synthesized via chemical vapor transport (CVT) method are facing significant challenges. These include difficulties in achieving low and uniform defect concentrations, unpredictable nucleation sites, and intentional dopant impurities, etc.[88-90). These Issues lead to low bulk thermal conductivities and inconsistent transport results. For instance. CVT grown c-BAs often show metallic behavior with p-type carrier concentration as high as 1021cm-3, which is attributed to the doping of carbon and silicon [86, 89). Liquid arsenic can be used as a reaction medium, has obtaining high-quality c-BAs with high uniformity, low defect density of carbon and silicon, relatively low carrier concentrations

[0091] , However, same with CVT grown crystals, scalabilityremains a key concern for future industrial applications in terms of cost and production efficiency.(0155) In this example, successful synthesis of c-BAs single crystals using the Bridgman method is reported. Widely employed in semiconductor manufacturing, the Bridgman method, along with the Czochralski technique, is used to scalable produce high-quality single crystals of materials such as Si and GaAs. This approach demonstrates a higher yield rate compared to the CVT method and results in crystals with superior uniformity, lower defect density, and reduced carrier concentrations, asconfirmed by X-ray diffraction (XRD), Raman spectroscopy, temperature-dependent photoluminescence (PL) spectroscopy, and transport measurements.

[0156] Bridgman method was developed by P.W. Bridgman in the 1920s for the solidification of a crystalline materials from its molten state

[0092] Generally, it has advantages such as generating high purity crystals, growing relatively large size, high degree of homogeneity, reduced grain boundaries, etc. Given a molten nature of As above 320 ºC and the advantages of Bridgman techniques, another approach to synthesize c-BAs using Bridgman method was designed. The schematic drawing of the three-zone Bridgman apparatus is depicted in FIG. 9A. The detailed synthesis profile is described in the supplementary section. As a result a substantial c-BAs lump is obtained, composed of a large number of single crystals with an average size of ~ 3 × 1 mm2, as illustrated in FIG. 9B, The size is comparable to the flux-grown samples

[0091] and roughly an order of magnitude larger than the crystals initially grown from CVT method [86, 93, 94] . FIG. 9C shows the X-ray diffraction (XRD) patterns of c-BAs synthesized by Bridgman method from 10 to 150°. Three sharp and sfrong peaks corresponding to the indices of (111 ), (222) and (333) are observed, confirming the high quality of c-BAs. Furthermore, the preferred orientation of the crystals is confirmed to along the (111 ) direction.

[0157] To confirm the quality of c-BAs, Raman spectroscopy was performed on the crystals synthesized via Bridgeman, CVT and flux method, which all exhibit first-order peaks in proximity to 700 cm-1and 720 cm-1. Their peaks serve as vibrational signatures of o-Bas

[0093] , and can be attributed to the11B- and10B-like longitudinal optical (LO) phonon modes. Moreover, all methods yield second order peaks above 1200 cm-1, which originate from two- phonon scattering [93, 95] and labeled as 2TO(X), 2TO(L) and 2LO(Γ) in FIG. 10A.

[0158] The presence of Fane resonance peaks and elevated Raman background in the Raman spectrum, as outlined in earlier research

[0086] , often indicates low thermal conductivities and tow sample qualities due to defect-dominated electronic Raman scattering predominates in crystals with high concentration of point defects. Typically, CVT-grown crystals demonstrate a higher Ranten signal background, whereas crystals grown from fluxmethod have shown much lower Raman background which is also consistent with measured uniform high thermal conductivities. The Raman background from the Bridgman grown crystals, in comparison with both CVT-grown and flux grown crystals shown in FIGs. 10A-B, also shows much lower background than CVT-samples while slightly higher than flux-grown samples, suggesting a relatively good quality of the sample, ft should be noted that weak Faroe resonance fine shape is observed in samples grown via Bridgman methods, suggesting that while the Bridgman method can produce scalable crystals, the crystal quality might be slightly compromised compared to those grown by the flux method.

[0159] To further verify the homogeneity of the Bridgman-grown crystals, Raman spectroscopy measurements were performed at various locations within a single crystal, as shown in FIG. 10B, Four regions are randomly selected, and all the Raman spectra consistently show a low background, showing a high homogeneous of the Bridgman-grown c- BAs crystals.[0160) FIGs. 11A-B show photoluminescence spectra of c-BAs. FIG, 11A shows comparison of PL spectra of c-BAs synthesized via CVT, Flux and Bridgman method, FIG, 11 B shows temperature dependent of PL spectra of c-BAs synthesized via Bridgman method. The symbol " indicates the emissions from unintended impurities possibly from alumina crucibles.

