Epitaxial structure of ultraviolet light-emitting device and preparation method thereof, ultraviolet light-emitting device

Abstract

The present invention relates to an epitaxial structure of an ultraviolet light-emitting device, a method for preparing the same, and an ultraviolet light-emitting device, belonging to the field of semiconductor technology. The structure comprises a substrate, an AlN layer, an n-type electron transport layer, a multi-quantum well light-emitting layer, an electron blocking layer, a p-type hole transport layer, and a p-type contact layer, which are grown sequentially from bottom to top. The p-type hole transport layer comprises at least one polarity change layer and a metal polarity layer. The polarity change layer comprises a polarity gradient layer and a polarity reversal layer grown on the polarity gradient layer. The metal polarity layer is grown on the polarity reversal layer of the topmost polarity change layer. The polarity gradient layer gradually changes from metal polarity to nitrogen polarity from bottom to top, and the polarity reversal layer changes from nitrogen polarity to metal polarity from bottom to top. The present invention can increase the hole carrier concentration and longitudinal migration rate, reduce the resistivity of the p-type hole transport layer, and thereby improve the photoelectric conversion efficiency of the ultraviolet light-emitting device.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an epitaxial structure of an ultraviolet light-emitting device and a preparation method thereof, and an ultraviolet light-emitting device. Background Art

[0002] Ultraviolet light-emitting devices have the advantages of environmental protection, energy saving, and single luminous wavelength, and can be used in sterilization, disinfection, biological detection and other aspects.

[0003] In the epitaxial structure of existing ultraviolet light-emitting devices, the p-type hole transport layer mainly adopts a single-component p-type AlGaN thin layer. The hole concentration of the p-type hole transport layer of this structure is low, which makes the resistivity of this layer high. In order to increase the hole concentration, there is currently a technology that uses the AlGaN superlattice method to obtain a higher in-plane carrier concentration and a higher migration rate. However, the barrier difference between the well barriers of the superlattice makes the hole migration rate in the longitudinal direction (towards the quantum well) poor, resulting in fewer holes actually entering the quantum well. In addition, there is also a pAlGaN layer with a gradient of Al composition from high to low as the p-type hole transport layer. This structure can polarize and induce a certain amount of hole carriers and realize the transmission of hole carriers in the longitudinal direction. However, this method is not large enough because the difference in polarization strength between AlN and GaN is not large enough, which makes the hole carriers induced by polarization limited.

[0004] In summary, the epitaxial structure of current ultraviolet light-emitting devices has problems such as low hole carrier concentration, low longitudinal migration rate of hole carriers and high resistivity of p-type hole transport layer, which leads to low photoelectric conversion efficiency of current ultraviolet light-emitting devices. Summary of the Invention

[0005] To solve the above technical problems, the present invention provides an epitaxial structure of an ultraviolet light-emitting device and a method for preparing the same, as well as an ultraviolet light-emitting device. The technical solution of the present invention is as follows:

[0006] In a first aspect, an epitaxial structure of an ultraviolet light-emitting device is provided, which includes a substrate, an AlN layer, an n-type electron transport layer, a multi-quantum well light-emitting layer, an electron blocking layer, a p-type hole transport layer, and a p-type contact layer grown sequentially from bottom to top;

[0007] The p-type hole transport layer includes at least one group of polarity change layers and metal polarity layers, the polarity change layer includes a polarity gradient layer and a polarity reversal layer grown on the polarity gradient layer, the metal polarity layer grows on the polarity reversal layer of the topmost polarity change layer, the polarity gradient layer gradually changes from metal polarity to nitrogen polarity from bottom to top, and the polarity reversal layer changes from nitrogen polarity to metal polarity from bottom to top.

[0008] Optionally, in a set of polarity change layers, the thickness of the polarity gradient layer is 1-500 nm, and the thickness of the polarity reversal layer is 0.1-10 nm.

[0009] Optionally, the Si doping concentration of the n-type electron transport layer is 1×10 18 -1×10 20 cm -3 .

[0010] Optionally, the Al component content in the polarity gradient layer remains unchanged, or the Al component content changes from high to low from bottom to top.

