CN117637943A - Ultraviolet LED epitaxial wafer, preparation method thereof and LED chip - Google Patents

Abstract

The invention provides an ultraviolet LED epitaxial wafer and a preparation method thereof, and an LED chip, wherein the ultraviolet LED epitaxial wafer is provided with a nucleation layer, the nucleation layer comprises a first nucleation layer and a second nucleation layer which are sequentially laminated, the first nucleation layer and the second nucleation layer are all AlN layers, wherein the temperature and the speed for growing the first nucleation layer are lower than those for growing the second nucleation layer, the pressure for growing the first nucleation layer, the Gap height are higher than those for growing the second nucleation layer, and NH is introduced when the first nucleation layer is grown ₃ Is greater than NH introduced during growth of the second nucleation layer ₃ After the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the impurity crystal and the polycrystalline substance to obtain a nucleation layer with clear surface morphology, wherein the nucleation layer can be arranged as a growth pad foundation of a subsequent buffer layerThe buffer layer with better crystal quality is conveniently obtained, and finally the aim of improving the internal quantum efficiency is fulfilled.

Description

Ultraviolet LED epitaxial wafer, preparation method thereof and LED chip

Technical Field

The invention relates to the technical field of semiconductors, in particular to an ultraviolet LED epitaxial wafer, a preparation method thereof and an LED chip.

Background

Ultraviolet LEDs (UV LEDs) are mainly used in biomedical, anti-counterfeit, purification (water, air, etc.), computer data storage, military, etc.

The development of ultraviolet LEDs has faced a number of unique technical difficulties compared to GaN-based blue LEDs, such as: epitaxial growth of high Al composition AlGaN material is difficult, and in general, the higher the Al composition is, the lower the crystal quality is, and the dislocation density is generally 10 ⁹ ～10 ¹⁰ /cm ² Or even higher; the doping of AlGaN materials is much more difficult than GaN, both n-type and p-type doping, and as the Al composition increases, the conductivity of the epitaxial layer decreases rapidly, especially p-AlGaN doping is particularly troublesome, the activation efficiency of the dopant Mg is low, resulting in insufficient holes, sharp decreases in conductivity and luminous efficiency, and so on.

Due to the above-mentioned situation, the internal quantum efficiency of the existing uv LED epitaxial wafer is not high, and in the prior art, in order to improve the internal quantum efficiency of the uv LED epitaxial wafer, a method is generally adopted to reduce the Al component of the electron blocking layer and improve the doping concentration of Mg, thereby improving the hole concentration, but in this way, the electron overflow phenomenon is aggravated, and the aging performance is also worsened.

Disclosure of Invention

Based on the above, the invention aims to provide an ultraviolet LED epitaxial wafer, a preparation method thereof and an LED chip, and aims to introduce a novel nucleation layer structure into the ultraviolet LED epitaxial wafer so as to improve internal quantum efficiency.

According to the embodiment of the invention, the ultraviolet LED epitaxial wafer comprises a nucleation layer, wherein the nucleation layer comprises a first nucleation layer and a second nucleation layer which are sequentially laminated, the first nucleation layer and the second nucleation layer are AlN layers, the temperature for growing the first nucleation layer is lower than that for growing the second nucleation layer, and the speed for growing the first nucleation layer is lower than that for growing the second nucleation layerThe pressure for growing the first nucleation layer is higher than the pressure for growing the second nucleation layer, the Gap height of the first nucleation layer is higher than the Gap height of the second nucleation layer, the difference between the Gap height when the first nucleation layer is grown and the Gap height when the second nucleation layer is grown is 5-9 mm, and NH is introduced when the first nucleation layer is grown ₃ Is greater than NH is introduced during growth of the second nucleation layer ₃ And (3) after the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the substances with mixed crystals and multiple crystals, thereby obtaining the nucleation layer with clear surface morphology.

Further, the ultraviolet LED epitaxial wafer further comprises a substrate, a buffer layer, an N-type semiconductor layer, an active layer, an electron blocking layer and a P-type semiconductor layer;

and the nucleation layer, the buffer layer, the N-type semiconductor layer, the active layer, the electron blocking layer and the P-type semiconductor layer are sequentially deposited on the substrate along the epitaxial growth direction.

