WO2019015186A1 - 一种紫外led外延结构 - Google Patents

一种紫外led外延结构 Download PDF

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WO2019015186A1
WO2019015186A1 PCT/CN2017/111526 CN2017111526W WO2019015186A1 WO 2019015186 A1 WO2019015186 A1 WO 2019015186A1 CN 2017111526 W CN2017111526 W CN 2017111526W WO 2019015186 A1 WO2019015186 A1 WO 2019015186A1
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layer
ultraviolet led
led epitaxial
epitaxial structure
algan layer
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French (fr)
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何苗
黄波
王成民
周海亮
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广东工业大学
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/04—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction
    • H01L33/06—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a quantum effect structure or superlattice, e.g. tunnel junction within the light emitting region, e.g. quantum confinement structure or tunnel barrier
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/12—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a stress relaxation structure, e.g. buffer layer
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/14—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure
    • H01L33/145—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies with a carrier transport control structure, e.g. highly-doped semiconductor layer or current-blocking structure with a current-blocking structure
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
    • H01L33/00—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
    • H01L33/02—Semiconductor devices having potential barriers specially adapted for light emission; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by the semiconductor bodies
    • H01L33/26—Materials of the light emitting region
    • H01L33/30—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table
    • H01L33/32—Materials of the light emitting region containing only elements of Group III and Group V of the Periodic Table containing nitrogen

Definitions

  • UV LED Ultraviolet (UV) LED is a kind of LED. Compared with traditional gas ultraviolet light sources such as mercury lamps and xenon lamps currently used in the market, ultraviolet LEDs have long life, cold light source, no heat radiation, and the life is not affected by the number of times of opening and closing. High energy, high uniformity of irradiation, and no strong toxic substances make it the most promising replacement of existing UV high pressure mercury lamps, becoming the next generation of UV light source.
  • UV LEDs have significant application value in medical, sterilization, printing, lighting, data storage, and secure communications.
  • 365nm is the most typical wavelength in the UV-A (320nm ⁇ 400nm) wavelength band and has a broad base in UV applications.
  • the preparation and industrialization of high-power 365nm UV LED chips will provide an exemplary role for UV applications. To open up market space for deeper UV, drive the development of LED industry.
  • ultraviolet LEDs are currently in the technological development stage, and there are still some problems that are difficult to break through. For example, the internal quantum efficiency and the transmission power of AlGaN-based ultraviolet LEDs are relatively low.
  • the present invention provides an ultraviolet LED epitaxial structure to solve the problem of low internal quantum efficiency and low transmission power of the ultraviolet LED in the prior art.
  • the present invention provides the following technical solutions:
  • An ultraviolet LED epitaxial structure comprising:
  • the superlattice structure comprises at least one first AlGaN layer and at least one second AlGaN layer, and the first AlGaN layer and the second are alternately stacked.
  • the multiple quantum well structure comprises 6 cycles of Al 0.36 Ga 0.64 N/Al 0.5 Ga 0.5 N grown alternately.
  • the first AlGaN layer is an Al x Ga 1-x N layer
  • the second AlGaN layer is an Al 0.36 Ga 0.64 N layer
  • the first AlGaN layer is grown in the multiple quantum well 0.5 Ga 0.5 N layer surface.
  • the value of x ranges from 0.51 ⁇ x ⁇ 0.57.
  • the superlattice structure comprises 7 cycles of Al x Ga 1-x N/Al 0.36 Ga 0.64 N, each layer of Al x Ga 1-x N layer and each layer of Al 0.36 Ga 0.64 N layer have a thickness It was 1 nm, the doping concentration was 5 ⁇ 10 17 cm -3 , and the growth temperature was 1020 °C.
  • the substrate is a C-plane sapphire substrate.
  • the undoped buffer layer is an Al 0.5 Ga 0.5 N buffer layer having a thickness of 1.5 ⁇ m, a growth temperature of 530 ° C, and the Al 0.5 Ga 0.5 N buffer layer is recrystallized at 1050 ° C for 6 minutes.
  • the N-type AlGaN layer is an N-type Al 0.5 Ga 0.5 N layer having a thickness of 3.0 ⁇ m, a doping concentration of 5 ⁇ 10 18 cm ⁇ 3 , and a growth temperature of 1050° C.