[0011] Optionally, in the polarity gradient layer, the Mg doping concentration increases from 1×10 20 cm -3 Gradient to 1×10 21 cm -3 ; In the metal polar layer, the Mg doping concentration is 1×10 18 -1×10 20 cm -3 .

[0012] Optionally, the thickness of the AlN layer is 100-5000 nm, the thickness of the n-type electron transport layer is 100-5000 nm, the thickness of the electron blocking layer is 1-50 nm, the thickness of the p-type hole transport layer is 10-200 nm, and the thickness of the p-type contact layer is 1-100 nm.

[0013] Optionally, the Al component content of the electron blocking layer is 0.4-1.0, and the Al component content of the p-type hole transport layer is 0.4-1.0; the number of periods of the multi-quantum well light-emitting layer is 1-10, the barrier layer thickness is 3-50nm, the Al component content is 0.4-0.7, the well layer thickness is 1-5nm, and the Al component content is 0.3-0.6.

[0014] In a second aspect, a method for preparing an epitaxial structure of an ultraviolet light-emitting device is provided, wherein the epitaxial structure of the ultraviolet light-emitting device is the epitaxial structure of the ultraviolet light-emitting device described in the first aspect above, and the preparation method comprises:

[0015] S1, growing an AlN layer on a substrate;

[0016] S2, growing an n-type electron transport layer on the AlN layer;

[0017] S3, growing a multi-quantum well light-emitting layer on the n-type electron transport layer;

[0018] S4, growing an electron blocking layer on the multi-quantum well light-emitting layer;

[0019] S5, growing a p-type hole transport layer on the electron blocking layer;

[0020] S6, growing a p-type contact layer on the p-type hole transport layer.

[0021] Optionally, the S5 includes: sequentially growing at least one set of polarity change layers and metal polarity layers from bottom to top, and sequentially growing a polarity gradient layer and a polarity reversal layer from bottom to top when growing each set of polarity change layers.

[0022] In a third aspect, an ultraviolet light-emitting device is provided, which includes the epitaxial structure of the ultraviolet light-emitting device described in the first aspect.

[0023] All the above optional technical solutions can be combined arbitrarily, and the present invention does not provide detailed descriptions of the structures after each combination.

[0024] By means of the above solution, the beneficial effects of the present invention are as follows:

[0025] By setting a p-type hole transport layer including at least one group of polarity change layers and metal polarity layers, the polarity change layer includes a polarity gradient layer and a polarity reversal layer grown on the polarity gradient layer, the metal polarity layer grows on the polarity reversal layer of the topmost polarity change layer, the polarity gradient layer gradually changes from metal polarity to nitrogen polarity from bottom to top, and the polarity reversal layer changes from nitrogen polarity to metal polarity from bottom to top. Since the metal polarity and nitrogen polarity surfaces have polarization field strengths with opposite polarization directions, the polarization intensity difference of the polarity gradient layer is large, so that after the polarity gradient layer induces more hole carriers, the hole carriers tunnel through the polarization reversal layer, thereby increasing the hole carrier concentration and longitudinal migration rate, reducing the resistivity of the p-type hole transport layer, and further improving the photoelectric conversion efficiency of the ultraviolet light-emitting device.

[0026] The above description is only an overview of the technical solution of the present invention. In order to more clearly understand the technical means of the present invention and implement it according to the contents of the specification, the following is a detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a structural schematic diagram of the epitaxial structure of the ultraviolet light-emitting device provided by an embodiment of the present invention.

[0028] Figure 2 It is a schematic structural diagram of a p-type hole transport layer provided by one embodiment of the present invention.

[0029] Figure 3 Schematic diagram of the structure of a p-type hole transport layer provided by another embodiment of the present invention. DETAILED DESCRIPTION

[0030] The following embodiments of the present invention are described in further detail with reference to the accompanying drawings and examples. The following examples are used to illustrate the present invention but are not intended to limit the scope of the present invention.

