A boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch and a preparation method thereof

Abstract

The application discloses a preparation method of a boron aluminum nitride / nitrogen terminal diamond two-dimensional electron gas heterojunction structure which improves lattice mismatch, and comprises the following steps: obtaining a 111 plane monocrystalline silicon substrate; epitaxially growing a monocrystalline boron nitride transition layer on the 111 plane monocrystalline silicon substrate; growing a diamond epitaxial layer on the surface of the monocrystalline boron nitride transition layer; performing nitrogen terminal treatment on the surface of the diamond epitaxial layer to form a nitrogen terminal surface; epitaxially growing monocrystalline boron aluminum nitride with an Al plane polar wurtzite structure and a donor impurity on the nitrogen terminal surface to form a boron aluminum nitride epitaxial layer, so as to form a boron aluminum nitride / nitrogen terminal diamond two-dimensional electron gas heterojunction. The preparation method breaks through the size limitation of a high-quality diamond substrate, effectively alleviates the lattice distortion of boron aluminum nitride on diamond in the epitaxial process, reduces the surface state and the dangling bond at the formed heterojunction interface, and improves the quality of the diamond heterojunction.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of semiconductor process, and particularly relates to a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch and a preparation method thereof. BACKGROUND

[0002] Diamond is a new generation of ultra-wide bandgap semiconductor material, which has the advantages of large bandgap, high carrier mobility, high thermal conductivity, etc., and has great advantages and potential in the application of new generation of high-voltage, high-power, high-temperature-resistant and radiation-resistant electronic devices. The p / n type electric conduction with simple preparation process and excellent performance is crucial to the application potential of diamond material. Like most semiconductor materials currently used, diamond must be doped in some form to introduce a high enough density of mobile carriers. However, the strong covalent bond and close-packed crystal structure of diamond are the source of its excellent material properties, but also make it very difficult to activate the bulk doping at room temperature. As the most promising acceptor impurity in diamond p-type doping, boron still has an activation energy as high as 0.37 eV, resulting in a carrier ionization rate of only a few per thousand of the boron doping concentration at room temperature. In addition, as the boron dopant concentration increases, the hole mobility of the doped diamond will decrease significantly, and heavy boron doping will also have a negative impact on the quality of the diamond crystal, thereby affecting the performance of the device. As for n-type doped diamond, the most commonly used donor impurity is phosphorus, and its activation energy is as high as 0.6 eV, and the carrier ionization rate at room temperature is even lower. When the doping concentration of phosphorus reaches 6.8 x 1018 cm-3, the activated electron concentration at room temperature is only 10 16 cm -3 . 11 cm -3 -3 cm-3. The difficulty of doping diamond semiconductors has seriously limited its development and application in the field of electronic devices.

[0003] In recent years, it has been widely observed experimentally that hydrogen-terminated diamond surfaces can exhibit p-type conductivity at room temperature. After treating diamond in a hydrogen plasma, a hydrogen-terminated diamond surface covered with C-H bonds is formed, and after being exposed to air, a two-dimensional hole gas (2DHG) accumulation layer about 10 nm below the diamond surface can be formed due to the transfer doping effect. The concentration of 2DHG is in the order of 10 12 -10 14 cm -2 , and the mobility is in the range of several tens to 200 cm 2 / Vs. Field effect transistors (FETs) based on hydrogen-terminated diamond p-type conduction have become the mainstream of diamond electronic device research, and have achieved a maximum output current density of 1.3 A / mm, a cutoff frequency of 70 GHz, a breakdown voltage of 2608 V, and an output power density of 4.2 W / mm at 2 GHz.

[0004] In view of the fact that it is very difficult to dope diamond n-type, while a series of significant progress has been made in p-type surface conduction, the realization of two-dimensional electron gas (2DEG) surface conduction based on diamond heterojunction can provide a new way for diamond n-type conduction. The two-dimensional electron gas at the diamond-based heterojunction interface can be provided by the donor impurity ionization of the barrier layer, or by the principle similar to that of nitride heterojunction, i.e. the polarization effect and surface state ionization of the barrier layer. This can break through the key difficulties of diamond n-type doping, such as low ionization rate and difficulty in forming high conduction at room temperature, and greatly improve the current density of diamond devices. First-principles studies have shown that a two-dimensional electron gas with a concentration of up to 5×10 12 cm -2 can be formed at the diamond / cubic boron nitride (c-BN) heterojunction interface by inducing channel charges through gate voltage, which can be used to prepare high-performance high electron mobility transistors (HEMTs).

