AlGaN-based deep ultraviolet light-emitting diode epitaxial wafer and preparation method thereof
阅读说明：本技术 AlGaN基深紫外发光二极管的外延片及其制备方法 (AlGaN-based deep ultraviolet light-emitting diode epitaxial wafer and preparation method thereof ) 是由 丁涛 龚程成 尹涌 梅劲 于 2021-06-01 设计创作，主要内容包括：本公开提供了一种AlGaN基深紫外发光二极管的外延片及其制备方法,属于光电子制造技术领域。该外延片包括衬底和依次形成在所述衬底上的AlN层、n型AlGaN层、多量子阱层、p型AlGaN层和p型欧姆接触层；所述p型欧姆接触层包括依次交替层叠的多个p型GaN层和多个六方氮化硼层,沿所述外延片生长的方向,各个所述p型GaN层的掺杂浓度逐层增加。本公开实施例能够提高p型层的导电性能,且缓解AlGaN层和p型GaN层之间的晶格失配的问题,以改善p型层的晶体质量。(The disclosure provides an epitaxial wafer of an AlGaN-based deep ultraviolet light-emitting diode and a preparation method thereof, belonging to the technical field of photoelectron manufacturing. The epitaxial wafer comprises a substrate, and an AlN layer, an n-type AlGaN layer, a multi-quantum well layer, a p-type AlGaN layer and a p-type ohmic contact layer which are sequentially formed on the substrate; the p-type ohmic contact layer comprises a plurality of p-type GaN layers and a plurality of hexagonal boron nitride layers which are sequentially and alternately stacked, and the doping concentration of each p-type GaN layer is increased layer by layer along the growth direction of the epitaxial wafer. According to the embodiment of the disclosure, the conductivity of the p-type layer can be improved, and the problem of lattice mismatch between the AlGaN layer and the p-type GaN layer is relieved, so that the crystal quality of the p-type layer is improved.)
1. The epitaxial wafer of the AlGaN-based deep ultraviolet light-emitting diode is characterized by comprising a substrate (10), and an AlN layer (20), an n-type AlGaN layer (30), a multi-quantum well layer (40), a p-type AlGaN layer (50) and a p-type ohmic contact layer (60) which are sequentially formed on the substrate (10);
the p-type ohmic contact layer (60) comprises a plurality of p-type GaN layers (601) and a plurality of hexagonal boron nitride layers (602) which are sequentially and alternately stacked, and the doping concentration of each p-type GaN layer (601) is increased layer by layer along the growth direction of the epitaxial wafer.
2. The epitaxial wafer according to claim 1, characterized in that the number of layers of the p-type GaN layer (601) is 2 to 5 and the number of layers of the hexagonal boron nitride layer (602) is 2 to 5.
3. The epitaxial wafer according to claim 1, characterized in that the doping concentration of the p-type GaN layer (601) is 1E19/cm-3To 1E20/cm-3。
4. The epitaxial wafer according to claim 3, characterized in that the p-type GaN layer (601) has three layers, the doping concentration of the first layer of the p-type GaN layer (601) is 1E19/cm-3To 3E19/cm-3The doping concentration of the p-type GaN layer (601) of the second layer is 3E19/cm-3To 6E19/cm-3The doping concentration of the p-type GaN layer (601) of the third layer is 6E19/cm-3To 1E20/cm-3。
5. An epitaxial wafer according to any of claims 1 to 4, characterized in that the thickness of each of the p-type GaN layers (601) is the same.
6. The epitaxial wafer according to claim 5, characterized in that the thickness of each p-type GaN layer (601) is 10nm to 100 nm.
7. Epitaxial wafer according to anyone of claims 1 to 4, characterized in that the hexagonal boron nitride layer (602) has two layers, a first layer of the hexagonal boron nitride layer (602) having a thickness comprised between 30nm and 100nm and a second layer of the hexagonal boron nitride layer (602) having a thickness comprised between 15nm and 100 nm.
8. The epitaxial wafer according to claim 7, characterized in that the ratio of the thickness of the hexagonal boron nitride layer (602) of the first layer to the thickness of the hexagonal boron nitride layer (602) of the second layer is comprised between 1.2 and 4.
9. A preparation method of an epitaxial wafer of an AlGaN-based deep ultraviolet light-emitting diode is characterized by comprising the following steps:
providing a substrate;
growing an AlN layer, an n-type AlGaN layer, a multi-quantum well layer, a p-type AlGaN layer and a p-type ohmic contact layer on a substrate at one time, wherein the p-type ohmic contact layer comprises a plurality of p-type GaN layers and a plurality of hexagonal boron nitride layers which are sequentially and alternately stacked, and the doping concentration of each p-type GaN layer is increased layer by layer along the growth direction of the epitaxial wafer.
10. The method according to claim 9, wherein the growth temperature of the p-type GaN layer is 800 ℃ to 1000 ℃, and the growth pressure of the p-type GaN layer is 250mbar to 350 mbar.
