AlGaN-based deep ultraviolet light emitting diode injection structure and application

Abstract

The invention discloses an AlGaN-based deep ultraviolet light emitting diode injection structure and an application thereof. The injection structure provided by the invention is a periodic structure, and each periodic structure comprises the following components: a p-AlmGa1-mN layer of which the proportion of an Al component is gradually changed; in each periodic structure, the proportion m of the Al component is linearly and gradually changed from x to y along the growth direction, and the value range of x is 0.6-0.85; the value range of y is 0.3 to 0.7; and xgt; y. The injection structure provided by the invention can modulate the p-type region energy band by utilizing the negative polarization body charge generated by inducing the piezoelectric polarization effect, thereby reducing the hole injection barrier and inhibiting the electron leakage. According to the method, the p-type region of the deep ultraviolet light-emitting device is integrated into a unified periodic structure, the use of an electron blocking layer (p-EBL) is avoided, the carrier injection efficiency of the device is improved, meanwhile, the working voltage of the device is effectively reduced, and the method has important significance for improving the electro-optical conversion efficiency of an AlGaN-based DUV-LED and promoting the industrial application of the AlGaN-based DUV-LED.

Description

Technical Field

[0001] The invention belongs to the technical field of deep ultraviolet light emitting diodes, and in particular relates to an injection structure of an AlGaN-based deep ultraviolet light emitting diode (DUV-LED) and an application thereof. Background Art

[0002] As a solid-state light source, AlGaN-based deep ultraviolet light-emitting diodes (DUV-LEDs) have significant advantages such as no mercury pollution, small size, low energy consumption, long life, and easy integration. They play an irreplaceable role in many fields such as sterilization and disinfection, environmental testing, communication detection, medical and health care, and are one of the core industries with great development prospects in the field of III-nitride semiconductors.

[0003] However, the current industrialization process of DUV-LED faces the bottleneck of low device electro-optical conversion efficiency. One of the main reasons why its performance is difficult to break through is the unbalanced carrier injection caused by the electron blocking layer (p-EBL) and the high operating voltage of the device, which is also a key technical problem that needs to be solved urgently at this stage.

[0004] Due to the small effective mass and high drift rate of electrons, after completing radiative recombination with holes, excess electrons can easily escape from the quantum well into the p-type region. In order to suppress electron leakage, high Al component AlGaN is usually used as the p-EBL layer between the DUV-LED quantum well and the p-type region, and its wide bandgap characteristics are used to form a very high potential barrier on the conduction band to block electrons. However, the existence of p-EBL, on the one hand, is also accompanied by the formation of a high potential barrier on the valence band, which brings great challenges to the injection of holes into the quantum well, resulting in serious imbalance in the transport of electrons and holes; on the other hand, due to the large bandgap width of p-EBL, the energy band step formed between it, the quantum well and p-AlGaN will introduce additional voltage drop, which will cause the device operating voltage to increase, and ultimately affect the performance of DUV-LED.

[0005] At present, there are two main technical solutions to solve the above problems: one is to optimize the configuration of p-EBL, modulate the band structure through the piezoelectric polarization effect, and reduce the hole injection barrier as much as possible while ensuring that p-EBL suppresses electron leakage, or increase the probability of holes tunneling through EBL. Another feasible solution is to achieve high-concentration effective doping of high-Al component p-AlGaN through methods such as polarization-induced doping or superlattice, so that p-AlGaN can participate in the device operation as a hole supply layer (replacing traditional p-GaN), thereby reducing the band gap between p-EBL and the hole supply layer and reducing the hole injection barrier.

[0006] Obviously, although the above two technical routes can optimize the carrier transport characteristics of the device to a certain extent, they cannot fundamentally eliminate the blocking of holes by p-EBL, the low carrier injection efficiency, and the high operating voltage problem caused by the existence of band steps. Therefore, the effect of improving device performance is very limited. Summary of the invention

[0007] In view of the above problems, the present invention provides a p-AlGaN integrated structure with periodic composition gradient, which can avoid the use of p-EBL, while improving the carrier injection efficiency, greatly reducing the device operating voltage, and further improving the electro-optical conversion efficiency of DUV-LED, thereby solving the problems of low carrier injection efficiency and high device operating voltage caused by EBL.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In the first aspect, the present invention provides an injection structure of an AlGaN-based deep ultraviolet light-emitting diode, which is a periodic structure, and each periodic structure includes the following components: p-Al with a gradient Al component ratio; m Ga 1-m N layers;

[0010] In each periodic structure, the Al component proportion m varies linearly from x to y along the growth direction, and the value range of x is 0.6-0.85, preferably 0.65-0.8; the value range of y is 0.3-0.7, preferably 0.45-0.65; and x>y.

[0011] In the above-mentioned injection structure, the thickness of each periodic structure is a, and the value range of a is 3-10 nm, preferably 4-8 nm.