[0161] Photoluminescence (PL) characterization is another powerful tool for studying shallow and deep defects. In the CVT grown c-BAs single crystals, generally two PL bands, labeled P1 at 1.68 eV and P2 at 1.74 eV with broad bandwidth are observed, as shown in FIG, 11 A, Initially P1 was ascribed to excitons bound to neutral donors while P2 was assigned to near-bandgap free excitonic emission based on the revised DFT-derived low temperature band gap of 1.8 eV and the estimated free exciton binding energy [90). However, the emergence of this new and very sharp PL band at - 1.795 eV (labeled P3) from both Bridgman and flux grown c-BAs sample suggested that this assignment needs to be revisited. Additionally, two donor-acceptor pair (DAP) emission bands at -1.4 (C-DAP) and -1.6 eV (Si- DAP) are comrnonly observed at 4 K, which have been assigned to recombination between C8donors and CAs acceptors and recombination between SiBdonors and SiAs acceptors, respectively [90, 96), The observation of these emission bands is associated with the incorporation of unintentional C and Si impurities during the CVT crystal growth process. These C-DAP and Si-DAP peaks have been observed from the samples grown via flux and CVT methods. They are slightly higher in intensity in the Bridgman grown single crystals than flux-grown samples, but much smaller than most of the CVT-grown samples.

[0162] Bridgman and Flux grown single crystals exhibit the same three excitonic PL emission bands (P1 P2, and P3 labeled in the FIGS. 11A-C) and two DAP emission. Notably, the spectrum shows mat the two DAP emission bands are much weaker compared to the intensities of the P1 and P2 excitonic PL bands. This strongly suggests that the concentration of residual carbon and silicon impurities in the flux-grow and Bridgman method c-BAs sample Is tower compared to those in the CVT-grown c-BAs crystal This to consistent with Raman results and the rami temperature hole concentrations found for these samples as discussed in FIGs, 12A-B below. In addition, the fits reveal that the full-width at half-maximum (FWHM) linewidths for excitonic PL bands P1 and P2 are about much smaller for the Bridgman and flux-grown sample compered to those for the CVT-grown c-BAs sample and suggests an overall improved crystallinity. Similar as flux-grown samples, a very sharp PL band at * 1.795 eV (labeled P3) was also found from the Bridgman grown c-BAs sample, which has never been observed in the CVT-grown crystals before. This peak appears to be excitonic nature with rather short life time which will be discussed separately. In the test, there appears to be two extra DAP emission bands (at 1.498. 1.526) in addition to the Si-DAP and C-DAP from the crystals grown via Bridgman method, as marked in star symbol. These extra peaks might originate from the tiny amount of and unintentional impurities in the reaction, such as additional Aluminum or Zirconium transition metais from the Alumina and Zirconia crucibles used during the synthesis, which will be further Investigated in the future.

[0163] Temperature dependent PL spectra for the Bridgman -grown c-BAs sample from 4 to 300 K are summarized in FIGs. 11B and 11C. Several behaviors are evident. First, the Si- DAP recombination is found to decrease faster relative to the C-DAP emission with increasing temperature (as best shown In FIG. 11 C such that at 300 K only the C-DAP band to dearly observed).

[0164] This is consistent with the much larger calculated binding energy for the CB donor (-280 meV) compared to that for the Sis donor level (-140 meV)

[0096] , The extra emissions marked as the symbol of stars also survive up to 160 K. Second, excitonic PL lines P1 and P3 decreased monotonically with increasing temperature with P1 not observed above -80 K and P3 not found above -50 K. Finally. P2 band, which is assigned to free excitonic near bandgap emission, shifts to slightly lower energies and broadens as the temperature is increased from 4 to 300 K. It is the dominant PL band at 300 K and exhibits a high energy tail between *190 and 300 K.

[0165] To further investigate the quality of the Bridgman growth c-BAs single crystals, temperature-dependent resistivity and room temperature Hall measurements were conducted, as shown in FIGs. 12A-B. All samples were found to exhibit consistent semiconducting behaviors. In the insert of FIG. 12A, temperature dependence of resistivity pxxis shown. Theresistivity value reaches close to 0.43 Q-cm near 300 K, which is an order of magnitude higher than previously reported values and indicates lower impurity carrier concentrations in the samples grown using the Bridgman technique.