  • the growth temperature in the multiple quantum well is 1020 ° C, wherein each layer of Al 0.36 Ga 0.64 N has a thickness of 8 nm, and each layer of Al 0.5 Ga 0.5 N layer has a thickness of 3 nm.
  • the electron blocking layer is a 10 nm thick P-type Al 0.65 Ga 0.35 N layer having a doping concentration of 2 ⁇ 10 17 cm ⁇ 3 and a growth temperature of 990° C.
  • the P-type AlGaN layer is a 10 nm thick P-type Al 0.5 Ga 0.5 N layer having a doping concentration of 5 ⁇ 10 17 cm ⁇ 3 and a growth temperature of 990° C.
  • the P-type GaN layer has a thickness of 100 nm, a growth temperature of 990 ° C, and a doping concentration of 1 ⁇ 10 18 cm -3 .
  • the ultraviolet LED epitaxial structure provided by the present invention adds a superlattice structure between the multiple quantum well and the electron blocking layer, and the superlattice structure can effectively alleviate the last quantum barrier of the active region.
  • the strain between the electron blocking layers suppresses electron leakage and increases the hole injection rate, thereby improving the light output power and internal quantum efficiency of the ultraviolet LED, so that it exhibits better luminescence performance.
  • by reducing the relationship between the last quantum barrier and the electron blocking layer It significantly reduces the polarization electric field in the quantum well structure of the active region, increases the spatial overlap ratio of the electron and hole wave functions, and weakens the quantum-confined Stark effect, thereby causing electrons and holes in the active region to occur.
  • the probability of radiation recombination increases, which in turn increases the internal quantum efficiency and emission power of the UV LED epitaxial structure.
  • FIG. 1 is a schematic diagram of an epitaxial structure of an ultraviolet LED according to an embodiment of the present invention.
  • FIG. 2 is a schematic structural diagram of a superlattice structure according to an embodiment of the present invention.
  • the internal quantum efficiency and emission power of the prior art AlGaN-based ultraviolet LEDs are relatively low.
  • AlGaN-based UV LED light source the reasons for the low luminous efficiency of AlGaN-based UV LED light source are as follows: high Al-component AlGaN material has low carrier injection efficiency, which restricts the increase of quantum efficiency in UV LED; the structural properties of high-Al composition AlGaN material determine its light output. low efficiency.
  • an ultraviolet LED epitaxial structure which comprises:
  • the superlattice structure comprises at least one first AlGaN layer and at least one second AlGaN layer, and the first AlGaN layer and the second are alternately stacked.
  • the ultraviolet LED epitaxial structure provided by the invention increases a superlattice structure between the multiple quantum well and the electron blocking layer, and the superlattice structure can effectively alleviate the last quantum barrier between the active region and the electron blocking layer. Strain, suppress electron leakage, increase hole injection rate, and thus increase purple The external LED's optical output power and internal quantum efficiency make it exhibit better luminescence performance.
  • the polarization electric field in the quantum well structure of the active region is significantly weakened, and the spatial overlap ratio of the electron and hole wave functions is increased, and the quantum is weakened.
  • the Stark effect is limited, so that the probability of radiation recombination of electrons and holes in the active region is increased, thereby improving the internal quantum efficiency and the emission power of the epitaxial structure of the ultraviolet LED.
  • an ultraviolet LED epitaxial structure comprising: a substrate 1; an undoped buffer layer 2, an N-type AlGaN layer 3, and a multiple quantum well structure sequentially grown on the substrate 1. 4, a superlattice structure 5, an electron blocking layer 6, a P-type AlGaN layer 7 and a P-type GaN layer 8; wherein the superlattice structure 5 comprises at least one first AlGaN layer and at least one second AlGaN layer, An AlGaN layer and a second alternating stack.
  • the specific structure of the superlattice structure 5 is not limited.
  • the superlattice structure 5 includes at least one first AlGaN layer, Al x Ga 1 . -x N layer a and at least one second AlGaN layer - Al 0.36 Ga 0.64 N layer b, Al x Ga 1-x N layer a and Al 0.36 Ga 0.64 N layer b are alternately stacked, wherein the first AlGaN layer - —Al x Ga 1-x N layer a is grown on the surface of the multiple quantum well.
  • the period of the overlapping structure of the first AlGaN layer and the second AlGaN layer in the superlattice structure is not limited in the embodiment of the present invention.