Technical Field
The disclosure relates to the technical field of photoelectron manufacturing, in particular to an epitaxial wafer of an AlGaN-based deep ultraviolet light-emitting diode and a preparation method thereof.
Background
The Light Emitting Diode (LED) is a new product with great influence in the photoelectronic industry, has the characteristics of small volume, long service life, rich and colorful colors, low energy consumption and the like, and is widely applied to the fields of illumination, display screens, signal lamps, backlight sources, toys and the like. The core structure of the LED is an epitaxial wafer, and the manufacturing of the epitaxial wafer has great influence on the photoelectric characteristics of the LED.
The epitaxial wafer typically includes an n-type layer, a multiple quantum well layer, and a p-type layer. The AlGaN-based deep ultraviolet light emitting diode is a light emitting diode having a light emitting wavelength of 200nm to 350nm, and a p-type layer in an epitaxial wafer of the AlGaN-based deep ultraviolet light emitting diode generally includes a p-type AlGaN layer.
Because the difficulty of doping in the p-type AlGaN layer is high, in order to improve the carrier concentration of the p-type layer of the AlGaN-based deep ultraviolet light emitting diode and improve the conductivity of the p-type layer, a p-type GaN layer with higher carrier concentration is generally grown on the p-type AlGaN layer, however, the problem of lattice mismatch is easily caused by directly growing the p-type GaN layer on the p-type AlGaN layer, more dislocation defects are generated, the crystal quality of the p-type layer is affected, and thus the conductivity is reduced.
Disclosure of Invention
The embodiment of the disclosure provides an epitaxial wafer of an AlGaN-based deep ultraviolet light-emitting diode and a preparation method thereof, which can improve the conductivity of a p-type layer and relieve the problem of lattice mismatch between the AlGaN layer and a GaN layer so as to improve the crystal quality of the p-type layer. The technical scheme is as follows:
on one hand, the embodiment of the disclosure provides an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode, which comprises a substrate, and an AlN layer, an n-type AlGaN layer, a multi-quantum well layer, a p-type AlGaN layer and a p-type ohmic contact layer which are sequentially formed on the substrate; the p-type ohmic contact layer comprises a plurality of p-type GaN layers and a plurality of hexagonal boron nitride layers which are sequentially and alternately stacked, and the doping concentration of each p-type GaN layer is increased layer by layer along the growth direction of the epitaxial wafer.
Optionally, the number of p-type GaN layers is 2 to 5, and the number of hexagonal boron nitride layers is 2 to 5.
Optionally, doping of the p-type GaN layerThe impurity concentration is 1E19/cm-3To 1E20/cm-3。
Optionally, the p-type GaN layer has three layers, and the doping concentration of the first p-type GaN layer is 1E19/cm-3To 3E19/cm-3The doping concentration of the p-type GaN layer of the second layer is 3E19/cm-3To 6E19/cm-3The doping concentration of the p-type GaN layer of the third layer is 6E19/cm-3To 1E20/cm-3。
Optionally, the thickness of each p-type GaN layer is the same.
Optionally, each of the p-type GaN layers has a thickness of 10nm to 100 nm.
Optionally, the hexagonal boron nitride layer has two layers, a first layer of the hexagonal boron nitride layer has a thickness of 30nm to 100nm, and a second layer of the hexagonal boron nitride layer has a thickness of 15nm to 100 nm.
Optionally, a ratio of a thickness of the hexagonal boron nitride layer of the first layer to a thickness of the hexagonal boron nitride layer of the second layer is 1.2 to 4.
On the other hand, the embodiment of the present disclosure further provides a preparation method of an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode, where the preparation method includes:
providing a substrate; growing an AlN layer, an n-type AlGaN layer, a multi-quantum well layer, a p-type AlGaN layer and a p-type ohmic contact layer on a substrate at one time, wherein the p-type ohmic contact layer comprises a plurality of p-type GaN layers and a plurality of hexagonal boron nitride layers which are sequentially and alternately stacked, and the doping concentration of each p-type GaN layer is increased layer by layer along the growth direction of the epitaxial wafer.
Optionally, the growth temperature of the p-type GaN layer is 800 ℃ to 1000 ℃, and the growth pressure of the p-type GaN layer is 250mbar to 350 mbar.