Further, the temperature for growing the first nucleation layer is 800-900 ℃, and the temperature for growing the second nucleation layer is 1000-1100 ℃.

Further, the first nucleation layer is grown at a rate of less than 0.5 μm/h and the second nucleation layer is grown at a rate of greater than 1.5 μm/h.

Further, the pressure for growing the first nucleation layer is 150mbar to 250mbar, and the pressure for growing the second nucleation layer is 50mbar to 100mbar.

Further, the height of Gap of the first nucleation layer is 15-20 mm, and the height of Gap of the second nucleation layer is 8-12 mm.

Further, NH is introduced during the growth of the first nucleation layer ₃ The flow rate of the second nucleation layer is 18L-22L, NH is introduced during the growth of the second nucleation layer ₃ The flow rate of (2) is 2L to 4L.

Further, the thickness of the first nucleation layer is smaller than that of the second nucleation layer, wherein the thickness of the first nucleation layer is 1-10 nm, and the thickness of the second nucleation layer is 15-50 nm.

According to the preparation method of the ultraviolet LED epitaxial wafer, which is provided by the embodiment of the invention, the preparation method is used for preparing the ultraviolet LED epitaxial wafer and comprises the following steps:

sequentially depositing a first nucleation layer and a second nucleation layer along an epitaxial growth direction, wherein in the process of growing the first nucleation layer and the second nucleation layer, the temperature of the first nucleation layer is controlled to be lower than that of the second nucleation layer, the speed of the first nucleation layer is controlled to be lower than that of the second nucleation layer, the pressure of the first nucleation layer is controlled to be higher than that of the second nucleation layer, the Gap height of the first nucleation layer is controlled to be higher than that of the second nucleation layer, the height difference between the Gap height and the Gap height is controlled to be 5-9 mm when the first nucleation layer is grown, and NH is introduced when the first nucleation layer is controlled to be grown ₃ Is greater than NH is introduced during growth of the second nucleation layer ₃ And (3) after the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the substances with mixed crystals and multiple crystals, thereby obtaining the nucleation layer with clear surface morphology.

According to the embodiment of the invention, the LED chip comprises the ultraviolet LED epitaxial wafer.

The beneficial effects of the invention are as follows:

by arranging a nucleation layer which comprises a first nucleation layer and a second nucleation layer which are sequentially laminated, wherein the first nucleation layer and the second nucleation layer are AlN layers, the temperature for growing the first nucleation layer is lower than that for growing the second nucleation layer, the speed for growing the first nucleation layer is lower than that for growing the second nucleation layer, the pressure for growing the first nucleation layer is higher than that for growing the second nucleation layer, the Gap height of the first nucleation layer is higher than that of the second nucleation layer, and NH is introduced during the growth of the first nucleation layer ₃ Is greater than NH introduced during growth of the second nucleation layer ₃ After the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the impurity crystal and the polycrystalline substance to obtain a nucleation layer with clear surface morphology, specifically, the nucleation layerThe setting can lay a foundation for the growth of the subsequent buffer layer, is convenient for obtaining the buffer layer with better crystal quality, and finally achieves the aim of improving the internal quantum efficiency.

Drawings

Fig. 1 is a schematic structural diagram of an ultraviolet LED epitaxial wafer according to an embodiment of the present invention;

fig. 2 is a flowchart of a method for preparing an ultraviolet LED epitaxial wafer according to an embodiment of the present invention.

Detailed Description

In order that the invention may be readily understood, a more complete description of the invention will be rendered by reference to the appended drawings. Several embodiments of the invention are presented in the figures. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

It will be understood that when an element is referred to as being "mounted" on another element, it can be directly on the other element or intervening elements may also be present. When an element is referred to as being "connected" to another element, it can be directly connected to the other element or intervening elements may also be present. The terms "vertical," "horizontal," "left," "right," and the like are used herein for illustrative purposes only.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

Referring to fig. 1, a schematic structural diagram of an ultraviolet LED epitaxial wafer according to an embodiment of the present invention is provided, where the ultraviolet LED epitaxial wafer includes a substrate 1, and a nucleation layer 2, a buffer layer 3, an N-type semiconductor layer 4, an active layer 5, an electron blocking layer 6 and a P-type semiconductor layer 7 sequentially disposed on the substrate 1.