  • 7 cycles of Al x Ga 1-x N/Al are included in this embodiment. 0.36 Ga 0.64 N.
  • the value range of x in the Al x Ga 1-x N layer is not limited.
  • the inventor obtains a simulation when the value range of x is 0.51 ⁇ x ⁇ 0.57, and the superlattice structure is obtained.
  • the thickness of each layer structure is the same, both are 1 nm, the doping concentration is 5 ⁇ 10 17 cm -3 , and the growth temperature is 1020 ° C, which makes the internal quantum efficiency and output power of the UV LED epitaxial structure more obvious.
  • the undoped buffer layer is Al 0.5 Ga 0.5 N buffer.
  • the layer had a thickness of 1.5 ⁇ m, a growth temperature of 530 ° C, and the Al 0.5 Ga 0.5 N buffer layer was recrystallized at 1050 ° C for 6 minutes.
  • the N-type AlGaN layer is an N-type Al 0.5 Ga 0.5 N layer having a thickness of 3.0 ⁇ m, a doping concentration of 5 ⁇ 10 18 cm -3 , and a growth temperature of 1,050 °C.
  • the growth temperature in the multiple quantum well was 1020 ° C, wherein each layer of Al 0.36 Ga 0.64 N had a thickness of 8 nm, and each layer of Al 0.5 Ga 0.5 N layer had a thickness of 3 nm.
  • the structure of the multiple quantum well in this embodiment includes 6 cycles of Al 0.36 Ga 0.64 N/Al 0.5 Ga 0.5 N alternately grown. In other embodiments, the period of the multiple quantum well structure may also be other values, which is not limited in this embodiment.
  • the electron blocking layer was a 10 nm thick P-type Al 0.65 Ga 0.35 N layer having a doping concentration of 2 ⁇ 10 17 cm -3 and a growth temperature of 990 ° C.
  • the P-type AlGaN layer was a 10 nm thick P-type Al 0.5 Ga 0.5 N layer having a doping concentration of 5 ⁇ 10 17 cm -3 and a growth temperature of 990 ° C.
  • the P-type GaN layer has a thickness of 100 nm, a growth temperature of 990 ° C, and a doping concentration of 1 ⁇ 10 18 cm -3 .
  • different x values may be set according to different material compositions of different structural layers, so that the internal quantum efficiency and output power of the ultraviolet LED epitaxial structure are significantly improved.
  • the substrate is sapphire.
  • the sapphire is often used in the facets of the A side, the C side, and the R side.
  • the lattice constant ratio between the C-plane of sapphire and the deposited films of Group III-V and II-VI is small, and meets the requirements of high temperature resistance in the GaN barrier process. Therefore, in this embodiment, the The substrate is a C-plane sapphire substrate.
  • the ultraviolet LED epitaxial structure provided by the invention increases a superlattice structure between the multiple quantum well and the electron blocking layer, and the superlattice structure can effectively alleviate the last quantum barrier between the active region and the electron blocking layer. Strain, suppress electron leakage, increase hole injection rate, thereby improving the light output power and internal quantum efficiency of the ultraviolet LED, so that it exhibits better luminescence performance.
  • the polarization electric field in the quantum well structure of the active region is significantly weakened, and the spatial overlap ratio of the electron and hole wave functions is increased, and the quantum is weakened. Limiting the Stark effect, causing the electrons and holes in the active region to recombine with radiation The increase, thereby increasing the internal quantum efficiency and the emission power of the ultraviolet LED epitaxial structure.
  • each layer structure can be fabricated by MOCVD (Metal-organic Chemical Vapor DePosition) equipment.
  • MOCVD Metal-organic Chemical Vapor DePosition
  • the embodiment of the present invention further provides a method for fabricating the ultraviolet LED epitaxial structure, including:
  • a sapphire substrate is placed in the reaction chamber.
  • the substrate was fired at a high temperature of 1090 ° C with high purity hydrogen.
  • a low-temperature undoped Al 0.5 Ga 0.5 N buffer layer was grown through a Ga source, an Al source, and a nitrogen source at 530 ° C.
  • the thickness of the undoped Al 0.5 Ga 0.5 N buffer layer was about 1.5 ⁇ m.