The beneficial effects brought by the technical scheme provided by the embodiment of the disclosure at least comprise:
the p-type ohmic contact layer can provide holes for compounding, and the hexagonal boron nitride layer has strong conductivity, so that after the hexagonal boron nitride layer is arranged between the p-type GaN layers in an inserting mode, the migration rate of the holes in the whole p-type ohmic contact layer can be increased, namely, the p-type GaN layer is divided into a plurality of film layers with thinner thickness, and the hexagonal boron nitride layer is arranged between the film layers in an inserting mode, so that the hole migration rate of each film layer in the p-type ohmic contact layer is increased one by one, and the hole migration rate of the whole p-type ohmic contact layer is increased. Moreover, the doping concentration of each p-type GaN layer increases layer by layer, that is, as the number of p-type GaN layers increases, the number of hexagonal boron nitride layers inserted between the p-type GaN layers increases, so that the migration rate of holes in the p-type GaN layers is increased, and therefore, the doping concentration of the subsequent p-type GaN layers can be set to be larger without affecting the migration efficiency of the holes in the p-type ohmic contact layer, the migration requirement of a large number of holes is met, and the conductivity of the p-type ohmic contact layer is improved. Therefore, the efficiency of light emission of the combination of holes entering the multiple quantum well layer and electrons can be increased, and the light emitting efficiency of the light emitting diode is improved.
Meanwhile, the structure of the hexagonal boron nitride layer is hexagonal honeycomb, so that the p-type AlGaN layer and the p-type GaN layer can be combined through Van der Waals force, the lattice mismatch between the p-type AlGaN layer and the p-type GaN layer is relieved, and the crystal quality of the p-type GaN layer is improved.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present disclosure, and it is obvious for those skilled in the art to obtain other drawings based on the drawings without creative efforts.
Fig. 1 is a schematic structural diagram of an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 2 is a flowchart illustrating a method for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 3 is a flowchart illustrating a method for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 4 is a schematic view illustrating a process for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 5 is a schematic view illustrating a process for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 6 is a schematic view illustrating a process for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 7 is a schematic view illustrating a process for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure;
fig. 8 is a schematic view of a process for preparing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure.
The individual labels in the figure are illustrated below:
10-a substrate;
20-AlN layer;
a 30-n type AlGaN layer;
40-MQW layer, 401-AlxGa1-xN quantum well layer, 402-AlyGa1-yAn N quantum barrier layer;
a 50-p type AlGaN layer;
60-p type ohmic contact layer, 601-GaN layer, 602-hexagonal boron nitride layer.
Detailed Description
To make the objects, technical solutions and advantages of the present disclosure more apparent, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings.
Fig. 1 is a schematic structural diagram of an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure. As shown in fig. 1, the epitaxial wafer includes a substrate 10, and an AlN layer 20, an n-type AlGaN layer 30, a multiple quantum well layer 40, a p-type AlGaN layer 50, and a p-type ohmic contact layer 60 sequentially formed on the substrate 10.
The P-type ohmic contact layer 60 comprises a plurality of P-type GaN layers 601 and a plurality of hexagonal boron nitride layers 602 which are alternately laminated in sequence, and the doping concentration of each P-type GaN layer 601 increases layer by layer along the growth direction of the epitaxial wafer.
By sequentially forming the AlN layer 20, the n-type AlGaN layer 30, the multiple quantum well layer 40, the p-type AlGaN layer 50, and the p-type ohmic contact layer 60 on the substrate 10, wherein the P-type ohmic contact layer 60 grown on the P-type AlGaN layer 50 includes a plurality of P-type GaN layers 601 and a plurality of hexagonal boron nitride layers 602 alternately stacked in sequence, the P-type GaN layers 601 can provide holes for recombination, the hexagonal boron nitride layer 602 has a relatively strong conductivity, so that the hexagonal boron nitride layer 602 is inserted between the P-type GaN layers 601 to accelerate the migration rate of holes in the entire P-type ohmic contact layer 60, namely, the P-type GaN layer 601 is divided into a plurality of thin film layers, and the hexagonal boron nitride layer 602 is inserted between the film layers, the hole transfer rates of the film layers in the p-type ohmic contact layer 60 are increased one by one, so that the hole transfer rate of the whole p-type ohmic contact layer 60 is increased. Moreover, the doping concentration of each P-type GaN layer 601 increases layer by layer, that is, as the number of the P-type GaN layers 601 increases, the more the number of the hexagonal boron nitride layers 602 inserted between the P-type GaN layers 601 increases, the faster the migration rate of holes in the P-type GaN layers 601 is, so that the doping concentration of the subsequent P-type GaN layer 601 can be set to be larger without affecting the migration efficiency of holes in the P-type ohmic contact layer 60, thereby satisfying the migration requirement of a large number of holes and improving the conductivity of the P-type ohmic layer. Therefore, the efficiency of light emission of the combination of holes entering the multiple quantum well layer 40 and electrons can be increased, and the light emitting efficiency of the light emitting diode is improved.
Meanwhile, the hexagonal boron nitride layer 602 is hexagonal honeycomb-shaped, so that the P-type AlGaN layer 50 and the P-type GaN layer 601 can be combined by van der waals force to relieve lattice mismatch between the P-type AlGaN layer 50 and the P-type GaN layer 601, thereby improving crystal quality of the P-type GaN layer 601.
Alternatively, the substrate 10 is a sapphire substrate 10, a silicon substrate 10, or a silicon carbide substrate 10. The substrate 10 may be a flat sheet substrate 10 or may be a patterned substrate 10.