In the present embodiment, the substrate 1 may be a sapphire substrate, a SiC substrate, a Si-based substrate, a GaN substrate, or the like, and specifically, the nucleation layer 2 includes a first nucleation layer and a second nucleation layer which are sequentially stacked, the first nucleation layer and the second nucleation layer are all AlN layers, the thickness of the first nucleation layer is 1nm to 10nm, and the thickness of the first nucleation layer is 1nm, 2nm, 3nm, 4nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, or the like, by way of example, but not limited thereto; the thickness of the second nucleation layer is 15nm to 50nm, and exemplary, but not limited thereto, the thickness of the second nucleation layer is 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, 50nm, or the like; the buffer layer 3 is an AlN layer, and the thickness of the buffer layer 3 is 1 μm to 2 μm, and exemplary thicknesses of the buffer layer 3 are 1 μm, 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, or 2 μm, etc., but are not limited thereto; the N-type semiconductor layer 4 is N-type doped Al _x Ga _1-x The N layer, the dopant of the N-type semiconductor layer 4 may be Si, and the doping concentration of the N-type semiconductor layer 4 may be 5E18atoms/cm as the electron providing layer ³ ～1E20 atoms/cm ³ The Al component is 40% -60%, the thickness of the N-type semiconductor layer 4 is 1 μm to 3 μm, and the thickness of the N-type semiconductor layer 4 is 1 μm, 1.5 μm, 2 μm, 2.5 μm, or 3 μm, etc., by way of example, but not limited thereto; the active layer 5 includes a quantum well layer and a quantum barrier layer which periodically and alternately grow, wherein the quantum well layer and the quantum barrier layer are all AlGaN layers, the average Al component in the quantum well layer is 35%, the Al component in the quantum barrier layer is 50%, the growth period of the quantum well layer and the quantum barrier layer in the active layer 5 is 3 to 5, the thickness of the quantum well layer is 1nm to 3nm, and the thickness of the quantum well layer is 1nm, 1.5nm, 2nm, 2.5nm or 3nm, etc., by way of example, but not limited thereto; the thickness of the quantum barrier layer is 10nm to 14nm, and exemplary, but not limited thereto, the thickness of the quantum barrier layer is 10nm, 11nm, 12nm, 13nm, 14nm, or the like; the electron blocking layer 6 has a thickness of 20nm to 30nm, and in the ebl electron blocking layer, the Al component is 60% to 70%, and exemplary electron blocking layers 6 have a thickness of 20nm, 22nm, 25nm, 28nm, 30nm, or the like, but not limited thereto; the P-type semiconductor layer 7 is P-type doped Al _z Ga _1-z The doping agent of the N layer and the P type semiconductor layer 7 can be Mg, the Al component is 20-40%, and the doping concentration of the Mg can be 5E18atoms/cm ³ ～5E19 atoms/cm ³ The thickness of the P-type semiconductor layer 7 is 150nm to 250nm, and exemplary thicknesses of the P-type semiconductor layer 7 are 150nm, 180nm, 200nm, 220nm, 250nm, or the like, but are not limited thereto.

In the process of growing the nucleation layer 2, the temperature of the first nucleation layer is lower than the temperature of the second nucleation layer, the speed of the first nucleation layer is lower than the speed of the second nucleation layer, the pressure of the first nucleation layer is higher than the pressure of the second nucleation layer, the Gap height of the first nucleation layer is higher than the Gap height of the second nucleation layer, and the difference between the Gap height when the first nucleation layer is grown and the Gap height when the second nucleation layer is grown is 5mm to 9mm, and exemplary, but not limited thereto, the difference between the heights is 5mm, 6mm, 7mm, 8mm, 9mm, or the like. NH is introduced during the growth of the first nucleation layer ₃ Is greater than NH introduced during growth of the second nucleation layer ₃ After the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove impurity crystals and polycrystalline substances to obtain a nucleation layer with clear surface morphology, wherein the Gap height refers to the distance between the surface of the graphite disc and the top cover spray header, if the Gap is large, the relative Al component is lower, the growth speed is slower, the byproducts are more, and the temperature is relatively higher; the contrary is true for small Gap. It will be appreciated that the present invention employs a three-step process for growing nucleation layer 2, the first step being the growth of the first nucleation layer, the second step being the growth of the second nucleation layer, and the third step being a heat treatment.