  • the temperature was raised to 1050 ° C and kept at a constant temperature for about 6 minutes, so that the undoped Al 0.5 Ga 0.5 N buffer layer was recrystallized.
  • a Ga source, an Al source, ammonia gas, and silane SiH 4 were introduced at 1050 ° C to grow an N-type Al 0.5 Ga 0.5 N layer having a doping concentration of 5 ⁇ 10 18 cm -3 and a thickness of 3 ⁇ m.
  • the temperature was lowered to 1020 ° C and a Ga source, an Al source, and a nitrogen source were passed to grow an 8 nm thick Al 0.36 Ga 0.64 N quantum barrier.
  • a 3 nm thick Al 0.5 Ga 0.5 N quantum well was grown at 1020 °C. The first two steps were repeated to grow a total of 6 cycles of Al 0.36 Ga 0.64 N/Al 0.5 Ga 0.5 N multiple quantum well structure.
  • the temperature was lowered to 990 ° C, and an Al source, a Ga source, an ammonia gas, and a Mg source were introduced to grow an Al x Ga 1-x N/Al 0.36 Ga 0.64 N superlattice structure.
  • x has a value in the range of 0.51 ⁇ x ⁇ 0.57.
  • the superlattice structure was alternately grown for 7 cycles of Al x Ga 1-x N/Al 0.36 Ga 0.64 N , and the thickness of each layer of AlGaN was 1 nm, and the doping concentration was 5 ⁇ 10 17 cm -3 .
  • a 100 nm thick P-type GaN layer was grown at 990 ° C with a doping concentration of 1 ⁇ 10 18 cm -3 and annealed at 700 ° C for 20 minutes to obtain a P-type GaN layer having a high hole concentration.
  • the specific form of the Ga source and the Al source is not limited.
  • the Ga source used in the embodiment is trimethylgallium TMGa
  • the Al source is trimethylaluminumTMAl, nitrogen.
  • the source is ammonia gas NH 3
  • the carrier gas is H 2
  • the N-type and P-type dopant sources are silane SiH 4 and ferrocene Cp 2 Mg, respectively.
  • the AlGaN superlattice structure is adopted by the above-mentioned ultraviolet LED epitaxial structure, which can reduce the polarization effect, weaken the energy band bending between the electron blocking layer EBL and the P-type AlGaN layer, and the red shift phenomenon is improved, and the shorter emission wavelength is exhibited.