[0005] However, in actual device preparation, diamond-based heterojunction based on two-dimensional electron gas n-type conduction needs to meet the following conditions. If diamond material with ultra-wide band gap (5.5eV) is used as the channel layer to accommodate two-dimensional electron gas, and another material is used as the barrier layer, the band gap width of the barrier layer should be greater than that of diamond. Only aluminum nitride (AlN) and boron nitride (BN) and other ultra-wide band gap semiconductor materials meet this requirement.

[0006] The two materials forming the heterojunction also need to form a band step suitable for the transport of two-dimensional electron gas, i.e. a potential well on the diamond side and a potential barrier on the barrier layer side. In the case of doping and ionization of the barrier layer to provide electrons to form a two-dimensional electron gas, the height of the potential barrier should be greater than the ionization energy of the donor impurities in the barrier layer, so that the donor impurities can be ionized.

[0007] In summary, there are the following technical difficulties in using diamond materials to realize two-dimensional electron gas heterojunction for n-type conduction. First, the lattice type and lattice constant of the material forming the heterojunction with diamond should be similar to that of diamond, meeting the process requirements of high-quality heteroepitaxy between the two materials. In addition, the band gap of the material should be greater than that of diamond, so that the channel layer suitable for the transport of two-dimensional electron gas can be formed at the diamond interface through the band step regulation means of the heterojunction interface. It is also required that the formed heterojunction can form a certain concentration of two-dimensional electron gas through polarization effect or doping and charge transfer effect.

[0008] However, from the perspective of preparation process, first, the appropriate material needs to be selected, and then the appropriate conditions for heteroepitaxy are adopted. However, the process difficulty brought by the difference in lattice constant for high-quality epitaxy has always been a key scientific problem that needs to be solved. In addition, appropriate means are needed to effectively regulate the band step of the newly formed heterojunction interface, and methods are needed to realize the two-dimensional electron gas concentration in the formed channel layer. SUMMARY

[0009] To address the aforementioned problems in the prior art, this invention provides a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch and its preparation method. The technical problem to be solved by this invention is achieved through the following technical solution:

[0010] A first aspect of the present invention provides a method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch, comprising the following steps:

[0011] Obtain a 111-sided single-crystal silicon substrate;

[0012] A single-crystal boron nitride transition layer is epitaxially grown on the 111-plane single-crystal silicon substrate; the single-crystal boron nitride includes: 111 cubic boron nitride, hexagonal boron nitride, or boron-faceted wurtzite boron nitride.

[0013] A diamond epitaxial layer is grown on the surface of the single-crystal boron nitride transition layer;

[0014] The surface of the diamond epitaxial layer is subjected to nitrogen termination treatment to form a nitrogen-terminated surface;

[0015] In one embodiment of the present invention, the nitrogen terminal treatment employs MBE process, RIE process, or ICP process.

[0016] A single-crystal boron-aluminum nitrogen (BOA) with a donor impurity-doped Al-plane polar fibrous wurtzite structure is epitaxially grown on the nitrogen-terminated surface to form a BOA / nitrogen-terminated diamond two-dimensional electron gas heterojunction. During the BOA growth process, the boron and aluminum composition in the BOA epitaxial layer is controlled by adjusting the ratio of boron source to aluminum source.

[0017] In one embodiment of the present invention, trimethylaluminum, trimethylboron and nitrogen are used as aluminum source, boron source and nitrogen source respectively during the formation of the boron-aluminum-nitrogen epitaxial layer.

[0018] During the growth of boron aluminum nitrogen, silicon sources, oxygen sources, or other suitable donor elements are added to achieve an n-type doped boron aluminum nitrogen epitaxial layer.

[0019] The second aspect of the present invention provides a boron aluminum nitride / diamond two-dimensional electron gas heterojunction structure for improving lattice mismatch, which is prepared by the preparation method provided in the first aspect of the present invention, comprising: a 111-plane single-crystal silicon substrate, a single-crystal boron nitride transition layer on the 111-plane single-crystal silicon substrate, a diamond epitaxial layer on the single-crystal boron nitride transition layer, a nitrogen-terminated surface on the diamond epitaxial layer, and a boron aluminum nitride epitaxial layer with an Al-plane polar fibrous wurtzite structure doped with donor impurities on the nitrogen-terminated surface;

[0020] The materials of the monocrystalline boron nitride transition layer include: 111 cubic boron nitride, hexagonal boron nitride, or boron-polarized fibrous wurtzite boron nitride.