As an example, in the embodiments of the present disclosure, the substrate 10 is a sapphire substrate 10. The sapphire substrate 10 is a common substrate 10, and has mature technology and low cost. Specifically, the patterned sapphire substrate 10 or the sapphire flat sheet substrate 10 may be used.
Alternatively, the number of P-type GaN layers 601 is 2 to 5, and the number of hexagonal boron nitride layers 602 is 2 to 5.
In the embodiment of the present disclosure, the P-type GaN layer 601 is divided into a plurality of thin film layers, and the hexagonal boron nitride layer 602 is interposed between the film layers, so that the hole mobility rates of the film layers in the P-type ohmic contact layer 60 are increased one by one, and the hole mobility rate of the entire P-type ohmic contact layer 60 is increased. Therefore, in the P-type ohmic contact layer 60, the number of the alternately stacked P-type GaN layers 601 and hexagonal boron nitride layers 602 is too small, the effect of improving the hole transfer rate is not obvious, and the too large number increases the complexity of the manufacturing process and increases the manufacturing cost. The number of the P-type GaN layers 601 and the number of the hexagonal boron nitride layers 602 are set in the thickness range, so that the hole migration rate of the P-type ohmic contact layer 60 is greatly improved, the conductivity of the P-type ohmic contact layer 60 can be improved, and the light emitting efficiency of the light emitting diode can be improved.
As an example, in the embodiment of the present disclosure, the P-type ohmic contact layer 60 includes a 3-layer P-type GaN layer 601 and a 2-layer hexagonal boron nitride layer 602. As shown in fig. 1, the P-type ohmic contact layer 60 includes a first P-type GaN layer 601, a first hexagonal boron nitride layer 602, a second P-type GaN layer 601, a second hexagonal boron nitride layer 602, and a third P-type GaN layer 601 sequentially stacked on the P-type AlGaN layer 50.
Alternatively, the thickness of each P-type GaN layer 601 is the same. The thickness of each P-type GaN layer 601 is set to be the same, and the P-type GaN layers 601 can be formed by the same process during growth, so that when a plurality of P-type GaN layers 601 need to be formed, the growth of each P-type GaN layer 601 can be completed quickly without changing process parameters, and the growth efficiency is improved.
Wherein, the thickness of each P-type GaN layer 601 is 10nm to 100 nm. Since the P-type GaN layer 601 is doped with P-type impurities, the P-type GaN layer 601 is used to provide recombination holes, and the P-type GaN layer 601 needs to have a suitable thickness to cooperate with the hexagonal boron nitride layer 602 to improve the hole mobility and provide more holes. By setting the thickness of the P-type GaN layer 601 in the range of 10nm to 100nm, it is possible to provide a proper amount of holes and improve the hole transfer rate.
As an example, in the embodiments of the present disclosure, the thickness of each P-type GaN layer 601 is 20 nm.
Optionally, the doping concentration of the P-type GaN layer 601 is 1E19/cm-3To 1E20/cm-3. Since the doping concentration of each P-type GaN layer 601 increases layer by layer, that is, as the number of P-type GaN layers 601 increases, the number of hexagonal boron nitride layers 602 interposed between each P-type GaN layer 601 increases, so that the mobility rate of holes in the P-type GaN layer 601 increases. Therefore, the doping concentration of the subsequent P-type GaN layer 601 can be set to be larger without affecting the migration efficiency of holes in the P-type ohmic contact layer 60, thereby meeting the migration requirement of a large number of holes and improving the conductivity of the P-type ohmic layer.
The embodiment of the disclosure sets the doping concentration of the P-type GaN layer 601 at 1E19/cm-3To 1E20/cm-3In this range, the problem that the doping concentration of the P-type GaN layer 601 is too low, which causes the number of holes provided by the P-type GaN layer 601 to be less and affects the light emitting efficiency can be avoided; the problem that the hole transfer rate is affected by too many holes provided by the P-type GaN layer 601 due to too high doping concentration of the P-type GaN layer 601 can also be avoided.
Optionally, the P-type impurity doped in the P-type GaN layer 601 is Mg.
As an example, as shown in FIG. 1, the P-type GaN layer 601 has three layers, and the first P-type GaN layer 601 has a doping concentration of 1E19/cm-3To 3E19/cm-3The doping concentration of the second P-type GaN layer 601 is 3E19/cm-3To 6E19/cm-3The doping concentration of the third P-type GaN layer 601 is 6E19/cm-3To 1E20/cm-3。
Alternatively, as shown in FIG. 1, the hexagonal boron nitride layer 602 has two layers, a first layer of hexagonal boron nitride layer 602 having a thickness of 30nm to 100nm, and a second layer of hexagonal boron nitride layer 602 having a thickness of 15nm to 100 nm.