[0031] like Figures 1 to 3 As shown, an embodiment of the present invention provides an epitaxial structure of an ultraviolet light-emitting device, which includes a substrate 1, an AlN layer 2, an n-type electron transport layer 3, a multi-quantum well light-emitting layer 4, an electron blocking layer 5, a p-type hole transport layer 6 and a p-type contact layer 7 grown sequentially from bottom to top;

[0032] The p-type hole transport layer 6 includes at least one group of polarity change layers and a metal polarity layer 6-3, the polarity change layer includes a polarity gradient layer 6-1 and a polarity reversal layer 6-2 grown on the polarity gradient layer 6-1, the metal polarity layer 6-3 grows on the polarity reversal layer 6-2 of the topmost polarity change layer, the polarity gradient layer 6-1 gradually changes from metal polarity to nitrogen polarity from bottom to top, and the polarity reversal layer 6-2 changes from nitrogen polarity to metal polarity (aluminum polarity) from bottom to top.

[0033] The substrate 1 can be a sapphire substrate; the n-type electron transport layer 3 is an n-type doped AlGaN layer; the electron blocking layer 5 is an AlGaN layer; the p-type hole transport layer 6 is a p-type doped AlGaN layer; and the p-type contact layer 7 is a p-type doped GaN layer. In each of these layers, the sources of Ga are trimethylgallium and triethylgallium, the source of Al is trimethylaluminum, and the source of N is ammonia. Silane and bismuth magnesium serve as n-type and p-type dopants, respectively.

[0034] Specifically, the lower surface of the graded polarity layer 6-1 is a metal polarity surface, and the upper surface is a nitrogen polarity surface. The polarity of the upper and lower surfaces of the polarity reversal layer 6-2 is opposite. Because the metal polarity surface and the nitrogen polarity surface have polarization field strengths with opposite polarization directions, the polarization intensity difference of the graded polarity layer 6-1 is large. In turn, after the graded polarity layer 6-1 induces a large number of hole carriers, the hole carriers tunnel through the polarization reversal layer 6-2, thereby increasing the hole carrier concentration and longitudinal migration rate, reducing the resistivity of the p-type hole transport layer, and thus improving the photoelectric conversion efficiency of the ultraviolet light-emitting device. The provision of the metal polarity layer 6-3 can ensure the quality of the p-type contact layer grown thereon.

[0035] In a specific embodiment, the p-type hole transport layer 6 includes a set of polarity change layers and metal polarity layers 6-3, such as Figure 2 In another specific embodiment, the p-type hole transport layer 6 includes several groups of polarity change layers and metal polarity layers 6-3, as shown Figure 3 Compared with one group of polarity change layers, the arrangement of several groups of polarity change layers can induce more hole carriers, thereby further increasing the hole carrier concentration.

[0036] In a specific embodiment, the polarity change of the polarity gradient layer 6-1 from bottom to top is achieved by controlling the Mg doping concentration. The Mg doping concentration of the polarity gradient layer 6-1 is from 1×10 20 cm -3 Gradient to 1×10 21 cm -3 This high Mg doping concentration change mode can make the polarity of the polarity gradient layer 6-1 gradually change from metal polarity to nitrogen polarity. In the metal polarity layer 6-3, the Mg doping concentration is 1×10 18 -1×10 20 cm -3 The lower Mg doping concentration can maintain the metal polarity. The metal atoms of the polarity reversal layer 6-2 can be composed of Al, Ga, Mg, etc., or only Mg.

[0037] In a specific embodiment, in a set of polarity change layers, the thickness of the polarity gradient layer 6-1 is 1-500 nm, and the thickness of the polarity reversal layer 6-2 is 0.1-10 nm. The thinner polarity reversal layer 6-2 is more conducive to the tunneling of hole carriers.

[0038] In a specific embodiment, the Si doping concentration of the n-type electron transport layer 3 is 1×10 18 -1×10 20 cm -3 .

[0039] In a specific embodiment, the Al content in the polarity gradient layer 6-1 can remain constant, or the Al content can vary from high to low from bottom to top. When the Al content varies from high to low from bottom to top, a certain amount of hole carriers can be further polarized and induced based on the hole carriers induced by the metal polarity surface and the nitrogen polarity surface of the polarity gradient layer 6-1, thereby further increasing the hole carrier concentration.