  • the luminous intensity also increases; the output power can be greatly improved, and the output power increases with the increase of current, showing better power performance; reducing the difficulty of recombination of electrons and holes, thus requiring The energy is reduced, so that it has a smaller turn-on voltage; due to the design of the new structure, the voltage change of the chip with the increase of current is small, showing better diode performance; moreover, P-type doping can be realized more effectively. Enhancing the conductivity, causing the resistance to decrease, thereby reducing the operating voltage, which is beneficial to reducing the energy consumption of the ultraviolet LED chip and saving energy.

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Abstract

一种紫外LED外延结构，包括：衬底（1）；依次生长在所述衬底（1）上的未掺杂缓冲层（2）、N型AlGaN层（3）、多量子阱结构（4）、超晶格结构（5）、电子阻挡层（6）、P型AlGaN层（7）和P型GaN层（8）；其中，所述超晶格结构（5）包括至少一层第一AlGaN层和至少一层第二AlGaN层，所述第一AlGaN层和所述第二交替叠加。由于在多量子阱与电子阻挡层（6）之间增加设置超晶格结构（5），超晶格结构（5）能够有效缓解有源区最后一个量子垒与电子阻挡层（6）之间的应变，抑制电子泄漏，增大空穴注入率，从而提高紫外LED的光输出功率和内量子效率，使其呈现更佳的发光性能。

Description

一种紫外LED外延结构 技术领域
本申请要求于2017年7月21日提交中国专利局、申请号为201710600473.9、发明名称为“一种紫外LED外延结构”的国内申请的优先权，其全部内容通过引用结合在本申请中。
背景技术
紫外(UV)LED是LED的一种，与目前市面上使用的汞灯和氙灯等传统气体紫外光源相比，紫外LED具备超长寿命、冷光源、无热辐射、寿命不受开闭次数影响、能量高、照射均匀效率高，不含有毒物质等强大优势，使其最有希望取代现有的紫外高压水银灯，成为下一代的紫外光光源。
紫外LED在医疗、杀菌、印刷、照明、数据存储以及保密通信等方面都有重大应用价值。365nm作为紫外UV-A(320nm～400nm)波段最典型的波长，在紫外应用上有广泛的基础。而通过大功率365nm紫外LED芯片的制备与产业化实现，将会对紫外产品应用提供示范作用。为更深波段的紫外开拓市场空间，带动LED产业发展。
但目前紫外LED正处于技术发展期，还存在一些难以突破的问题，如AlGaN基紫外LED的内量子效率和发射功率相对较低。
因此，如何提高AlGaN基紫外LED的内量子效率和发射功率成为亟待解决的问题。
发明内容
有鉴于此，本发明提供一种紫外LED外延结构，以解决现有技术中紫外LED的内量子效率和发射功率较低的问题。
为实现上述目的，本发明提供如下技术方案：
一种紫外LED外延结构，包括：
衬底；
依次生长在所述衬底上的未掺杂缓冲层、N型AlGaN层、多量子阱结构、超晶格结构、电子阻挡层、P型AlGaN层和P型GaN层；
其中，所述超晶格结构包括至少一层第一AlGaN层和至少一层第二AlGaN层，所述第一AlGaN层和所述第二交替叠加。
优选地，所述多量子阱结构包括交替生长的6个周期的Al0.36Ga0.64N/Al0.5Ga0.5N。
优选地，所述第一AlGaN层为AlxGa1-xN层，所述第二AlGaN层为Al0.36Ga0.64N层，且所述第一AlGaN层生长在所述多量子阱中的Al0.5Ga0.5N层表面。