The thickness of the first hexagonal boron nitride layer 602 is set too thin, which is not obvious for improving the conductivity of the p-type ohmic contact layer 60, and the thickness is set too thick, which increases the manufacturing cost. By setting the thickness of the first hexagonal boron nitride layer 602 in this range, the p-type ohmic contact layer 60 can be improved without increasing the manufacturing cost.
As an example, the thickness of the first hexagonal boron nitride layer 602 is 60 nm.
The thickness of the second hexagonal boron nitride layer 602 is set too thin, which is not obvious for improving the conductivity of the p-type ohmic contact layer 60, and the thickness is set too thick, which increases the manufacturing cost. By setting the thickness of the second hexagonal boron nitride layer 602 in this range, the p-type ohmic contact layer 60 can be improved without increasing the manufacturing cost.
As an example, the thickness of the second hexagonal boron nitride layer 602 is 30 nm.
In the above implementation, the minimum thickness of the first hexagonal boron nitride layer 602 is greater than the minimum thickness of the second hexagonal boron nitride layer 602.
The first hexagonal boron nitride layer 602 can greatly increase the carrier mobility and effectively suppress the dislocation movement, and the second hexagonal boron nitride layer 602 can assist in this case. Thus, the thickness of the first hexagonal boron nitride layer 602 is larger than that of the second hexagonal boron nitride layer 602, the crystal quality of the p-type layer is ensured, and the preparation cost of the p-type layer is reduced.
Optionally, the ratio of the thickness of the first layer of hexagonal boron nitride layer 602 to the thickness of the second layer of hexagonal boron nitride layer 602 is 1.2 to 4. By setting the ratio of the thickness of the first layer hexagonal boron nitride layer 602 to the thickness of the second layer hexagonal boron nitride layer 602 in the above range, the light emission effect of the multiple quantum well layer 40 can be improved to the maximum extent without increasing the manufacturing cost of the p-type layer too much.
As an example, the ratio of the thickness of the first layer of hexagonal boron nitride layer 602 to the thickness of the second layer of hexagonal boron nitride layer 602 is 2. Specifically, the thickness of the first hexagonal boron nitride layer 602 was 60nm, and the thickness of the second hexagonal boron nitride layer 602 was 30 nm.
Optionally, an AlN layer 20 is grown between the substrate 10 and the n-type AlGaN layer 30, and the AlN layer 20 serves as a buffer layer to facilitate carrier transport.
In the disclosed embodiment, the AlN layer 20 may have a thickness of 1 μm to 5 μm. The AlN layer 20 is set to be too thin to serve as a buffer for the AlN layer 20; however, if the AlN layer 20 is set to be too thick, the light absorption of the AlN layer 20 increases.
As an example, in the disclosed embodiment, the thickness of the AlN layer 20 may be 2.5 μm.
In the disclosed embodiment, the thickness of the n-type AlGaN layer 30 is 700 nm.
Optionally, the doping concentration of silane in the n-type AlGaN layer 30 is 1017cm-3To 1018cm-3. Too high a silane doping concentration reduces crystal quality, resulting in increased defects, and too low a silane doping concentration reduces the conductivity of the n-type AlGaN layer 30. Controlling the doping concentration of silane within this range enables the n-type AlGaN layer 30 to have good crystal quality while also having sufficient conductivity.
As an example, in the embodiment of the present disclosure, the doping concentration of silane in the n-type AlGaN layer 30 is 5 × 1017cm-3。
Alternatively, the multiple quantum well layer 40 includes 3 to 8 AlxGa1-xN quantum well layer 401 and AlyGa1-yAnd the N quantum barrier layers 402, wherein x is more than 0 and less than y is less than 1. That is, the multiple quantum well layer 40 includes Al of 3 to 8 periods alternately stackedxGa1-xN quantum well layer 401 and AlyGa1-yN quantum barrier layers 402.
As an example, in the embodiment of the present disclosure, the multiple quantum well layer 40 includes 5 periods of Al alternately stackedxGa1-xN quantum well layer 401 and AlyGa1-yN quantum barrier layers 402.
Alternatively, AlxGa1-xThe thickness of the N quantum well layer 401 may be 2nm to 4 nm. Al (Al)yGa1-yThe thickness of the N quantum barrier layer 402 may be 9 to 14 nm.
Exemplarily, in the embodiments of the present disclosure, AlxGa1-xThe thickness of the N quantum well layer 401 is 3 nm. Al (Al)yGa1-yThe thickness of the N quantum barrier layer 402 is 11 nm.
Note that fig. 1 shows only a partial structure of the multiple quantum well layer 40, and is not intended to limit AlxGa1-xN quantum well layer 401 and AlyGa1-yThe number of cycles of the N quantum barrier layers 402 alternately stacked, and Al may be grown on the N-type AlGaN layer 30 in the case of growing the multiple quantum well layer 40yGa1-yN quantum barrier layers 402.
In the embodiment of the present disclosure, the p-type layer includes a p-type AlGaN layer 50 and a p-type ohmic contact layer 60 sequentially stacked on the multiple quantum well layer 40. The p-type AlGaN layer 50 and the p-type ohmic contact layer 60 are both Mg doped.