[0021] The beneficial effects of this invention are:

[0022] 1. Diamond heterojunction devices are fabricated based on single-crystal silicon substrates. The diamond layer required for the heterojunction is obtained by epitaxial growth, which breaks through the size limitation of high-quality diamond substrates and reduces the manufacturing cost of heterojunctions, providing an effective method for obtaining large-size diamond heterojunctions.

[0023] 2. A three-layer epitaxial structure of single-crystal boron nitride, diamond, and boron aluminum nitride is adopted. First, the lattice constant of single-crystal boron nitride is similar to that of diamond to ensure the quality of the diamond epitaxial layer. At the same time, the lattice constant of the diamond epitaxial layer on boron nitride changes, further reducing the difference between the lattice constants of boron aluminum nitride and boron aluminum nitride. Combined with nitrogen termination treatment on the diamond surface, the lattice mismatch between diamond, boron aluminum nitride, and boron aluminum nitride is effectively alleviated, and the quality of boron aluminum nitride / nitrogen-terminated diamond heterojunction is improved.

[0024] 3. Through the polarization effect between the diamond layer and the boron-aluminum-nitrogen layer with Al-faced polar fibrous wurtzite structure, 2DEG can be formed at the diamond interface of the heterojunction; 2DEG can also be formed at the diamond interface of the heterojunction by utilizing the transfer doping effect between the boron-aluminum-nitrogen epitaxial layer with donor impurity doping and diamond; by combining the composition control of boron-aluminum-nitrogen and the terminal treatment process of diamond surface, the band hierarchy of the heterojunction interface can be controlled to form an electron potential well that is conducive to 2DEG transport.

[0025] 4. By using interface control methods to perform nitrogen termination treatment on the surface of the diamond layer, the surface states of the diamond can be reduced, which is conducive to the atomic bonding between diamond and boron aluminum nitrogen materials, and improves the nucleation quality of the boron aluminum nitrogen epitaxial layer on the diamond surface, so as to form a high-quality diamond novel wide bandgap heterostructure.

[0026] 5. Nitrogen terminal treatment alters the electron affinity of the diamond surface, thereby modulating the band structure of the diamond surface and generating an electron potential well in the band structure of the heterojunction formed with boron, aluminum, and nitrogen.

[0027] 6. By adjusting the ternary compound components boron, aluminum, and nitrogen, the lattice constant of boron, aluminum, and nitrogen can be controlled, reducing the lattice mismatch rate between boron, aluminum, and nitrogen and diamond. This effectively alleviates the lattice distortion of boron, aluminum, and nitrogen during the epitaxial process, reduces the surface states and dangling bonds at the heterojunction interface, and improves the heterojunction interface quality.

[0028] 7. A heterostructure is achieved by using the ternary compound boron-aluminum-nitrogen with variable composition. The band structure of the material is controlled by changing the composition of the ternary compound. The diamond surface of the diamond boron-aluminum-nitrogen interface is also treated with nitrogen terminal treatment, which changes the electron affinity of the diamond surface. This can effectively control the band structure of the heterojunction interface and generate an electron potential well suitable for 2DEG transport.

[0029] 8. Boron-aluminum-nitrogen (BNA) alloys are expected to possess properties such as high breakdown field strength and high thermal conductivity. Combining BNA with diamond, which has even better properties, to form novel semiconductor heterojunction materials and devices will broaden the application fields and development prospects of semiconductor heterojunction devices.

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0031] Figure 1 This is a schematic flowchart of a method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure to improve lattice mismatch, provided in an embodiment of the present invention.

[0032] Figure 2 This is a schematic diagram of a boron aluminum nitride / diamond two-dimensional electron gas heterojunction structure for improving lattice mismatch provided in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram illustrating the fabrication process of a boron aluminum nitride / diamond two-dimensional electron gas heterojunction structure for improving lattice mismatch, provided by an embodiment of the present invention.

[0034] Explanation of reference numerals in the attached figures:

[0035] 1-111-plane monocrystalline silicon substrate, 2-monocrystalline boron nitride transition layer, 3-diamond epitaxial layer, 4-nitrogen-terminated surface, 5-boron aluminum nitride epitaxial layer. Detailed Implementation

[0036] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0037] Example 1

[0038] like Figure 1 and Figure 3 As shown, a method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch includes the following steps:

[0039] Step 101: Obtain a 111-sided single-crystal silicon substrate 1.