[0166] To estimate the carrier density of the high-quality c-BAs flux-grown samples, Hall resistivity measurements on multiple c-BAs single crystals were carried out at room temperature, as shown in FIG. 12B.

[0167] The positive Hall coefficient across all samples demonstrates p-type conductivity. At room temperature, tire carrier concentrations were determined from tire Hall coefficient n =where is the magnetic field, is the product of Hall resistance and sample thickness, and e is the elementary charge. The room temperature hole carrier concentrations in the Bridgman-grown samples are within the order of 1017-1018 / cm3, which is close to the previously reported best value for CVT-grown c-BAs crystals

[0089] . This observation strongly indicates that the Bridgman-growth method afters big advantages in terms of enhanced control over impurity and reduced carrier concentration compared to the CVT growth methods,

[0168] In summary, c-BAs single crystals was grown via Bridgman method, achieving high scalability with sizes of several millimeters and high quality. The crystal quality has been systematically characterized using a combination of techniques including XRD. Raman, PL, and transport measurements. The flux-growth and Bridgeman techniques will have immense potential to grow wafer-scale c-BAs single crystal substrates with significantly higher quality. These developments pave the way for exciting applications in electronic and thermal management materials to the future.Material Synthesis:

[0169] Single crystal BAs is synthesized through a Bridgman growth technique using small BAs crystals as seeds and liquified Arsenic as reaction media. Pure elements of crystalline B (99,9999%, Alfa Aesar.) and As chunks (99.9999%, Alfa Aesar) are mixed with different molar ratios of BAs in the Ar glovebox with oxygen and moisture level less than 0.1 ppm. To minimize the hazard of explosion caused by the high As vapor pressure during heating up procedure, the source materials are placed in specially designed quartz tube. Prior to the reaction, tire quartz tube is immersed in dilute HF acid (< 2%) overnight to remove impurities during quartz tube production process, and then rinsed several times with distilled water and isopropyl alcohol before dried in an oven. Cleaning and drying of quartz tube before the crystal growth is crudal for high quality of single crystal. A carefolly selected small crystal of BAs is loaded at the tip of the quartz tube before loading other materials serving as the seed crystal far tire Bridgman growth. After materials are leaded, the quartz tube is evacuated with turbo pump with a pressure < 10-5Pa and flame sealed. The sealed quartz tube is placed verticallyin a three zone Bridgman for the crystal growth process. Zone 1 and Zone 3 are sat up with a temperature range of 830 - 860 °C, while Zone 2 is set up with a temperature range of 860 - 900 °C, respectively. Ail the three Zone are heated to targeted temperature within 20 hours. The quartz tube with the loaded samples Is initially placed at the center of Zone 2 and slowly pulled up at a rate of 0.02 - 0.1 mm per minute, with clockwise rotation at rotation rate of 3.0 - 10.0 rotations per minute. Once the samples reach the top of Zone 1 , the sample is then descending at a rate of 0.05 - 0.2 mm per minute, with counterclockwise rotation at rotation rate of 3,0 - 10,0 rotations per minute until it reaches the bottom of Zone 3, The whole process will be repeated two times until the experiment is finished. Various experiments were conducted with different molar ratios of B and As, ranging from 1:4 to 1:10. All these ratios were effectively yielded single crystals. After the reaction is complete, the excess as in the reaction medium is separated from the grown BAs single crystals by establishing a temperature gradient , with the hot end at 800ºC and the cold end at 700 °C.

[0170] The X-ray diffraction was performed at room temperature using a Rigaku Smartlab diffractometer with Cu Kαradiation.

[0171] Electrical transport measurements were obtained using a Quantum Design Physical Property Measurement System (PPMS). Au over Cr films was deposited, each 50 nm thick, for ohmic electrical contacts.

[0172] The Raman experiments were done using a single-mode 488 nm solid state laser with 2 mW of power focused to a diameter of approx. 0.7 mm. The spectra were obtained in the backscattering geometry with incident and scattered light propagating normal to the sample surface. The photoluminescence (PL) spectra were obtained with the c-BAs crystals mounted in a Montana Instruments closed-cycle optical cryostat with the temperature varied from 4-300 K.