Illustratively, the p-type AlGaN layer 50 is a barrier layer.
The p-type AlGaN layer 50 may have a thickness of 5nm to 15 nm. As an example, in the disclosed embodiment, the thickness of the p-type AlGaN layer 50 is 10 nm. If the thickness of the p-type AlGaN layer 50 is too thin, the blocking effect on electrons is reduced, and if the thickness of the p-type AlGaN layer 50 is too thick, the absorption of light by the p-type AlGaN layer 50 increases, and the light emission efficiency of the LED decreases.
Fig. 2 is a flowchart of a method for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode according to an embodiment of the present disclosure. The method is used for preparing the epitaxial wafer shown in fig. 1. As shown in fig. 2, the preparation method comprises:
s11: a substrate 10 is provided.
S12: the AlN layer 20, the n-type AlGaN layer 30, the multiple quantum well layer 40, the p-type AlGaN layer 50, and the p-type ohmic contact layer 60 are grown on the substrate 10 at a time.
The P-type ohmic contact layer 60 comprises a plurality of P-type GaN layers 601 and a plurality of hexagonal boron nitride layers 602 which are alternately laminated in sequence, and the doping concentration of each P-type GaN layer 601 increases layer by layer along the growth direction of the epitaxial wafer.
By sequentially forming the AlN layer 20, the n-type AlGaN layer 30, the multiple quantum well layer 40, the p-type AlGaN layer 50, and the p-type ohmic contact layer 60 on the substrate 10, wherein the P-type ohmic contact layer 60 grown on the P-type AlGaN layer 50 includes a plurality of P-type GaN layers 601 and a plurality of hexagonal boron nitride layers 602 alternately stacked in sequence, the P-type GaN layers 601 can provide holes for recombination, the hexagonal boron nitride layer 602 has a relatively strong conductivity, so that the hexagonal boron nitride layer 602 is inserted between the P-type GaN layers 601 to accelerate the migration rate of holes in the entire P-type ohmic contact layer 60, namely, the P-type GaN layer 601 is divided into a plurality of thin film layers, and the hexagonal boron nitride layer 602 is inserted between the film layers, the hole transfer rates of the film layers in the p-type ohmic contact layer 60 are increased one by one, so that the hole transfer rate of the whole p-type ohmic contact layer 60 is increased. Moreover, the doping concentration of each P-type GaN layer 601 increases layer by layer, that is, as the number of the P-type GaN layers 601 increases, the more the number of the hexagonal boron nitride layers 602 inserted between the P-type GaN layers 601 increases, the faster the migration rate of holes in the P-type GaN layers 601 is, so that the doping concentration of the subsequent P-type GaN layer 601 can be set to be larger without affecting the migration efficiency of holes in the P-type ohmic contact layer 60, thereby satisfying the migration requirement of a large number of holes and improving the conductivity of the P-type ohmic layer. Therefore, the efficiency of light emission of the combination of holes entering the multiple quantum well layer 40 and electrons can be increased, and the light emitting efficiency of the light emitting diode is improved.
Meanwhile, the hexagonal boron nitride layer 602 is hexagonal honeycomb-shaped, so that the P-type AlGaN layer 50 and the P-type GaN layer 601 can be combined by van der waals force to relieve lattice mismatch between the P-type AlGaN layer 50 and the P-type GaN layer 601, thereby improving crystal quality of the P-type GaN layer 601.
Fig. 3 is a flowchart of a method for manufacturing an epitaxial wafer of an AlGaN-based deep ultraviolet light emitting diode, which is used for manufacturing the epitaxial wafer shown in fig. 1. The manufacturing method provided in fig. 3 will be described in detail with reference to fig. 4 to 8:
s21: a substrate 10 is provided.
Alternatively, the substrate 10 is a sapphire substrate 10, a silicon substrate 10, or a silicon carbide substrate 10. The substrate 10 may be a flat sheet substrate 10 or may be a patterned substrate 10.
As an example, in the embodiments of the present disclosure, the substrate 10 is a sapphire substrate 10. The sapphire substrate 10 is a common substrate 10, and has mature technology and low cost. Specifically, the patterned sapphire substrate 10 or the sapphire flat sheet substrate 10 may be used.
In step S21, the sapphire substrate 10 may be pretreated, the sapphire substrate 10 is placed in an MOCVD (Metal-organic Chemical Vapor Deposition) reaction chamber, and the sapphire substrate 10 is subjected to a baking process for 12 to 18 minutes. As an example, in the embodiment of the present disclosure, the sapphire substrate 10 is subjected to the baking process for 15 minutes.
Specifically, the baking temperature can be 1000 ℃ to 1200 ℃, and the pressure in the MOCVD reaction chamber during baking can be 100mbar to 200 mbar.
S22: an AlN layer 20 is epitaxially grown on the substrate 10.