[0040] Step 102: Epitaxially grow single-crystal boron nitride on the 111-plane single-crystal silicon substrate 1 to form a single-crystal boron nitride transition layer 2.

[0041] Among them, single-crystal boron nitride includes: 111 cubic boron nitride, hexagonal boron nitride, or boron-polarized fibrous zinc nitride.

[0042] Specifically, a single-crystal boron nitride film several micrometers thick was obtained by using plasma chemical vapor deposition (PCVD) with B2H6 and N2 as boron and nitrogen sources, respectively, under appropriate working pressure, substrate temperature and substrate negative bias.

[0043] Step 103: Epitaxially grow a diamond epitaxial layer 3 on the single-crystal boron nitride transition layer 2. Due to the heteroepitaxial growth, the lattice constant of the diamond epitaxial layer 3 changes, and the difference between it and the lattice constant of boron, aluminum, and nitrogen decreases.

[0044] Specifically, a diamond epitaxial layer 3 with a thickness of 20–100 nm was grown on the surface of a single-crystal boron nitride transition layer 2 using MPCVD process under the conditions of substrate temperature of 915 °C, microwave power of 3.9 kW, pressure of 320 mbar, hydrogen flow rate of 200 sccm, and CH4 concentration of 6%, at a growth rate of 3 μm / h.

[0045] Step 104: Perform nitrogen termination treatment on the surface of the diamond epitaxial layer 3 to form a nitrogen-terminated surface 4. The nitrogen termination treatment can be performed using processes such as MBE, RIE, or ICP.

[0046] Specifically, an MBE device was used, with the N-Plasma output power set to 150W, the substrate temperature to 450℃, and the N2 flow rate to 1 sccm. Under these conditions, the substrate was nitrided for 60 minutes to form a nitrogen-terminated surface 4.

[0047] Step 105: Epitaxially grow a single crystal boron aluminum nitrogen with a donor impurity-doped Al-faced polar fibrous wurtzite structure on the nitrogen-terminated surface 4 to form a boron aluminum nitrogen epitaxial layer 5, thereby forming a boron aluminum nitrogen / nitrogen-terminated diamond two-dimensional electron gas heterojunction.

[0048] Specifically, the composition of boron and aluminum in the boron-aluminum-nitrogen epitaxial layer 5 is controlled by adjusting the ratio of boron source to aluminum source during the boron-aluminum-nitrogen growth process.

[0049] Specifically, the MOVPE process was used at 1280℃ and 90mBar, with trimethylaluminum, trimethylboron, and nitrogen as the aluminum, boron, and nitrogen sources, respectively. The boron-aluminum-nitrogen epitaxial layer was generated by controlling the ratio of the boron source to the aluminum source during the boron-aluminum-nitrogen growth process.

[0050] Donor impurities are added during the growth of boron aluminum nitride (BON). Specifically, silicon sources, oxygen sources, or other suitable donor elements are added during the BON growth process to achieve an n-type doped BON epitaxial layer.

[0051] Specifically, such as Figure 2As shown, a heterojunction structure is prepared by the above steps 101-105, including: a 111-plane single crystal silicon substrate 1, a single crystal boron nitride transition layer 2 on the 111-plane single crystal silicon substrate 1, a diamond epitaxial layer 3 on the single crystal boron nitride transition layer 2, a nitrogen-terminated surface 4 on the diamond epitaxial layer 3, and a boron-aluminum-nitrogen epitaxial layer 5 with donor impurity doped Al-plane polar fibrous wurtzite structure on the nitrogen-terminated surface 4.