[0012] In the above-mentioned injection structure, the thickness of the structure is n·a, n represents the number of periods, and the value range of n is 2-20, preferably 5-15.

[0013] In a second aspect, the present invention further provides a method for preparing the above-mentioned AlGaN-based deep ultraviolet light-emitting diode injection structure, comprising the following steps:

[0014] S1: Using the metal organic chemical vapor deposition (MOCVD) method, the flow rates of the Ga source and the Al source are adjusted to the initial values ​​respectively;

[0015] S2: Open the organic source gas path for epitaxial growth, and control the gradual gradient of the flow rate of Ga source and Al source to grow p-Al with a linear gradient of Al component ratio on the AlGaN-based quantum well sample. m Ga 1-m N film layer, which completes the first cycle of the integrated structure;

[0016] S3: close the organic source gas path and adjust the flow rates of the Ga source and the Al source to the initial values ​​in step S1;

[0017] S4: Repeat steps S2-S3 to obtain a p-Al with a periodic structure and linear gradient of Al composition. m Ga 1-m N integrated structure.

[0018] In step S1, the flow rate ratio of the Ga source and the Al source is controlled to meet the requirements of x and y in the above periodic structure.

[0019] In step S2, the gradient ratio of the flow rate of the Al source is controlled to meet the requirement of the linear relationship of the proportion of the Al component in the periodic structure.

[0020] In step S2, the growth time is controlled to meet the requirement of thickness a of the periodic structure.

[0021] In step S4, the number of repetitions is controlled to meet the requirement of the number of periods n of the periodic structure.

[0022] That is, in the above preparation method, the number of repetitions, the film thickness and the Al component gradient are selected according to the needs of the AlGaN-based deep ultraviolet light-emitting diode device, and the conditions are met: <x。

[0023] In a third aspect, the present invention further provides an AlGaN-based deep ultraviolet light-emitting diode device, which includes the above-mentioned AlGaN-based deep ultraviolet light-emitting diode injection structure.

[0024] Exemplarily, the AlGaN-based deep ultraviolet light-emitting diode device comprises, from bottom to top, the following structures:

[0025] Sapphire substrate;

[0026] AlN layer;

[0027] AlN / AlGaN multi-period stress modulation layer;

[0028] n-AlGaN layer;

[0029] AlGaN / AlGaN active region layer;

[0030] Periodic Al composition gradient p-AlGaN integrated structure;

[0031] p-GaN layer.

[0032] The beneficial effects achieved by the present invention are as follows:

[0033] 1. The present invention adopts a p-AlGaN integrated structure with periodic composition gradient, which plays a dual role of blocking electrons and promoting the longitudinal transport of holes, thereby avoiding the use of p-EBL, while improving the longitudinal transport capacity of carriers and eliminating the working partial pressure brought by p-EBL.

[0034] In terms of carrier transport, the present invention introduces the piezoelectric polarization effect through the gradual change of the Al component, induces the generation of negative polarized body charge inside the p-AlGaN, and modulates the energy band: on the one hand, the conduction band is raised to form a continuous high potential barrier, which plays a role in suppressing electron leakage, thereby replacing the p-EBL; on the other hand, the negative polarized charge can also effectively reduce the energy level position of the valence band. In the process of hole transport from the p-type region to the active region, it only needs to cross a smaller potential barrier and is not blocked by the p-EBL, so its injection efficiency can be greatly improved.

[0035] In terms of operating voltage, the structure integrates the p-type region, which can simplify the device configuration and eliminate the band steps introduced by p-EBL in traditional DUV-LEDs, thereby reducing the operating voltage.

[0036] 2. The p-AlGaN integrated structure with periodic component gradient provided by the present invention has a simple structure, has no strict requirements on the gradient, thickness and number of periods, has low requirements on growth, is easy to achieve in growth, is suitable for ultraviolet light-emitting devices of various wavelengths, has good applicability and practicality, and is suitable for vigorous promotion to the industrial application of deep ultraviolet light-emitting devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the gradual change of the Al component ratio during the growth of the p-AlGaN integrated structure with periodic component gradient provided by the present invention.

[0038] Figure 2 Schematic diagram of the overall structure of a DUV-LED including a p-AlGaN integrated structure with periodic composition gradient provided in Example 2.

[0039] Figure 3 This is a simulation verification result diagram of the internal quantum efficiency and power density of the DUV-LED with a p-AlGaN integrated structure having a periodic composition gradient provided in Example 2.

[0040] Figure 4 This is a diagram showing the simulation verification results of the current-voltage (IV) curve of the DUV-LED having a p-AlGaN integrated structure with periodic composition gradient provided in Example 2. DETAILED DESCRIPTION

[0041] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited to the following embodiments.