[0040] In a specific embodiment, the thickness of the AlN layer 2 is 100-5000 nm, the thickness of the n-type electron transport layer 3 is 100-5000 nm, the thickness of the electron blocking layer 5 is 1-50 nm, the thickness of the p-type hole transport layer 6, that is, the total thickness of at least one set of polarity change layer and metal polarity layer 6-3 is 10-200 nm, and the thickness of the p-type contact layer 7 is 1-100 nm.

[0041] In a specific embodiment, the Al component content of the electron blocking layer 5 is 0.4-1.0, and the Al component content of the p-type hole transport layer 6 is 0.4-1.0; the multi-quantum well light-emitting layer 4 is formed by alternating growth of barrier layers and well layers, one barrier layer and one well layer constitute one period, the number of periods of the multi-quantum well light-emitting layer 4 is 1-10, the barrier layer thickness is 3-50nm, the Al component content is 0.4-0.7, the well layer thickness is 1-5nm, and the Al component content is 0.3-0.6.

[0042] An embodiment of the present invention further provides a method for preparing an epitaxial structure of an ultraviolet light-emitting device, wherein the epitaxial structure of the ultraviolet light-emitting device is the epitaxial structure of the ultraviolet light-emitting device described in the above embodiment, and the preparation method comprises:

[0043] S1, growing an AlN layer 2 on a substrate 1;

[0044] S2, growing an n-type electron transport layer 3 on the AlN layer 2;

[0045] S3, growing a multi-quantum well light-emitting layer 4 on the n-type electron transport layer 3;

[0046] S4, growing an electron blocking layer 5 on the multi-quantum well light-emitting layer 4;

[0047] S5, growing a p-type hole transport layer 6 on the electron blocking layer 5;

[0048] S6 , growing a p-type contact layer 7 on the p-type hole transport layer 6 .

[0049] Specifically, the growth of the above layers is achieved through MOCVD equipment.

[0050] S1 is specifically implemented as follows: placing the substrate 1 in a MOCVD device, introducing hydrogen into the MOCVD device, controlling the temperature of the MOCVD device to 1200-1500° C. to perform high-temperature cleaning on the substrate 1, and then introducing nitrogen and trimethylaluminum for growth.

[0051] In the specific implementation, S2 includes: controlling the growth temperature of the MOCVD equipment to 900-1300° C., and introducing ammonia, silane, trimethylgallium, trimethylaluminum and hydrogen during the growth.

[0052] In specific implementation, S3 includes: controlling the growth temperature of the MOCVD equipment to 900-1100° C., introducing ammonia, silane, trimethylgallium, trimethylaluminum and hydrogen during growth, and alternately growing barrier layers and well layers.

[0053] In the specific implementation, S4 includes: controlling the growth temperature of the MOCVD equipment to 900-1100° C., and introducing ammonia, silane, trimethylgallium, trimethylaluminum and hydrogen during the growth.

[0054] In specific implementation, S5 includes: growing at least one set of polarity change layers and metal polarity layer 6-3 from bottom to top, and when growing each set of polarity change layers, growing polarity gradient layer 6-1 and polarity reversal layer 6-2 from bottom to top.

[0055] When growing the polarity gradient layer 6-1, the Mg doping concentration is controlled from 1×10 20 cm -3 Gradient to 1×10 21 cm -3 When growing the polarity reversal layer 6-2, the Ga source and Al source can be turned off and only Mg metal atoms can be deposited, so that the polarity changes from nitrogen polarity to metal polarity; when growing the metal polarity layer 6-3, the Mg doping concentration is controlled to be 1×10 18 -1×10 20 cm -3 .

[0056] During the specific growth of S5, pure H2 is used as the carrier gas at a temperature of 900-1100°C and a pressure of 20-100 torr. Ammonia, nitrogen, bismuth magnesium and trimethyl gallium are introduced during the growth, and the V / III molar ratio and the Mg / III molar ratio are controlled to be 100-10000 and 1000-50000.