As shown in fig. 4, an AlN layer 20 is grown on the substrate 10. The AlN layer 20 is grown in an MOCVD reactor.
Illustratively, the AlN layer 20 is grown with ammonia gas and trimethylaluminum as reactants, and with a v/iii molar ratio of 100 to 2000, and a process time of 50 to 500s, to form the AlN layer 20.
Alternatively, the growth temperature of the AlN layer 20 is 1000 ℃ to 1500 ℃. The growth temperature affects the growing AlN film, and in this temperature range, an AlN layer 20 of good quality can be grown.
Illustratively, in the disclosed embodiment, the growth temperature of the AlN layer 20 is 1350 ℃, so as to grow the high-temperature AlN layer 20.
In the disclosed embodiment, the AlN layer 20 may have a thickness of 1 μm to 5 μm. The AlN layer 20 is set to be too thin to serve as a buffer for the AlN layer 20; however, if the AlN layer 20 is set to be too thick, the light absorption of the AlN layer 20 increases.
As an example, in the disclosed embodiment, the thickness of the AlN layer 20 may be 2.5 μm.
S23: an n-type AlGaN layer 30 is epitaxially grown on the AlN layer 20.
As shown in fig. 5, an n-type AlGaN layer 30 is grown on the AlN layer 20.
Alternatively, the growth temperature of the n-type AlGaN layer 30 is 1000 ℃ to 1100 ℃. As an example, in the embodiment of the present disclosure, the growth temperature of the n-type AlGaN layer 30 is 1060 ℃.
Alternatively, the growth pressure of the n-type AlGaN layer 30 may be 80mbar to 110 mbar. As an example, in the embodiments of the present disclosure, the growth pressure of the n-type AlGaN layer 30 is 100 mbar.
When the n-type AlGaN layer 30 is grown, silane doping is performed, and the silane doping concentration in the n-type AlGaN layer 30 may be 1017cm-3To 1018cm-3. As an example, in the embodiment of the present disclosure, the Si doping concentration in the n-type AlGaN layer 30 is 5 × 1017cm-3。
The thickness of the n-type AlGaN layer 30 may be 600nm to 800nm, and in the embodiment of the present disclosure, the thickness of the n-type AlGaN layer 30 is 700 nm.
S24: a multiple quantum well layer 40 is grown on the n-type AlGaN layer 30.
As shown in fig. 6, a multiple quantum well layer 40 is grown on the n-type AlGaN layer 30.
In practice, the MQW layer 40 may include a plurality of layers of Al alternately stackedxGa1-xN quantum well layer 401 and multilayer AlyGa1-yAnd the N quantum barrier layers 402, wherein x is more than 0 and less than y is less than 1.
Alternatively, AlxGa1-xN quantum well layer 401 and AlyGa1-yThe number of cycles for which N quantum barrier layers 402 are alternately stacked may be 3 to 8. Exemplarily, in the embodiments of the present disclosure, AlxGa1-xN quantum well layer 401 and AlyGa1-yThe number of cycles of the N quantum barrier layers 402 stacked alternately is 5.
Note that fig. 1 shows only a partial structure of the multiple quantum well layer 40, and is not intended to limit AlxGa1-xN quantum well layer 401 and AlyGa1-yThe number of cycles of the N quantum barrier layers 402 alternately stacked, and Al may be grown on the N-type AlGaN layer 30 in the case of growing the multiple quantum well layer 40yGa1-yN quantum barrier layers 402.
Alternatively, AlxGa1-xThe thickness of the N quantum well layer 401 may be 2nm to 4 nm. Al (Al)yGa1-yThe thickness of the N quantum barrier layer 402 may be 9 to 14 nm.
Exemplarily, in the embodiments of the present disclosure, AlxGa1-xThe thickness of the N quantum well layer 401 is 3nm。AlyGa1-yThe thickness of the N quantum barrier layer 402 is 11 nm.
S25: a p-type AlGaN layer 50 is grown on the multiple quantum well layer 40.
As shown in fig. 7, a p-type AlGaN layer 50 is grown on the multiple quantum well layer 40.
The p-type AlGaN layer 50 is a barrier layer.
Specifically, the growth temperature of the p-type AlGaN layer 50 may be 960 ℃ to 990 ℃, and in the embodiment of the present disclosure, the growth temperature of the p-type AlGaN layer 50 is 980 ℃, as an example.
Specifically, the growth pressure of the p-type AlGaN layer 50 may be 100mbar to 200 mbar. As an example, in the embodiments of the present disclosure, the growth pressure of the p-type AlGaN layer 50 is 150 mbar.
Alternatively, the thickness of the p-type AlGaN layer 50 may be 5nm to 15 nm. As an example, in the disclosed embodiment, the thickness of the p-type AlGaN layer 50 is 10 nm. If the thickness of the p-type AlGaN layer 50 is too thin, the blocking effect on electrons is reduced, and if the thickness of the p-type AlGaN layer 50 is too thick, the absorption of light by the p-type AlGaN layer 50 increases, and the light emission efficiency of the LED decreases.