[0052] This embodiment ensures the quality of the diamond epitaxial layer 3 by first growing a single-crystal boron nitride transition layer 2 on a 111-plane single-crystal silicon substrate 1. Simultaneously, it alters the lattice constant of the diamond epitaxial layer 3, reducing the difference between its lattice constant and that of boron, aluminum, and nitrogen (BON), further guaranteeing the quality of the subsequently grown BON epitaxial layer 5. Furthermore, by adjusting the boron to aluminum composition ratio in the BON epitaxial layer 5, the lattice mismatch between diamond and the BON epitaxial layer is further reduced. Adjusting the boron-aluminum-nitrogen composition ratio can also alter the band structure of the BON material. Combined with nitrogen-terminated treatment of the diamond surface, this changes the electron affinity of the diamond surface, enabling band hierarchy control at the diamond-BON heterojunction interface and forming an electron potential well suitable for 2DEG transport. 2DEG can be generated at the heterojunction diamond interface through the polarization effect between the diamond layer and the Al-plane polar boron aluminum nitrogen epitaxial layer 5; 2DEG can also be generated at the heterojunction diamond interface through the transfer doping effect between the diamond epitaxial layer 3 and the donor-doped boron aluminum nitrogen epitaxial layer 5.

[0053] The heterostructure achieved in this embodiment differs from the traditional AlGaAs / GaAs heterostructure in several ways, and therefore the requirements for materials and processing conditions are also different:

[0054] First, the requirements for heterojunction materials differ. Traditional AlGaAs / GaAs heterostructures are purely single-crystal semiconductor heterojunctions, requiring both AlGaAs and GaAs materials to be single-crystal semiconductors. However, for the diamond heterojunction achieved in this invention, the diamond can be either single-crystal or polycrystalline.

[0055] Secondly, the requirements for material surface properties differ. Traditional heterostructures such as AlGaAs / GaAs do not require terminal structures on the GaAs material surface. However, for diamond heterostructures that can generate two-dimensional electron gas n-type conductivity, surface terminals are required on the diamond surface to adjust the electron affinity of diamond and form a boron-aluminum-nitrogen / diamond interface band structure suitable for 2DEG transport.

[0056] Finally, the formation mechanisms of 2DEG differ. In traditional AlGaAs / GaAs heterostructures, doping the AlGaAs barrier layer causes the Fermi levels of the two materials to align. The doped AlGaAs barrier layer then has a higher Fermi level than the GaAs layer, leading to ionization of donor impurities, the emergence of charge carriers, and their entry into the channel layer, thus forming a 2DEG. However, in the diamond heterojunction involved in this invention, 2DEG is formed on the diamond surface through the polarization effect or charge transfer of the epitaxial layer material.

[0057] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0058] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0059] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0060] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0061] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0062] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterostructure with improved lattice mismatch, characterized in that, Includes the following steps: Obtain a 111-sided single-crystal silicon substrate; A single-crystal boron nitride transition layer is epitaxially grown on the 111-plane single-crystal silicon substrate; the single-crystal boron nitride includes: 111 cubic boron nitride, hexagonal boron nitride, or boron-faceted wurtzite boron nitride. A diamond epitaxial layer is grown on the surface of the single-crystal boron nitride transition layer; The surface of the diamond epitaxial layer is subjected to nitrogen termination treatment to form a nitrogen-terminated surface; A single-crystal boron-aluminum nitrogen (BOA) with a donor impurity-doped Al-plane polar fibrous wurtzite structure is epitaxially grown on the nitrogen-terminated surface to form a BOA / nitrogen-terminated diamond two-dimensional electron gas heterojunction. During the BOA growth process, the boron and aluminum composition in the BOA epitaxial layer is controlled by adjusting the ratio of boron source to aluminum source.

2. The method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch according to claim 1, characterized in that, The nitrogen terminal treatment employs MBE, RIE, or ICP processes.

3. A method for preparing a boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure with improved lattice mismatch according to claim 1 or 2, characterized in that, In the process of forming the boron-aluminum-nitrogen epitaxial layer, trimethylaluminum, trimethylboron, and nitrogen are used as aluminum, boron, and nitrogen sources, respectively.

4. A boron-aluminum-nitrogen / diamond two-dimensional electron gas heterojunction structure for improving lattice mismatch, characterized in that, Prepared by the preparation method according to any one of claims 1-3, comprising: A 111-plane monocrystalline silicon substrate, a monocrystalline boron nitride transition layer on the 111-plane monocrystalline silicon substrate, a diamond epitaxial layer on the monocrystalline boron nitride transition layer, a nitrogen-terminated surface on the diamond epitaxial layer, and a boron-aluminum-nitrogen epitaxial layer with an Al-plane polar fibrous wurtzite structure doped with donor impurities on the nitrogen-terminated surface. The materials of the monocrystalline boron nitride transition layer include: 111 cubic boron nitride, hexagonal boron nitride, or boron-polarized fibrous wurtzite boron nitride.

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