[0042] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods. Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can all be obtained from commercial sources.

[0043] The present invention specifically provides a periodically composition-graded p-AlGaN integrated structure for AlGaN-based deep ultraviolet light-emitting devices, and its preparation method specifically includes the following steps:

[0044] S1: By using the method of metalorganic chemical vapor deposition (MOCVD), adjust the flow rates of the metal sources (Ga source and Al source) to the initial values, corresponding to an AlGaN film with an Al component of x. x Ga 1-x N film;

[0045] S2: Open the organic source gas path for epitaxial growth. By controlling the flow rates of the metal sources, grow a p-AlGaN layer with a linearly gradually decreasing Al component from x to y on the AlGaN-based quantum well sample, as the first period of the integrated structure, with a thickness of a. The Al component y can be adjusted by adjusting the growth parameters, but it is necessary to satisfy the condition y < x; as Figure 1 shown;

[0046] S3: Close the organic source gas path and adjust the metal source flow rates to the initial values in S1;

[0047] S4: Repeat S2 - S3 (n - 1) times to obtain a composition-graded p-AlGaN integrated structure with a period number of n.

[0048] The key of the present invention lies in using the periodically Al-component-graded p-AlGaN to integrate the p-type region, avoiding the use of p-EBL, simplifying the device configuration, improving the carrier injection efficiency of DUV-LEDs and reducing the operating voltage.

[0049] Different Al-component gradient, thickness and period number have different improvement effects on the carrier transport ability and operating voltage. The present invention can control the Al-component gradient, single-period thickness and period number of the p-type integrated structure by controlling the metal source flow rates, growth time and cycle number, and then modulate the energy band structure and carrier transport behavior of the p-type region.

[0050] In the present invention, the p-type region plays a dual role of blocking electrons and promoting hole transport by using the periodic Al component gradient setting, weakening the function of p-EBL and replacing it, which is the core link of the present invention. Negative polarized body charge is introduced through the piezoelectric polarization effect, and a continuous high potential barrier is formed in the p-type conduction band region to suppress electron leakage, thereby achieving the purpose of replacing p-EBL; under this structure, hole injection will be free from the obstruction of p-EBL, and the barrier height of the p-type valence band region is reduced under the modulation of polarization charge, and the hole transport capacity will be greatly improved. At the same time, the integrated structure can eliminate the band step introduced by p-EBL, which plays a role in reducing the operating voltage.

[0051] In summary, the present invention integrates the p-type region and avoids the use of p-EBL by setting p-AlGaN with periodic Al composition gradient, which greatly improves the carrier transport capacity of AlGaN-based DUV-LED and effectively reduces the device operating voltage, thereby improving the device's electro-optical conversion efficiency.

[0052] Example 1 Periodic composition gradient p-AlGaN integrated structure and preparation

[0053] This embodiment provides a p-AlGaN integrated structure with periodic composition gradient, and the preparation method thereof includes:

[0054] S1: Using the metal organic chemical vapor deposition (MOCVD) method, the flow rate of the metal source (Ga source and Al source) is adjusted to the initial value, corresponding to the AlGaN material with a composition of 0.8 (i.e. Al 0.8 Ga 0.2 N);

[0055] S2: Open the organic source gas path for epitaxial growth. By controlling the flow rate of the metal source, a p-AlGaN layer with a linear gradient of Al composition from 0.8 to 0.55 is grown on the AlGaN-based quantum well sample as the first period of the integrated structure with a thickness of 6 nm.

[0056] S3: Close the organic source gas line and adjust the metal source flow rate to the initial value in S1;

[0057] S4: Repeat S2-S3 7 times to obtain a composition-gradient p-AlGaN integrated structure with 8 periods.

[0058] Example 2 Preparation of DUV-LED using p-AlGaN integrated structure with periodic composition gradient

[0059] like Figure 2 As shown, this embodiment provides a method for preparing a DUV-LED using a p-AlGaN integrated structure with periodic composition gradient, comprising:

[0060] S1: growing a 2 μm thick AlN layer on a sapphire substrate using MOCVD;

[0061] S2: growing 100 cycles of AlN / AlGaN stress modulation layer on the AlN layer;

[0062] S3: Growing 1μm thick Si-doped Al on the superlattice stress buffer layer 0.55 Ga 0.45 The N layer serves as an n-type layer;

[0063] S4: In n-type Al 0.55 Ga 0.45 A 10nm thick Al layer is grown on the N layer. 0.5 Ga 0.5 N layer, as the first layer of quantum barrier;

[0064] S5: Grow a 2nm thick Al layer on the quantum barrier 0.35 Ga 0.65 N layer, as a quantum well layer;

[0065] S6: Repeat S4-S5 4 times to obtain 5 pairs of quantum wells;

[0066] S7: Repeat S4 as the last quantum barrier to complete the growth of the active region;

