A method for preparing a wavelength-controllable AlGaN-based ultraviolet light-emitting device

Abstract

This invention discloses a method for fabricating wavelength-controllable AlGaN-based ultraviolet light-emitting devices, belonging to the field of semiconductor optoelectronic devices. During quantum well growth, while maintaining a constant Al and Ga source supply ratio and growth temperature, the method regulates the ammonia flow rate to control the desorption and incorporation of Ga atoms into the quantum well, thereby adjusting the actual incorporation amount of Ga atoms and altering the effective composition and band structure of the quantum well. This allows for precise control of the emission wavelength of the quantum well's light-emitting layer. This invention solves technical problems such as reduced luminous efficiency, wavelength drift, and poor device stability. The method is simple and easy to control, significantly improving device consistency and production stability, laying the foundation for technological advancements in AlGaN-based ultraviolet light-emitting devices. It represents a crucial step towards large-scale and stable industrial production for applications such as encrypted communication, pure water purification, and biomedicine. This invention is applicable to ultraviolet light-emitting diodes and ultraviolet laser diodes.

Description

Technical Field

[0001] This invention relates to semiconductor optoelectronic devices, and more specifically to a method for fabricating a wavelength-controllable AlGaN-based ultraviolet light-emitting device. Background Technology

[0002] AlGaN-based ultraviolet light-emitting devices have broad application prospects in fields such as efficient sterilization, encrypted communication, biomedicine, and military defense due to their advantages of small size, low cost, long lifetime, and ease of integration. The structure of these devices typically includes a substrate, a buffer layer, a light-emitting layer, and electrode structures. The light-emitting layer usually consists of one or more AlGaN quantum wells and barrier structures, and its band structure directly determines the emission wavelength, thus significantly impacting the device's application performance and applicable scenarios.

[0003] Currently, band structure modulation mainly relies on altering the supply ratio of group III sources and the growth temperature during epitaxial growth. However, these methods still face numerous challenges in controlling the emission wavelength. Specifically, when controlling the emission wavelength by changing the supply ratio of group III sources, the surface mobility of Al atoms is significantly lower than that of Ga atoms, limiting their diffusion and migration capabilities during growth. This can easily lead to problems such as inhomogeneous alloy composition and rough interfaces, making it difficult to achieve precise control of the emission wavelength and thus affecting the repeatability and stability of the device.

[0004] On the other hand, when the emission wavelength is controlled by changing the growth temperature, a high growth temperature can easily cause Ga atom desorption, while a low growth temperature may lead to a decrease in the interface quality of the AlGaN emitting layer, which in turn can cause problems such as reduced luminous efficiency, wavelength drift and deterioration of device stability.

[0005] Therefore, there is an urgent need for a new method for wavelength modulation of AlGaN-based ultraviolet light-emitting devices, which can achieve stable and repeatable adjustment of the emission wavelength of the device without significantly increasing the complexity of the process, so as to meet the needs of different application scenarios. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention proposes a method for fabricating AlGaN-based ultraviolet light-emitting devices with controllable wavelength. This method achieves precise and repeatable control of the wavelength of AlGaN-based ultraviolet light-emitting devices simply by adjusting the flow rate of ammonia in the light-emitting layer, without changing the supply ratio of group III source or the growth temperature. This meets the wavelength requirements of ultraviolet light-emitting devices in different application scenarios and also lays the foundation for the technological advancement of devices such as ultraviolet light-emitting diodes and laser diodes.

[0007] The method for fabricating a wavelength-controllable AlGaN-based ultraviolet light-emitting device according to the present invention includes the following steps:

[0008] 1) Provide a substrate and grow a buffer layer on the substrate;

[0009] 2) Grow a transition layer on the buffer layer;

[0010] 3) Growing multi-period superlattice thin film layers on the transition layer;

[0011] 4) n-AlGaN is grown on a superlattice thin film layer. During the growth of n-AlGaN, the Al source is periodically switched on and off to form an n-type electron injection layer.