S26: a p-type ohmic contact layer 60 is grown on the p-type AlGaN layer 50.
As shown in fig. 8, a p-type ohmic contact layer 60 is grown on the p-type AlGaN layer 50.
The P-type ohmic contact layer 60 comprises a plurality of P-type GaN layers 601 and a plurality of hexagonal boron nitride layers 602 which are alternately laminated in sequence, and the doping concentration of each P-type GaN layer 601 increases layer by layer along the growth direction of the epitaxial wafer.
As shown in fig. 8, the P-type ohmic contact layer 60 includes a 3-layer P-type GaN layer 601 and a 2-layer hexagonal boron nitride layer 602. The P-type ohmic contact layer 60 includes a first P-type GaN layer 601, a first hexagonal boron nitride layer 602, a second P-type GaN layer 601, a second hexagonal boron nitride layer 602, and a third P-type GaN layer 601 stacked in this order on the P-type AlGaN layer 50.
Alternatively, the thickness of each P-type GaN layer 601 is the same. Wherein, the thickness of each P-type GaN layer 601 is 10nm to 100 nm. By setting the thickness of the P-type GaN layer 601 in the range of 10nm to 100nm, it is possible to provide a proper amount of holes and improve the hole transfer rate. As an example, in the embodiments of the present disclosure, the thickness of each P-type GaN layer 601 is 20 nm.
Optionally, the doping concentration of the P-type GaN layer 601 is 1E19/cm-3To 1E20/cm-3. Since the doping concentration of each P-type GaN layer 601 increases layer by layer, that is, as the number of P-type GaN layers 601 increases, the number of hexagonal boron nitride layers 602 interposed between each P-type GaN layer 601 increases, so that the mobility rate of holes in the P-type GaN layer 601 increases. Therefore, the doping concentration of the subsequent P-type GaN layer 601 can be set to be larger without affecting the migration efficiency of holes in the P-type ohmic contact layer 60, thereby meeting the migration requirement of a large number of holes and improving the conductivity of the P-type ohmic layer.
Optionally, the P-type impurity doped in the P-type GaN layer 601 is Mg.
As an example, the doping concentration of Mg of the first P-type GaN layer 601 is 1E19/cm-3To 3E19/cm-3The doping concentration of Mg in the second P-type GaN layer 601 is 3E19/cm-3To 6E19/cm-3The Mg doping concentration of the third P-type GaN layer 601 is 6E19/cm-3To 1E20/cm-3。
Alternatively, as shown in FIG. 8, the hexagonal boron nitride layer 602 has two layers, a first hexagonal boron nitride layer 602 having a thickness of 30nm to 100nm, and a second hexagonal boron nitride layer 602 having a thickness of 15nm to 100 nm. As an example, the thickness of the first hexagonal boron nitride layer 602 is 60nm and the thickness of the second hexagonal boron nitride layer 602 is 30 nm.
Optionally, the ratio of the thickness of the first layer of hexagonal boron nitride layer 602 to the thickness of the second layer of hexagonal boron nitride layer 602 is 1.2 to 4.
As an example, the ratio of the thickness of the first layer of hexagonal boron nitride layer 602 to the thickness of the second layer of hexagonal boron nitride layer 602 is 2. Specifically, the thickness of the first hexagonal boron nitride layer 602 was 60nm, and the thickness of the second hexagonal boron nitride layer 602 was 30 nm.
Alternatively, the growth temperature of each P-type GaN layer 601 may be 800 to 1000 ℃. As an example, in the embodiments of the present disclosure, the growth temperature of each P-type GaN layer 601 is 900 ℃.
Alternatively, the growth pressure of each P-type GaN layer 601 may be 250mbar to 350 mbar. As an example, in the embodiments of the present disclosure, the growth pressure of each P-type GaN layer 601 is 300 mbar.
When the P-type AlGaN layer 50 and each P-type GaN layer 601 are grown, Mg doping is performed using cyclopentadienyl magnesium with trimethyl gallium or triethyl gallium as a gallium source.
Alternatively, both hexagonal boron nitride layers 602 are grown by Chemical Vapor Deposition (CVD).
S27: and annealing the epitaxial wafer.
Alternatively, annealing may be performed for 30 minutes in a nitrogen atmosphere to end the growth of the epitaxial wafer. And then the heating system and the gas supply system are closed, and the temperature of the reaction cavity is reduced to room temperature.
In particular implementations, embodiments of the present disclosure may employ high purity H2Or/and N2As carrier gas, TEGa or TMGa is used as Ga source, TMIn is used as In source, SiH4As n-type dopant TMAl as aluminium source, Cp2Mg as a p-type dopant.
The above description is intended to be exemplary only and not to limit the present disclosure, and any modification, equivalent replacement, or improvement made without departing from the spirit and scope of the present disclosure is to be considered as the same as the present disclosure.
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