[0067] S8: Adjust the flow rate of the metal source (Ga source and Al source) so that it corresponds to the AlGaN material with a composition of 0.8 (i.e. Al 0.8 Ga 0.2 N);

[0068] S9: Open the organic source gas path, and by controlling the flow rate of the metal source, grow a p-AlGaN layer with a linear gradient of Al composition from 0.8 to 0.55 on the AlGaN-based quantum well sample as the first period of the integrated structure, with a thickness of 6 nm;

[0069] S10: Close the organic source gas line and adjust the metal source flow rate to the initial value in S8;

[0070] S11: Repeat S9-S10 7 times to complete the growth of the composition-gradient p-AlGaN integrated structure with 8 cycles.

[0071] S12: growing a 10 nm thick Mg-doped p-GaN layer on the p-type integrated structure as a top ohmic contact layer.

[0072] Effect verification

[0073] Taking a conventional DUV-LED structure including p-EBL and constant-composition p-AlGaN as a comparative example, the difference between the conventional DUV-LED structure obtained in Example 2 is that between the AlGaN / AlGaN active region layer and the p-GaN layer are: p-EBL layer, constant-composition p-AlGaN layer.

[0074] The AlGaN-based DUV-LED structure obtained in Example 2 and the DUV-LED structure including p-EBL and constant-composition p-AlGaN were tested and compared using a simulation method, and the results are as follows:

[0075] (1) Figure 3 As shown, the current density is 0-100A / cm 2 When the maximum internal quantum efficiency of the AlGaN-based DUV-LED obtained in Example 2 is increased by 29.7% compared with the conventional structure;

[0076] (2) Figure 3 As shown, the current density is 0-100A / cm 2 When the maximum light output power density of the AlGaN-based DUV-LED obtained in Example 2 is increased by 37.0% compared with the traditional structure.

[0077] (3) Figure 4 As shown, the current density is 100A / cm 2 The operating voltage of the AlGaN-based DUV-LED obtained in Example 2 is reduced by 0.4 V compared with the traditional structure.

[0078] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

Claims

1. An injection structure of an AlGaN-based deep ultraviolet light-emitting diode, which is a periodic structure, each periodic structure includes the following components: p-Al with a gradient Al component ratio m Ga 1-m N layers; In each periodic structure, the Al component proportion m changes linearly from x to y along the growth direction, with x ranging from 0.6 to 0.85; y ranging from 0.3 to 0.7; and x>y.

2. The AlGaN-based deep ultraviolet light-emitting diode injection structure according to claim 1, characterized in that: The thickness of each periodic structure is a, and the value range of a is 3-10 nm.

3. The AlGaN-based deep ultraviolet light-emitting diode injection structure according to claim 1 or 2, characterized in that: The thickness of the injection structure is n·a; n represents the number of cycles, and the value range of n is 2-20.

4. The AlGaN-based deep ultraviolet light-emitting diode injection structure according to any one of claims 1 to 3, characterized in that: The x value range is 0.65-0.8, the y value range is 0.45-0.65, the a value range is 4-8nm, and the n value range is 5-15.

5. A method for preparing an injection structure of an AlGaN-based deep ultraviolet light-emitting diode according to any one of claims 1 to 4, comprising the following steps: S1: Using the metal organic chemical vapor deposition method, the flow rates of the Ga source and the Al source are adjusted to the initial values ​​respectively; S2: Open the organic source gas path for epitaxial growth, and control the gradual gradient of the flow rate of Ga source and Al source to grow p-Al with a linear gradient of Al component ratio on the AlGaN-based quantum well sample. m Ga 1-m N film layer, which completes the first cycle of the integrated structure; S3: close the organic source gas path and adjust the flow rates of the Ga source and the Al source to the initial values ​​in step S1; S4: Repeat steps S2-S3 to obtain a p-Al with a periodic structure and linear gradient of Al composition. m Ga 1-m N integrated structure.

6. The preparation method according to claim 5, characterized in that: In step S1, the flow rate ratio of the Ga source and the Al source is controlled to meet the requirements of x and y in each periodic structure.

7. The preparation method according to claim 5 or 6, characterized in that: In step S2, the gradient ratio of the flow rate of the Al source is controlled to meet the requirement of the linear relationship of the proportion of the Al component in each periodic structure.

8. The preparation method according to any one of claims 5 to 7, characterized in that: In step S2, the growth time is controlled to meet the requirement of thickness a of each periodic structure.

9. The preparation method according to any one of claims 5 to 8, characterized in that: In step S4, the number of repetitions is controlled to meet the requirement of the number of periods n of each periodic structure.

10. An AlGaN-based deep ultraviolet light-emitting diode device, comprising the injection structure of the AlGaN-based deep ultraviolet light-emitting diode according to any one of claims 1 to 4.

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