[0012] 5) Ammonia-controlled quantum well light-emitting layer is grown on an n-type electron injection layer. During the growth of the quantum well, the supply ratio of Al source and Ga source and the growth temperature are kept constant. The flow rate of ammonia is controlled to change the nitrogen chemical potential and active nitrogen coverage on the growth surface of the quantum well, thereby controlling the behavior of Ga atom desorption and incorporation into the quantum well and adjusting the actual amount of Ga atom incorporation in the quantum well. The change in the actual amount of Ga atom incorporation causes changes in the effective composition and band structure of the quantum well, thereby finely controlling the emission wavelength of the quantum well.

[0013] 6) Continue to grow the p-type AlGaN structure of the AlGaN-based ultraviolet light-emitting device on the quantum well light-emitting layer to obtain the AlGaN-based ultraviolet light-emitting device.

[0014] In step 1), the substrate is a sapphire substrate, a silicon carbide substrate, or a silicon substrate, and the substrate is placed in the growth chamber of the epitaxial growth equipment. The epitaxial equipment is a metal-organic chemical vapor deposition (MOCVD) equipment or a molecular beam epitaxial chemical vapor deposition (MBE) equipment. The buffer layer is made of AlN or AlGaN, with a thickness of 30~200 nm, a growth temperature of 750~1050℃, and a growth pressure of 100~200 Torr.

[0015] In step 2), the transition layer is made of AlN with a thickness of 0.1~1.5μm, a growth temperature of 1150~1350℃, and a growth pressure of 30~50 Torr.

[0016] In step 3), the multi-period superlattice thin film layer comprises two materials: AlGaN or AlN / GaN with different Al compositions; the number of periods in the superlattice thin film layer is 50–150. For the two AlGaN materials with different Al compositions, one AlGaN has a thickness of 1–3 nm and an Al composition of 75%–95%; the other AlGaN has a thickness of 0.5–2 nm and an Al composition of 50%–70%; the growth temperature is 1000–1180 °C, and the growth pressure is 30–50 Torr. For AlN / GaN, the AlN has a thickness of 1–3 nm, the GaN has a thickness of 1–3 nm, the growth temperature is 1050–1130 °C, and the growth pressure is 30–50 Torr.

[0017] In step 4), the growth of the n-type electron injection layer includes multiple Al source on / off cycles, with a cycle number of 80-200. Each Al source on / off cycle includes an Al source turn-on time of 10-200 s and an Al source turn-off time of 5-20 s. During the Al source turn-on time, the Al source flow rate remains constant at 140-300 sccm. The growth temperature is 1050-1250℃, and the growth pressure is 30-50 Torr. The thickness of the n-type electron injection layer is 0.2-8 μm, and the Al composition is 50%-65%. N-type conductivity is achieved by doping with SiH4, with a SiH4 doping concentration of 8 × 10⁻⁶ g / L. 18 ~2×10 19 cm -3 .

[0018] In step 5), the quantum well light-emitting layer comprises a multi-period quantum barrier and a quantum well, with a period number of 1 to 8. The thickness of the quantum barrier is 9 to 15 nm, and the growth temperature is 1050 to 1250 °C. The thickness of the quantum well is 0.1 to 3 nm, and the growth temperature is 1050 to 1250 °C. Specifically, the Al composition of the quantum barrier and the quantum well is 20% to 50%, with the Al composition of the quantum barrier being greater than that of the quantum well. The ammonia flow rate is adjusted from 3 to 100 slm to control the emission wavelength of the AlGaN-based ultraviolet light-emitting device. During the epitaxial growth of the quantum well light-emitting layer, the actual amount of Ga atoms incorporated into the quantum well is not only related to the supply of the group III source but is also significantly affected by the nitrogen chemical potential and active nitrogen coverage on the growth surface. Under high-temperature growth conditions, the desorption and incorporation processes of Ga atoms are in a dynamic competitive equilibrium. In this invention, while maintaining a constant Al / (Al+Ga) source supply ratio and growth temperature, the Al / (Al+Ga) supply ratio is 20%–55%. By adjusting the ammonia flow rate, the nitrogen chemical potential and active nitrogen coverage of the quantum well growth surface are altered, thereby controlling the desorption and incorporation behavior of Ga atoms. When the ammonia flow rate increases, the active nitrogen coverage of the growth surface improves, which is beneficial for Ga-N bond formation, thus inhibiting Ga atom desorption and allowing more Ga atoms to be incorporated into the quantum well. When the ammonia flow rate decreases, the active nitrogen supply to the growth surface is relatively insufficient, making Ga atoms more prone to desorption, resulting in a decrease in the actual incorporation amount of Ga atoms in the quantum well. Under constant Al / Ga source supply ratio and growth temperature, changes in the actual incorporation amount of Ga atoms cause changes in the effective composition and band structure of the quantum well, leading to changes in the quantum well emission wavelength. Specifically, under the conditions of constant Al / Ga source supply ratio and growth temperature, as the ammonia flow rate increases, the emission wavelength of the quantum well shifts towards longer wavelengths; as the ammonia flow rate decreases, the emission wavelength of the quantum well shifts towards shorter wavelengths. When the A1 composition of the quantum well is 45%~55%, the ammonia flow rate can be adjusted from 3slm to 100slm to achieve continuous tunability in the range of approximately 260~280nm; when the A1 composition of the quantum well is 20%~45%, the ammonia flow rate can be adjusted from 3slm to 100slm to achieve continuous tunability in the range of approximately 280~310nm.