[0173] The PL was excited with a 532 nm laser diode with 20 mW of power focused to a diameter of approx. 20 mm. The emitted light was fiber-optic coupled to an Oxford / Andor spectrometer fitted with a thermoelectric-cooled Si charge-coupled device (CCD) detector.ReferencesThe following references are incorporated herein in their entireties:75, M. Meneghini, C.D. Santi, I, Abid, M. Buffolo, M. Cioni, R.A. Khadar L Nela, N. Zagni, A. Chini, F Medjdoub, G. Meneghesso, G. Verzellesi, E, Zanoni. and E. Matioli. “GaN-based power devices.: Physics, reliability, and perspectives, " J. Appl. Phys. 130(18), 181101 (2021).76. KJ. Chen, O. Haberlen, A. Udow, C. lin Tsai, T. Ueda, Y. Uemoto, and Y. Wu, “GaN-on- Si Power Technology: Devices and Applications" IEEE Trans. Electron Devices 64(3), 779- 795 (2017).77. S.J. Pearton, J. Yang, P.H. Cary, F. Ren, J. Kim, MJ. Tadjer, and MA Mastro, “A review of Ga2O3 materials, processing, and devices," Appt Phys. Rev. 5(1), 011301 (2018).78. H. Amano, Y. 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Reinecke, “First-Principles Determination of Ultrahigh Thermal Conductivity of Boron Arsenide: A Competitor for Diamond?," Phys. Rev. Lett. 111 (2), 025901 (2013).81. H.R. Shanks, P.O. Maycock, P.H. Sidles, and G.C. Danielson, "Thermal Conductivity of Silicon from 300 to 1400ºK," Phys. Rev. 130(5), 1743-1748 (1963).82. L. Lindsay, D.A. Broido, and T.L. Reinecke, “Thermal Conductivity and Large Isotope Effect in GaN from First Principles,” Phys. Rev. Lett. 109(9), 095901 (2012).83. R. Wei, S. Song, K. Yang, Y. Cui, Y. Peng, X, Chen, X. Hu, and X, Xu, "Thermal conductivity of 4H-SiC single crystals," J. Appl. Phys. 113(5), 053503 (2013).84. N.H. Protik, J. Carrete, NA Katoho. N, Mingo, and D. Broido,"Ab initio study of the effect of vacancies on the thermal conductivity of boron arsenide," Phys. Rev. B 94(4), 045207 (2016).85. J.S, Kang, M. Li, H. Wu, H. Nguyen, and Y. Hu, “Experimental observation of high thermal conductivity in boron arsenide" Science 361(6402), 575-578 (2018).86. S. U, Q. Zheng, Y. Lv, X. Uu, X, Wang, P.Y. Huang, D.G. Cahill,, and B. Lv,"High thermal conductivity In cubic boron arsenide crystals ," Science 361(6402), 579-581 (2018).87. F. Tian, B. Song, X. Chen, N.K. Ravichandran, Y. Lv, K. Chen, S. Sullivan, J. Kim, Y. Zhou, T.-H. Liu, M. Goni, Z. Ding, J. Sun. G.A.G.U. Gamage, H. Sun, H. Ziyaee, S. Huyan, L. Deng, J. Zhou, AJ. Schmidt, S, Chen. C.-W. Chu, P,Y. Huang, D. Broido, L Shi. G. Chen, and Z. Ren, “Unusual high thermal conductivity in boron arsenide bulk crystals," Science 361(6402). 582-685 (2018).88. J. Xing, X. Chen. Y. Zhou, James.C. Culbertson. JA Freitas, E R. Glaser, J. Zhou, L Shi. and N. Ni,"Multimillimeter-sized cubic boron arsenide grown by chemical vapor transport via a tellurium tetraiodide transport agent," Appl Phys. Lett. 112(26). 261901 (2018).89. Y. Zhou, C. Li. P. Koirala, GA Gamage. H. Wu, S. U, NK. Ravichandran, H. Lee, A. Dolocan, B. Lv, D. Broido, Z. Ren, and L. Shi, "‘Peak thermal conductivity measurements of boron arsenide crystals,” Phys. Rev. Mater. 6(6), LQ61601 (2022).90. M. Lyons. J.B. Varley. E.R. Glaser, J A Freitas, J.C. Culbertson. F. Tian, GA Gamage, H. Sun, H. Ziyaee, and Z. Ren, “impurity-derived p-type conductivity in cubic boron arsenide," Appl. Phys. Lett 113(25), 251902 (2018).91. P. Koirala, W. Liu. H. Wu, A.L.N. Kondusamy, N. Dhale, E.R. Glaser, S. White, J.C. Culbertson, JA Freitas, and B. Lv, “A flux growth technique for high quality cubic boron arsenide bulk single crystals," Appl. Phys. Lett; 123(20), 201901 (2023).92. P.W. Bridgman, °CERTAIN PHYSICAL PROPERTIES OF SINGLE CRYSTALS OF TUNGSTEN, ANTIMONY, BISMUTH, TELLURIUM, CADMIUM, ZINC, AND TIN," 1851-1932 (1924).93. V.G. Hadjiev, M.N, Iliev, B. Lv, Z,F. Ren, and C.W. Chu, “Anomalous vibrational properties of cubic boron arsenide.” Phys. Rev. B 89(2). 024308 (2014).94. B, Lv, Y, Lan, X. Wang, Q, Zhang, Y. Hu, A. J. Jacobson, D. Broido, G. Chen, Z. Ren, and C.-W. 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Claims