Specifically, the temperature for growing the first nucleation layer is 800-900 ℃, the temperature for growing the second nucleation layer is 1000-1100 ℃, the speed for growing the first nucleation layer is less than 0.5 mu m/h, the speed for growing the second nucleation layer is more than 1.5 mu m/h, the pressure for growing the first nucleation layer is 150-250 mbar, the pressure for growing the second nucleation layer is 50-100 mbar, the Gap height for growing the first nucleation layer is 15-20 mm, the Gap height for growing the second nucleation layer is 8-12 mm, and NH is introduced when the first nucleation layer is grown ₃ The flow rate of (2) is 18L-22L, NH is introduced when the second nucleation layer is grown ₃ The flow rate of (2L) to (4L) was found to be a layer of seed crystals, i.e., nucleation, was deposited on the surface of the substrate 1Layer 2, intended to be subsequently lined with a high quality buffer layer 3, while the first nucleation layer is at low temperature, high pressure, high Gap height, large NH ₃ The seed crystal is spread on the surface of the substrate at low speed under the condition of high temperature, low pressure, low Gap height and small NH ₃ The purpose of rapid growth under flow is to rapidly form a second nucleation layer on the surface of the first nucleation layer, and then, after the growth of the first nucleation layer and the second nucleation layer is completed, heat treatment is performed to remove the impurity-crystalline and polycrystalline substances, thereby obtaining a nucleation layer 2 with clear surface morphology.

Wherein the heat treatment is carried out under the condition that the temperature for growing the second nucleation layer is raised to 1300-1400 ℃ at 1000-1100 ℃, and meanwhile, the Gap height, the pressure and the NH during the growth of the second nucleation layer are maintained ₃ The flow is unchanged, the MO source is not introduced, and the baking is carried out for 3 to 5 minutes.

Correspondingly, referring to fig. 2, the embodiment of the invention also provides a preparation method of the ultraviolet LED epitaxial wafer, which is used for preparing the ultraviolet LED epitaxial wafer, and specifically comprises the following steps:

s100: providing a substrate;

preferably, the selected substrate may be a silicon substrate, a sapphire substrate, a silicon carbide substrate or a GaN substrate, and in this embodiment, the substrate is a Si-based substrate, which has advantages of good thermal conductivity, low cost, mature process, easy peeling, and the like.

S200: sequentially depositing a nucleation layer, a buffer layer, an N-type semiconductor layer, an active layer, an electron blocking layer and a P-type semiconductor layer on a substrate along the epitaxial growth direction;

specifically, S200 includes:

s201: growing a nucleation layer on a Si-based substrate;

specifically, a MOCVD (Metal-organic Chemical Vapor Deposition, metal organic chemical vapor deposition) method is adopted to deposit a nucleation layer, wherein a first nucleation layer and a second nucleation layer are sequentially deposited along the epitaxial growth direction, and the temperature for growing the first nucleation layer is controlled to be lower than that for growing the second nucleation layer in the process of growing the first nucleation layer and the second nucleation layerThe temperature of the layers is controlled to control the speed of growing the first nucleation layer to be lower than the speed of growing the second nucleation layer, the pressure of growing the first nucleation layer to be higher than the pressure of growing the second nucleation layer, the Gap height of growing the first nucleation layer to be higher than the Gap height of growing the second nucleation layer, and NH is introduced during the growth of the first nucleation layer ₃ Is greater than NH introduced during growth of the second nucleation layer ₃ And (3) after the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the impurity crystal and the polycrystalline substance, and obtaining the nucleation layer with clear surface morphology.

Wherein the heat treatment is performed under the condition that the temperature is controlled to be raised from 1000 ℃ to 1100 ℃ to 1300 ℃ to 1400 ℃ when the second nucleation layer is grown, and meanwhile, the Gap height, the pressure and the NH when the second nucleation layer is grown are maintained ₃ The flow is unchanged, the MO source is not introduced, and the baking is carried out for 3 to 5 minutes.