[0019] In step 6), the AlGaN-based ultraviolet light-emitting device includes an ultraviolet light-emitting diode (UV LED) and an ultraviolet laser diode. The p-type AlGaN structure of the UV LED includes: a p-type electron blocking layer, a p-type hole injection layer, and a p-type ohmic contact layer; the p-type electron blocking layer is made of p-AlGaN, with a thickness of 10–30 nm, an Al composition of 0.8–1.0, a growth temperature of 1150–1250 °C, and a growth pressure of 35–55 Torr. P-type conductivity is achieved by doping with Cp₂Mg, with a Cp₂Mg vapor phase doping concentration of 8 × 10⁻⁶.19 ~3×10 20 cm -3 The p-type hole injection layer is made of p-AlGaN, with a thickness of 30–100 nm and an Al composition of 0.35–0.60. The growth temperature is 1050–1150 °C, and the growth pressure is 35–55 Torr. P-type conductivity is achieved by doping with Cp₂Mg, with a Cp₂Mg vapor phase doping concentration of 1.5 × 10⁻⁶. 19 ~2×10 20 cm -3 The p-type ohmic contact layer is made of p-GaN with a thickness of 10–30 nm, grown at a temperature of 900–1000 °C and a growth pressure of 100–200 Torr. P-type conductivity is achieved by doping with Cp₂Mg, with a Cp₂Mg vapor phase doping concentration of 2.0 × 10⁻⁶. 20 ~5.0×10 20 cm -3 The p-type AlGaN structure of the ultraviolet laser diode includes: a p-type waveguide layer, a p-type electron blocking layer, a p-type hole injection layer, and a p-type ohmic contact layer; n-type and p-type waveguide layers are fabricated on the lower and upper surfaces of the quantum well light-emitting layer, respectively, with materials n-AlGaN and p-AlGaN, respectively; and a p-type electron blocking layer, a p-type hole injection layer, and a p-type ohmic contact layer are further fabricated on the p-type waveguide layer.

[0020] Advantages of this invention:

[0021] (1) Unlike the method of changing the supply of group III source, the present invention can achieve fine control of the wavelength of AlGaN-based ultraviolet light-emitting device with high repeatability;

[0022] (2) Unlike the method of changing the growth temperature, the quantum well interface grown by the present invention has better quality, which significantly improves the device performance and can improve the control accuracy of the emission wavelength to within 1 nanometer.

[0023] (3) The method is simple and easy to control, which significantly improves production stability and lays the foundation for the technological progress of ultraviolet light-emitting diodes and laser diodes; it has taken a key step towards large-scale and stable industrial production in applications such as encrypted communication, pure water purification and biomedicine.