[0057] In specific implementation, S6 includes: controlling the growth temperature of the MOCVD device to 800-1000° C., and introducing ammonia, nitrogen, bis(cyclopentadienyl)magnesium and trimethylgallium during growth.

[0058] Embodiments of the present invention further provide an ultraviolet light-emitting device comprising the epitaxial structure of the ultraviolet light-emitting device described in the above embodiments. By employing the epitaxial structure of the ultraviolet light-emitting device described above, the ultraviolet light-emitting device in the embodiments of the present invention can increase the hole carrier concentration and longitudinal migration rate, reduce the resistivity of the p-type hole transport layer, and thereby improve the photoelectric conversion efficiency of the ultraviolet light-emitting device.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. An epitaxial structure of an ultraviolet light-emitting device, characterized in that: It comprises a substrate (1), an AlN layer (2), an n-type electron transport layer (3), a multi-quantum well light-emitting layer (4), an electron blocking layer (5), a p-type hole transport layer (6), and a p-type contact layer (7) grown sequentially from bottom to top; The p-type hole transport layer (6) comprises at least one group of polarity change layers and a metal polarity layer (6-3), the polarity change layer comprises a polarity gradient layer (6-1) and a polarity reversal layer (6-2) grown on the polarity gradient layer (6-1), the metal polarity layer (6-3) is grown on the polarity reversal layer (6-2) of the uppermost polarity change layer, the polarity gradient layer (6-1) gradually changes from metal polarity to nitrogen polarity from bottom to top, and the polarity reversal layer (6-2) changes from nitrogen polarity to metal polarity from bottom to top.

2. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: In a set of polarity change layers, the thickness of the polarity gradient layer (6-1) is 1-500 nm, and the thickness of the polarity reversal layer (6-2) is 0.1-10 nm.

3. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: The Si doping concentration of the n-type electron transport layer (3) is 1×10 18 -1×10 20 cm -3 .

4. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: The Al component content in the polarity gradient layer (6-1) remains unchanged, or the Al component content changes from high to low from bottom to top.

5. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: In the polarity gradient layer (6-1), the Mg doping concentration increases from 1×10 20 cm -3 Gradient to 1×10 21 cm -3 ; In the metal polarity layer (6-3), the Mg doping concentration is 1×10 18 -1×10 20 cm -3 .

6. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: The thickness of the AlN layer (2) is 100-5000 nm, the thickness of the n-type electron transport layer (3) is 100-5000 nm, the thickness of the electron blocking layer (5) is 1-50 nm, the thickness of the p-type hole transport layer (6) is 10-200 nm, and the thickness of the p-type contact layer (7) is 1-100 nm.

7. The epitaxial structure of the ultraviolet light emitting device according to claim 1, characterized in that: The Al component content of the electron blocking layer (5) is 0.4-1.0, and the Al component content of the p-type hole transport layer (6) is 0.4-1.0; the period number of the multi-quantum well light-emitting layer (4) is 1-10, the barrier layer thickness is 3-50nm, the Al component content is 0.4-0.7, the well layer thickness is 1-5nm, and the Al component content is 0.3-0.

6.

8. A method for preparing an epitaxial structure of an ultraviolet light-emitting device according to any one of claims 1 to 7, characterized in that: include: S1, growing an AlN layer (2) on a substrate (1); S2, growing an n-type electron transport layer (3) on the AlN layer (2); S3, growing a multi-quantum well light-emitting layer (4) on the n-type electron transport layer (3); S4, growing an electron blocking layer (5) on the multi-quantum well light-emitting layer (4); S5, growing a p-type hole transport layer (6) on the electron blocking layer (5); S6, growing a p-type contact layer (7) on the p-type hole transport layer (6).

9. The preparation method according to claim 8, characterized in that The S5 includes: At least one set of polarity change layers and metal polarity layers (6-3) are grown sequentially from bottom to top, and when each set of polarity change layers is grown, a polarity gradient layer (6-1) and a polarity inversion layer (6-2) are grown sequentially from bottom to top.

10. An ultraviolet light emitting device, characterized in that: The invention comprises the epitaxial structure of the ultraviolet light emitting device according to any one of claims 1 to 7.

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