The temperature for growing the first nucleation layer is 800-900 ℃, the temperature for growing the second nucleation layer is 1000-1100 ℃, the speed for growing the first nucleation layer is less than 0.5 mu m/h, the speed for growing the second nucleation layer is greater than 1.5 mu m/h, the pressure for growing the first nucleation layer is 150-250 mbar, the pressure for growing the second nucleation layer is 50-100 mbar, the Gap height for growing the first nucleation layer is 15-20 mm, the Gap height for growing the second nucleation layer is 8-12 mm, and NH is introduced when the first nucleation layer is grown ₃ The flow rate of (2) is 18L-22L, NH is introduced when the second nucleation layer is grown ₃ The flow rate of (2) is 2L to 4L.

S202: growing a buffer layer on the nucleation layer;

wherein, a buffer layer is deposited by adopting an MOCVD (Metal-organic Chemical Vapor Deposition, metal organic chemical vapor deposition) method, specifically, a Si-based substrate with a nucleation layer is put into an MOCVD reaction cavity, TMAL and NH are introduced into the reaction cavity ₃ The AlN buffer layer is prepared by a chemical vapor deposition method, in the process of preparing the AlN buffer layer, the temperature in an MOCVD reaction cavity is controlled to be 1200-1300 ℃, the pressure is controlled to be 50-100 mbar, ammonia gas is intermittently introduced into the reaction cavity after being opened for 30 seconds and closed for 10 seconds, and the thickness of the grown AlN layer is 1-2 mu m.

It should be noted thatThe purpose of growing an AlN layer at high temperature is mainly to release lattice mismatch and thermal mismatch of the substrate and AlGaN material. When an AlN layer is prepared by a common growth method, cracks appear. Thus, in the present embodiment, the AlN layer employs NH in a low-pressure high-temperature environment ₃ Pulsed-on preparation, i.e. continuous-on MO source (TMAL source and TMGa source), but NH ₃ The AlN layer with better crystal quality can be obtained by intermittently introducing the AlN into the reaction chamber in a pulse mode.

S203: growing an N-type semiconductor layer on the buffer layer;

specifically, an N-type semiconductor layer is grown in MOCVD equipment, wherein the N-type semiconductor layer is N-type doped Al _x Ga _1-x The N layer, the dopant of the N-type semiconductor layer may be Si, and the doping concentration of the N-type semiconductor layer may be 5E18atoms/cm as the electron supply layer ³ ～1E20 atoms/cm ³ The Al component is 40% -60%, the thickness of the N-type semiconductor layer is controlled to be 1-3 mu m, specifically, the temperature in the MOCVD reaction cavity is controlled to be 1000-1200 ℃ and the pressure is controlled to be 50-150 mbar.

S204: growing an active layer on the N-type semiconductor layer;

specifically, an active layer is grown in MOCVD equipment, the active layer comprises a quantum well layer and a quantum barrier layer which are periodically and alternately grown, wherein the quantum well layer and the quantum barrier layer are all AlGaN layers, the average Al component in the quantum well layer is 35%, the Al component in the quantum barrier layer is 50%, the growth period of the quantum well layer and the quantum barrier layer in the active layer is 3-5, the thickness of the quantum well layer is 1-3 nm, the thickness of the quantum barrier layer is 10-14 nm, the temperature in an MOCVD reaction cavity is controlled to be 1000-1200 ℃, and the pressure is controlled to be 50-150 mbar.

S205: growing an electron blocking layer on the active layer;

specifically, an electron blocking layer is grown in MOCVD equipment, the thickness of the deposited EBL electron blocking layer is controlled to be 20-30 nm, and the Al component is controlled to be 60-70%, wherein the temperature in the MOCVD equipment is controlled to be 1000-1200 ℃ and the pressure is controlled to be 50-150 mbar.

S206: growing a P-type semiconductor layer on the electron blocking layer;

specifically, growing a P-type semiconductor layer in MOCVD equipment, and controlling the thickness of the deposited P-type semiconductor layer to be 150-250 nm, wherein the P-type semiconductor layer is P-type doped Al _z Ga _1-z The doping agent of the N layer and the P type semiconductor layer can be Mg, the Al component is 20-40%, and the doping concentration of the Mg can be 5E18atoms/cm ³ ～5E19 atoms/cm ³ The temperature in MOCVD equipment is controlled to be 1000 ℃ to 1100 ℃ and the air pressure is controlled to be 50mbar to 200mbar.