[0024] This invention introduces the flow rate of ammonia as a controllable process parameter, enabling precise control of the wavelength of AlGaN-based ultraviolet light-emitting devices while maintaining stable epitaxial growth conditions, thereby improving device consistency and production stability. This invention is applicable to ultraviolet light-emitting diodes and laser diodes. Attached Figure Description

[0025] Figure 1This is a cross-sectional view of an embodiment of the wavelength-controllable AlGaN-based ultraviolet light-emitting device of the present invention;

[0026] Figure 2 X-ray diffraction test pattern of an embodiment of the wavelength-controllable AlGaN-based ultraviolet light-emitting device of the present invention;

[0027] Figure 3 This is a schematic diagram showing the relationship between the emission spectrum and ammonia flow rate of an embodiment of the wavelength-controllable AlGaN-based ultraviolet light-emitting device of the present invention. Detailed Implementation

[0028] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0029] In this embodiment, an ultraviolet light-emitting diode (UV LED) is fabricated. A schematic diagram of the UV LED structure is shown below. Figure 1 As shown.

[0030] The method for fabricating a wavelength-controllable AlGaN-based ultraviolet light-emitting device in this embodiment includes the following steps:

[0031] 1) Provide a silicon carbide substrate 1 and place the silicon carbide substrate in the growth chamber of MOCVD; grow a 50nm thick AlN on the silicon carbide substrate at a growth temperature of 1040℃ and a growth pressure of 120Torr to form a buffer layer 2.

[0032] 2) A 1.0 μm thick AlN layer was grown on the buffer layer at a growth temperature of 1250℃ and a growth pressure of 30 Torr to form a transition layer 3;

[0033] 3) A superlattice thin film layer 4 is grown on the transition layer. The superlattice thin film layer has 120 cycles. In one cycle, one type of AlGaN has a thickness of 1.5 nm and an Al composition of 85%, and another type of AlGaN has a thickness of 1.5 nm and an Al composition of 65%. The growth temperature is 1100℃ and the growth pressure is 30 Torr.

[0034] 4) n-AlGaN was grown on a superlattice thin film, including 120 Al source on / off cycles. Each Al source on / off cycle included an Al source turn-on time of 110 s and an Al source turn-off time of 13 s. During the Al source turn-on time, the Al source flow rate was maintained at 295 sccm. The growth temperature was 1100℃, and the growth pressure was 30 Torr. The thickness was 5 μm, and the Al composition was 58%. n-type conductivity was achieved by doping with SiH4, with a SiH4 doping concentration of 1 × 10⁻⁶ vapor phase. 19 cm -3 5 n-type electron injection layers;

[0035] 5) An ammonia-controlled quantum well light-emitting layer 6 was grown on the n-type electron injection layer; the quantum well light-emitting layer consisted of 5 periods of quantum barriers and quantum wells, the thickness of the quantum barriers was 10 nm, the Al composition was 50%, and the growth temperature was 1100 °C; the thickness of the quantum wells was 1.4 nm, the Al composition was 25%, and the growth temperature was 1100 °C; X-ray diffraction tests were performed on the device, from... Figure 2 It can be seen that the quantum well exhibits five sharp satellite peaks, namely... Figure 2 The interfaces a, b, c, d, and e are marked in the figure; when the ammonia flow rate of the quantum well is adjusted from 3 slm to 100 slm, the emission wavelength can be continuously adjusted from 280 nm to 310 nm, as shown in the figure. Figure 3 As shown.

[0036] 6) A p-type electron blocking layer 7, 25 nm thick with an Al composition of 0.85, was formed by growing p-AlGaN on the quantum well light-emitting layer. The growth temperature was 1180 °C and the growth pressure was 45 Torr. P-type conductivity was achieved by doping with Cp2Mg, with a Cp2Mg vapor phase doping concentration of 1 × 10⁻⁶. 20 cm -3 A p-type hole injection layer 8 with a thickness of 70 nm and an Al composition of 0.45 was formed by growing p-AlGaN on a p-type electron blocking layer. The growth temperature was 1080 °C and the growth pressure was 35 Torr. P-type conductivity was achieved by doping with Cp2Mg, with a Cp2Mg vapor phase doping concentration of 1.5 × 10⁻⁶. 20 cm -3 A p-type ohmic contact layer 9 with a thickness of 15 nm was formed by growing p-GaN on the p-type hole injection layer at a growth temperature of 920℃ and a growth pressure of 150 Torr. P-type conductivity was achieved by doping with Cp₂Mg at a vapor phase concentration of 2.5 × 10⁻⁶. 20 cm -3 .