优选地，所述x的取值范围为0.51≤x≤0.57。
优选地，所述超晶格结构包括7个周期的AlxGa1-xN/Al0.36Ga0.64N，每层AlxGa1-xN层和每层Al0.36Ga0.64N层的厚度均为1nm，掺杂浓度为5×1017cm-3，生长温度为1020℃。
优选地，所述衬底为C面的蓝宝石衬底。
优选地，所述未掺杂缓冲层为Al0.5Ga0.5N缓冲层，厚度为1.5μm，生长温度为530℃，且所述Al0.5Ga0.5N缓冲层在1050℃恒温6分钟重结晶。
优选地，所述N型AlGaN层为N型Al0.5Ga0.5N层，厚度为3.0μm，掺杂浓度为5×1018cm-3，生长温度为1050℃。
优选地，所述多量子阱中的生长温度为1020℃，其中，每层Al0.36Ga0.64N厚度为8nm，每层Al0.5Ga0.5N层厚度为3nm。
优选地，所述电子阻挡层为10nm厚的P型Al0.65Ga0.35N层，掺杂浓度为2×1017cm-3，生长温度为990℃。
优选地，所述P型AlGaN层为10nm厚的P型Al0.5Ga0.5N层，掺杂浓度为5×1017cm-3，生长温度为990℃。
优选地，所述P型GaN层，厚度为100nm，生长温度为990℃，掺杂浓度为1×1018cm-3。
经由上述的技术方案可知，本发明提供的紫外LED外延结构，在多量子阱与电子阻挡层之间增加设置超晶格结构，所述超晶格结构能够有效缓解有源区最后一个量子垒与电子阻挡层之间的应变，抑制电子泄漏，增大空穴注入率，从而提高紫外LED的光输出功率和内量子效率，使其呈现更佳的发光性能。另外，通过降低最后一个量子垒和电子阻挡层之间打的应 变来显著减弱有源区量子阱结构中的极化电场，并增加电子和空穴波函数在空间上的重叠率，减弱了量子限制斯塔克效应，从而使得有源区电子和空穴发生辐射复合的几率增大，进而提高了紫外LED外延结构的内量子效率和发射功率。
附图说明
为了更清楚地说明本发明实施例或现有技术中的技术方案，下面将对实施例或现有技术描述中所需要使用的附图作简单地介绍，显而易见地，下面描述中的附图仅仅是本发明的实施例，对于本领域普通技术人员来讲，在不付出创造性劳动的前提下，还可以根据提供的附图获得其他的附图。
图1为本发明实施例提供的一种紫外LED外延结构示意图；
图2为本发明实施例提供的一种超晶格结构的结构示意图。
具体实施方式
正如背景技术部分所述，现有技术中AlGaN基紫外LED的内量子效率和发射功率相对较低。
目前AlGaN基紫外LED光源发光效率低的原因主要有：高Al组分AlGaN材料的载流子注入效率低，制约了紫外LED内量子效率的提高；高Al组分AlGaN材料的结构性质决定其出光效率低。
基于此，本发明提供一种紫外LED外延结构，其特征在于，包括：
衬底；
依次生长在所述衬底上的未掺杂缓冲层、N型AlGaN层、多量子阱结构、超晶格结构、电子阻挡层、P型AlGaN层和P型GaN层；
其中，所述超晶格结构包括至少一层第一AlGaN层和至少一层第二AlGaN层，所述第一AlGaN层和所述第二交替叠加。
本发明提供的紫外LED外延结构，在多量子阱与电子阻挡才层之间增加设置超晶格结构，所述超晶格结构能够有效缓解有源区最后一个量子垒与电子阻挡层之间的应变，抑制电子泄漏，增大空穴注入率，从而提高紫 外LED的光输出功率和内量子效率，使其呈现更佳的发光性能。另外，通过降低最后一个量子垒和电子阻挡层之间打的应变来显著减弱有源区量子阱结构中的极化电场，并增加电子和空穴波函数在空间上的重叠率，减弱了量子限制斯塔克效应，从而使得有源区电子和空穴发生辐射复合的几率增大，进而提高了紫外LED外延结构的内量子效率和发射功率。
下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行清楚、完整地描述，显然，所描述的实施例仅仅是本发明一部分实施例，而不是全部的实施例。基于本发明中的实施例，本领域普通技术人员在没有做出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。
请参见图1，为本发明实施例提供的一种紫外LED外延结构，包括：衬底1；依次生长在衬底1上的未掺杂缓冲层2、N型AlGaN层3、多量子阱结构4、超晶格结构5、电子阻挡层6、P型AlGaN层7和P型GaN层8；其中，超晶格结构5包括至少一层第一AlGaN层和至少一层第二AlGaN层，第一AlGaN层和第二交替叠加。
需要说明的是，本发明实施例中不限定超晶格结构5的具体结构，可选的，如图2所示，超晶格结构5包括至少一层第一AlGaN层——AlxGa1-xN层a和至少一层第二AlGaN层——Al0.36Ga0.64N层b，AlxGa1-xN层a和Al0.36Ga0.64N层b交替叠加，其中，第一AlGaN层——AlxGa1-xN层a生长在所述多量子阱的表面。