When the embodiment is realized, trimethylgallium is used as a gallium source, high-purity ammonia gas is used as a nitrogen source, and high-purity H ₂ As carrier gas, trimethylaluminum is used as aluminum source, silane is used as N-type dopant, and magnesium is used as P-type dopant.

The invention is further illustrated by the following examples:

example 1

The embodiment provides an ultraviolet LED epitaxial wafer, which comprises a substrate, and a nucleation layer, a buffer layer, an N-type semiconductor layer, an active layer, an electron blocking layer and a P-type semiconductor layer which are sequentially arranged on the substrate.

In this embodiment, the substrate is a Si-based substrate, specifically, the thickness of the first nucleation layer in the nucleation layer is 5nm, the thickness of the second nucleation layer in the nucleation layer is 50nm, and the N-type semiconductor layer is N-type doped Al _x Ga _1-x An N layer, the dopant of the N-type semiconductor layer may be Si, and the doping concentration of the N-type semiconductor layer may be 1E19atoms/cm as the electron supply layer ³ The Al component is 50%, the thickness of the N-type semiconductor layer is 2 mu m, the active layer comprises a quantum well layer and a quantum barrier layer which are periodically and alternately grown, wherein the quantum well layer and the quantum barrier layer are all AlGaN layers, the average Al component in the quantum well layer is 35%, the Al component in the quantum barrier layer is 50%, the growth period of the quantum well layer and the quantum barrier layer in the active layer is 5, the thickness of the quantum well layer is 2nm, the thickness of the quantum barrier layer is 12nm, the thickness of the electron barrier layer is 25nm, the Al component in the electron barrier layer is 65%, and the P-type semiconductor layer is P-type doped Al _z Ga _1-z The dopant of the N layer and the P type semiconductor layer can be Mg, the Al component is 30 percent, and the doping concentration of the MgMay be 5E19 atoms/cm ³ The thickness of the P-type semiconductor layer was 200nm.

The preparation method of the ultraviolet LED epitaxial wafer in the embodiment comprises the following steps:

(1) Providing a Si-based substrate;

in the embodiment, the substrate is a Si-based substrate, and the Si-based substrate has the advantages of good heat conductivity, low cost, mature process, easy stripping and the like.

(2) Growing a nucleation layer on a Si-based substrate;

specifically, a nucleation layer is deposited by MOCVD (Metal-organic Chemical Vapor Deposition, metal organic chemical vapor deposition) method, wherein a Si-based substrate is placed in an MOCVD reaction chamber, and TMAL and NH are introduced into the reaction chamber ₃ The nucleation layer is prepared by chemical vapor deposition. When the growth of the first nucleation layer is controlled, the temperature is 800 ℃ and the NH is controlled ₃ The flow is 20L, the pressure is 200mbar, the gap height is 16mm, the growth rate is 0.2 mu m/h, the growth thickness is 5nm, after the growth of the first nucleation layer is finished, the temperature in the MOCVD reaction cavity is raised to 1050 ℃, and simultaneously, the pressure is reduced to 50mbar, NH ₃ A second nucleation layer with a flow rate of 3L, a Gap height of 11mm, a growth rate of 1.5 μm/h and a growth thickness of 50nm, wherein the difference between the height of the Gap for growing the first nucleation layer and the height of the Gap for growing the second nucleation layer is 5mm; after the growth of the second nucleation layer is finished, the temperature in the MOCVD reaction chamber is increased to 1350 ℃ again, and the Gap height and NH are maintained ₃ Flow rate is unchanged, i.e. NH ₃ The flow is 3L, the gap height is 11mm, TMAL is closed, and baking is carried out for 5min, so that the nucleation layer is finally obtained.