[0037] Finally, it should be noted that the purpose of disclosing the embodiments is to help further understand the present invention. However, those skilled in the art will understand that various substitutions and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the present invention should not be limited to the content disclosed in the embodiments, and the scope of protection of the present invention is defined by the claims.

Claims

1. A method for fabricating a wavelength-controllable AlGaN-based ultraviolet light-emitting device, characterized in that, The preparation method includes the following steps: 1) Provide a substrate and grow a buffer layer on the substrate; 2) Grow a transition layer on the buffer layer; 3) Growing multi-period superlattice thin film layers on the transition layer; 4) n-AlGaN is grown on a superlattice thin film layer. During the growth of n-AlGaN, the Al source is periodically switched on and off to form an n-type electron injection layer. 5) Grow a quantum well light-emitting layer with ammonia control on an n-type electron injection layer; during the growth of the quantum well, keep the supply ratio of Al source and Ga source and the growth temperature constant, control the flow rate of ammonia, adjust the actual incorporation of Ga atoms in the quantum well, change the effective composition and band structure of the quantum well, and control the emission wavelength of the quantum well. 6) Continue to grow the p-type AlGaN structure of the AlGaN-based ultraviolet light-emitting device on the quantum well light-emitting layer to obtain the AlGaN-based ultraviolet light-emitting device.

2. The preparation method according to claim 1, characterized in that, In step 1), the substrate is a sapphire substrate, a silicon carbide substrate, or a silicon substrate; the buffer layer is made of AlN or AlGaN, with a thickness of 30~200nm, a growth temperature of 750~1050℃, and a growth pressure of 100~200Torr.

3. The preparation method according to claim 1, characterized in that, In step 2), the transition layer is made of AlN with a thickness of 0.1~1.5μm, a growth temperature of 1150~1350℃, and a growth pressure of 30~50Torr.

4. The preparation method according to claim 1, characterized in that, In step 3), the multi-period superlattice thin film layer includes two materials, namely AlGaN or AlN / GaN with different Al compositions; the number of periods of the superlattice thin film layer is 50 to 150.

5. The preparation method according to claim 1, characterized in that, In step 4), the growth of the n-type electron injection layer includes multiple Al source on / off cycles, with the number of cycles being 80 to 200; one Al source on / off cycle includes an Al source turn-on time and an Al source turn-off time, with the Al source turn-on time being 10 to 200 s and the Al source turn-off time being 5 to 20 s.

6. The preparation method according to claim 1, characterized in that, In step 4), the growth temperature of the n-type electron injection layer is 1050~1250℃, the growth pressure is 30~50 Torr, the thickness of the n-type electron injection layer is 0.2~8μm, and the Al composition is 50%~65%.

7. The preparation method according to claim 1, characterized in that, In step 5), the quantum well light-emitting layer includes a multi-period quantum barrier and a quantum well, with a period number of 1 to 8, a thickness of 9 to 15 nm for the quantum barrier, a growth temperature of 1050 to 1250 °C, a thickness of 0.1 to 3 nm for the quantum well, and a growth temperature of 1050 to 1250 °C; the Al composition of the quantum barrier and the quantum well is 20% to 50%, and the Al composition of the quantum barrier is greater than that of the quantum well.

8. The preparation method according to claim 1, characterized in that, In step 5), the flow rate of ammonia is adjusted from 3 to 100 slm to control the emission wavelength of the AlGaN-based ultraviolet light-emitting device.

9. The preparation method according to claim 8, characterized in that, As the ammonia flow rate increases, the emission wavelength shifts towards longer wavelengths; as the ammonia flow rate decreases, the emission wavelength shifts towards shorter wavelengths.

10. The preparation method according to claim 1, characterized in that, AlGaN-based ultraviolet light-emitting devices include ultraviolet light-emitting diodes and ultraviolet laser diodes.

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