本发明实施例中不限定超晶格结构中第一AlGaN层和第二AlGaN层的交叠结构的周期，可选的，本实施例中包括7个周期的AlxGa1-xN/Al0.36Ga0.64N。本发明实施例中不限定AlxGa1-xN层中x的取值范围，可选的，发明人经过模拟得到当x的取值范围为0.51≤x≤0.57时，且超晶格结构中每层结构的厚度为相同，均为1nm，掺杂浓度为5×1017cm-3，生长温度为1020℃，从而使得紫外LED外延结构的内量子效率和输出功率提高较为明显。
需要说明的是，在本发明中不限定未掺杂缓冲层、N型AlGaN层、多量子阱结构、电子阻挡层、P型AlGaN层和P型GaN层中各种物质的组分。为了在x的取值范围为0.51≤x≤0.57时，紫外LED外延结构的内量子效率和输出功率提高较为明显，本实施例中可选的，未掺杂缓冲层为Al0.5Ga0.5N缓冲层，厚度为1.5μm，生长温度为530℃，且所述Al0.5Ga0.5N缓冲层在1050℃恒温6分钟重结晶。N型AlGaN层为N型Al0.5Ga0.5N层，厚度为3.0μm，掺杂浓度为5×1018cm-3，生长温度为1050℃。多量子阱中的生长温度为1020℃，其中，每层Al0.36Ga0.64N厚度为8nm，每层Al0.5Ga0.5N层厚度为3nm。本实施例中多量子阱的结构包括交替生长的6个周期的Al0.36Ga0.64N/Al0.5Ga0.5N。在其他实施例中，多量子阱结构的周期还可以为其他数值，本实施例中对此不做限定。电子阻挡层为10nm厚的P型Al0.65Ga0.35N层，掺杂浓度为2×1017cm-3，生长温度为990℃。P型AlGaN层为10nm厚的P型Al0.5Ga0.5N层，掺杂浓度为5×1017cm-3，生长温度为990℃。P型GaN层，厚度为100nm，生长温度为990℃，掺杂浓度为1×1018cm-3。在本发明的其他实施例中，可以根据不同的结构层的材质组分不同，而设置不同x值，以使得紫外LED外延结构的内量子效率和输出功率提高较为明显。
本实施例中不限定衬底的具体材质，可以根据实际需求进行选择，需要说明的是，由于蓝宝石具有较高的透光性，本实施例中可选的，所述衬底为蓝宝石。蓝宝石常被运用的切面有A面、C面、R面。蓝宝石的C面与III-V族和II-VI族沉积薄膜之间的晶格常数适配率小，同时符合GaN垒晶制程中耐高温的要求，因此，本实施例中可选的，所述衬底为C面的蓝宝石衬底。
本发明提供的紫外LED外延结构，在多量子阱与电子阻挡才层之间增加设置超晶格结构，所述超晶格结构能够有效缓解有源区最后一个量子垒与电子阻挡层之间的应变，抑制电子泄漏，增大空穴注入率，从而提高紫外LED的光输出功率和内量子效率，使其呈现更佳的发光性能。另外，通过降低最后一个量子垒和电子阻挡层之间打的应变来显著减弱有源区量子阱结构中的极化电场，并增加电子和空穴波函数在空间上的重叠率，减弱了量子限制斯塔克效应，从而使得有源区电子和空穴发生辐射复合的几率 增大，进而提高了紫外LED外延结构的内量子效率和发射功率。
对于上述提供的深紫外LED结构，本发明不限定紫外LED外延结构的制作方法，可选的，可以采用MOCVD(Metal-organic Chemical Vapor DePosition，金属有机化合物化学气相淀积)设备制作各层结构。具体地，本发明实施例还提供一种制作所述紫外LED外延结构的制作方法，包括：
首先，将蓝宝石衬底置入反应室。
然后，在1090℃通高纯氢气高温灼烧衬底。
接着，在530℃下通Ga源、Al源和氮源生长低温未掺杂的Al0.5Ga0.5N缓冲层，未掺杂的Al0.5Ga0.5N缓冲层的厚度约为1.5μm。然后，升温到1050℃并恒温6分钟左右，使得未掺杂的Al0.5Ga0.5N缓冲层重结晶。
随后，在1050℃下通入Ga源、Al源、氨气和硅烷SiH4，生长N型Al0.5Ga0.5N层，其掺杂浓度为5×1018cm-3，厚度为3μm。
接下来，降温到1020℃并通入Ga源、Al源、氮源生长8nm厚的Al0.36Ga0.64N量子垒。接着，在1020℃生长3nm厚的Al0.5Ga0.5N量子阱。重复前两步步骤，共生长6个周期的Al0.36Ga0.64N/Al0.5Ga0.5N多量子阱结构。
紧接着，降温到990℃，通入Al源，Ga源，氨气和Mg源，生长AlxGa1-xN/Al0.36Ga0.64N超晶格结构。AlxGa1-xN/Al0.36Ga0.64N超晶格结构中，其x的取值范围为0.51≤x≤0.57。超晶格结构为AlxGa1-xN/Al0.36Ga0.64N两者交替生长7个周期，每层AlGaN的厚度是1nm，掺杂浓度为5×1017cm-3。