CLAIMSWhat is claimed is:

1. A method to produce a single crystal boron arsenide, the method comprising: contacting elemental boron with elemental arsenic to form a reaction mixture; maintaining the reaction mixture at a temperature above melting point of arsenic for an effective amount of time to form a product mixture comprising the single crystal boron arsenide and liquid arsenic; cooling the product mixture for a predetermined amount of time; and separating the liquid arsenic from the single crystal boron arsenide.

2. The method of claim 1 , wherein, the elemental boron and elemental arsenic are contacted at a boron:arsenic molar ratio of 1:1 to 1:10.

3. The method of claim 1 or 2, wherein, the elemental boron has a purity greater than 99%, and / or the elemental arsenic has a purity greater than 99%.

4. The method of any one of claims 1 to 3, wherein, the elemental boron and elemental arsenic are contacted in a reaction vessel having an impurity level less than 0.01 ppm.

5. The method of any one of claims 1 to 4, wherein, the product mixture is cooled to 750 to 780 °C at a rate of 0.5 to 1.5 °C / hour.

6. The method of any one of claims 1 to 5, wherein, the single crystal boron arsenide formed has a cubic crystal structure.

7. A method to produce a single crystal boron arsenide, the method comprising: providing a reaction vessel with or without a boron arsenide seeding crystal; providing elemental boron and elemental arsenic to the reaction vessel to form a reaction mixture in the reaction vessel; changing a temperature of the reaction mixture from a first temperature to a second temperature, from the second temperature to a third temperature, from the third temperature to the second temperature, and then from the second temperature to the first temperature to form a product mixture comprising a single crystal boron arsenide and liquid arsenic, wherein the second temperature is higher than both the first temperature, and the third temperature; and separating the liquid arsenic from the single crystal boron arsenide.

8. The method of claim 7, wherein, the first temperature is 820 to 860 °C, the second temperature is 860 to 900 °C, and the third temperature is 820 to 860 °C.

9. The method of claim 7 or 8, wherein, the elemental boron and elemental arsenic is provided to the reaction vessel at a boron:arsenic molar ratio of 1:1 to 1:10.

10. The method of any one of claims 7 to 9, wherein, the elemental boron has a purity greater than 99%, and / or the elemental arsenic has a purity greater than 99%.

11. The method of any one of claims 7 to 10, wherein, the reaction vessel has an impurity level less than 0.01 ppm.

12. The method of any one of claims 7 to 11 , wherein, the step of changing the temperature of the reaction mixture from the first temperature to the second temperature, from the second temperature to the third temperature, from the third temperature to the second temperature, and then from the second temperature to the first temperature is repeated.

13. The method of any one of claims 7 to 12, wherein, the single crystal boron arsenide formed has a cubic crystal structure.

14. A single crystal boron arsenide having at least one dimension greater than 2 mm.

15. The single crystal boron arsenide of claim 14, having a cubic crystal structure.

16. The single crystal boron arsenide of claim 14 or 15, further comprising: a carrier concentration less than 1018 / cm3, preferably less than 1017 / cm3, at room temperature.

17. The single crystal boron arsenide of any one of claims 14 to 16, having a thermal conductivity greater than 1000 W / m / K, at room temperature.

18. The single crystal boron arsenide of any one of claims 14 to 17, further comprising: an impurity level less than 0.05.

19. The single crystal boron arsenide of any one of claims 14 to 18, further comprising: a silicon impurity less than 0,05 and / or a carbon impurity less than 0.01.

20. The single crystal boron arsenide of any one of claims 14 to 19, wherein, the single crystal boron arsenide is prepared by a method of any one of claims 1 to 13.

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