然后，在990℃下，在超晶格结构之上生长一层10nm厚的P型 Al0.65Ga0.35N电子阻挡层，其掺杂浓度为2×1017cm-3。
接着，在990℃下，生长一层10nm厚的P型Al0.5Ga0.5N层，掺杂浓度为5×1017cm-3。
最后，在990℃下，生长一层100nm厚的P型GaN层，掺杂浓度为1×1018cm-3，并在700℃退火20分钟，得到高空穴浓度的P型GaN层。
需要说明的是，本实施例中不限定Ga源、Al源的具体形式，可选的，本实施例中所采用的Ga源为三甲基镓TMGa，Al源为三甲基铝TMAl，氮源为氨气NH3，载气为H2，N型和P型掺杂源分别为硅烷SiH4和二茂镁Cp2Mg。
由上述紫外LED外延结构采用了AlGaN超晶格结构，能减少极化效应，削弱电子阻挡层EBL到P型AlGaN层之间的能带弯曲，使得红移现象得到改善，呈现更短的发光波长，发光强度也随之增大；输出功率能得到大幅度提升，且输出功率随电流的增幅增大，呈现较好的功率性能；降低了电子和空穴复合的难易程度，因而所需的能量下降，使得具有更小的开启电压；由于新结构的设计，可使得芯片随电流的增加其电压改变较小，显示出更好的二极管性能；再者，能更有效实现P型掺杂，增强导电性，促使电阻降低，从而减小工作电压，这有利于减少紫外LED芯片的能耗，节约能源。
需要说明的是，本说明书中的各个实施例均采用递进的方式描述，每个实施例重点说明的都是与其他实施例的不同之处，各个实施例之间相同相似的部分互相参见即可。
对所公开的实施例的上述说明，使本领域专业技术人员能够实现或使用本发明。对这些实施例的多种修改对本领域的专业技术人员来说将是显而易见的，本文中所定义的一般原理可以在不脱离本发明的精神或范围的情况下，在其它实施例中实现。因此，本发明将不会被限制于本文所示的这些实施例，而是要符合与本文所公开的原理和新颖特点相一致的最宽的范围。

Claims (12)

  1. 一种紫外LED外延结构，其特征在于，包括：
    衬底；
    依次生长在所述衬底上的未掺杂缓冲层、N型AlGaN层、多量子阱结构、超晶格结构、电子阻挡层、P型AlGaN层和P型GaN层；
    其中，所述超晶格结构包括至少一层第一AlGaN层和至少一层第二AlGaN层，所述第一AlGaN层和所述第二交替叠加。
  2. 根据权利要求1所述的紫外LED外延结构，其特征在于，所述多量子阱结构包括交替生长的6个周期的Al0.36Ga0.64N/Al0.5Ga0.5N。
  3. 根据权利要求2所述的紫外LED外延结构，其特征在于，所述第一AlGaN层为AlxGa1-xN层，所述第二AlGaN层为Al0.36Ga0.64N层，且所述第一AlGaN层生长在所述多量子阱中的Al0.5Ga0.5N层表面。
  4. 根据权利要求3所述的紫外LED外延结构，其特征在于，所述x的取值范围为0.51≤x≤0.57。
  5. 根据权利要求4所述的紫外LED外延结构，其特征在于，所述超晶格结构包括7个周期的AlxGa1-xN/Al0.36Ga0.64N，每层AlxGa1-xN层和每层Al0.36Ga0.64N层的厚度均为1nm，掺杂浓度为5×1017cm-3，生长温度为1020℃。
  6. 根据权利要求1-5任意一项所述的紫外LED外延结构，其特征在于，所述衬底为C面的蓝宝石衬底。
  7. 根据权利要求1-5任意一项所述的紫外LED外延结构，其特征在于，所述未掺杂缓冲层为Al0.5Ga0.5N缓冲层，厚度为1.5μm，生长温度为530℃，且所述Al0.5Ga0.5N缓冲层在1050℃恒温6分钟重结晶。
  8. 根据权利要求1-5任意一项所述的紫外LED外延结构，其特征在于，所述N型AlGaN层为N型Al0.5Ga0.5N层，厚度为3.0μm，掺杂浓度为5×1018cm-3，生长温度为1050℃。
  9. 根据权利要求2所述的紫外LED外延结构，其特征在于，所述多量子阱中的生长温度为1020℃，其中，每层Al0.36Ga0.64N厚度为8nm，每层Al0.5Ga0.5N层厚度为3nm。
  10. 根据权利要求1所述的紫外LED外延结构，其特征在于，所述电子阻挡层为10nm厚的P型Al0.65Ga0.35N层，掺杂浓度为2×1017cm-3，生长温度为990℃。
  11. 根据权利要求1所述的紫外LED外延结构，其特征在于，所述P型AlGaN层为10nm厚的P型Al0.5Ga0.5N层，掺杂浓度为5×1017cm-3，生长温度为990℃。
  12. 根据权利要求1所述的紫外LED外延结构，其特征在于，所述P型GaN层，厚度为100nm，生长温度为990℃，掺杂浓度为1×1018cm-3。
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