(3) Growing a buffer layer on the nucleation layer;

wherein, a buffer layer is deposited by adopting an MOCVD (Metal-organic Chemical Vapor Deposition, metal organic chemical vapor deposition) method, specifically, a Si-based substrate with a nucleation layer is put into an MOCVD reaction cavity, TMAL and NH are introduced into the reaction cavity ₃ Preparing an AlN buffer layer by a chemical vapor deposition method, controlling the temperature in an MOCVD reaction cavity to 1250 ℃ and the pressure to 50mbar in the process of preparing the AlN buffer layer, and intermittently introducing ammonia gas into the reaction cavity for 30 seconds and 10 seconds to produce the AlN buffer layerThe thickness of the long AlN layer was 1.5. Mu.m.

The purpose of growing the AlN layer at high temperature is mainly to release lattice mismatch and thermal mismatch of the substrate and AlGaN material. When an AlN layer is prepared by a common growth method, cracks appear. Thus, in the present embodiment, the AlN layer employs NH in a low-pressure high-temperature environment ₃ Pulsed-on preparation, i.e. continuous-on MO source (TMAL source and TMGa source), but NH ₃ The AlN layer with better crystal quality can be obtained by intermittently introducing the AlN into the reaction chamber in a pulse mode.

(4) Growing an N-type semiconductor layer on the buffer layer;

specifically, an N-type semiconductor layer is grown in MOCVD equipment, wherein the N-type semiconductor layer is N-type doped Al _x Ga _1-x An N layer, the dopant of the N-type semiconductor layer may be Si, and the doping concentration of the N-type semiconductor layer may be 1E19atoms/cm as the electron supply layer ³ The Al component was 50%, the thickness of the N-type semiconductor layer was controlled to 2. Mu.m, specifically, the temperature in the MOCVD reaction chamber was controlled to 1100℃and the pressure was controlled to 100mbar.

(5) Growing an active layer on the N-type semiconductor layer;

specifically, an active layer is grown in MOCVD equipment, the active layer comprises a quantum well layer and a quantum barrier layer which are periodically and alternately grown, wherein the quantum well layer and the quantum barrier layer are all AlGaN layers, the average Al component in the quantum well layer is 35%, the Al component in the quantum barrier layer is 50%, the growth period of the quantum well layer and the quantum barrier layer in the active layer is 5, the thickness of the quantum well layer is 2nm, the thickness of the quantum barrier layer is 12nm, the temperature in an MOCVD reaction cavity is controlled to be 1080 ℃, and the pressure is 100mbar.

(6) Growing an electron blocking layer on the active layer;

specifically, an electron blocking layer was grown in an MOCVD apparatus, the thickness of the deposited EBL electron blocking layer was controlled to 25nm, and the Al composition was controlled to 65%, wherein the temperature in the MOCVD apparatus was controlled to 1100℃and the pressure was controlled to 100mbar.

(7) Growing a P-type semiconductor layer on the electron blocking layer;

specifically, P-type semiconductors are grown in MOCVD apparatusA bulk layer controlling the thickness of the deposited P-type semiconductor layer to be 200nm, wherein the P-type semiconductor layer is P-type doped Al _z Ga _1-z The dopant of the N layer and the P type semiconductor layer can be Mg, the Al component is 30 percent, and the doping concentration of the Mg can be 5E19 atoms/cm ³ The temperature in the MOCVD apparatus was controlled to 1050℃and the gas pressure to 100mbar.

When the embodiment is realized, trimethylgallium is used as a gallium source, high-purity ammonia gas is used as a nitrogen source, and high-purity H ₂ As carrier gas, trimethylaluminum is used as aluminum source, silane is used as N-type dopant, and magnesium is used as P-type dopant.

Example two

The embodiment also provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that NH is always maintained in the process of growing the nucleation layer in the second embodiment ₃ The flow rate was 20L and the pressure 200mbar.

Example III

The embodiment also provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that NH is always maintained in the process of growing the nucleation layer in the third embodiment ₃ The flow rate was 3L.

Example IV

The present embodiment also provides an ultraviolet LED epitaxial wafer and a method for manufacturing the same, which are different from the first embodiment in that in the process of growing the nucleation layer in the fourth embodiment, the height of Gap is 17mm when the first nucleation layer is grown, the height of Gap is 11mm when the second nucleation layer is grown, and the height difference is 6mm.

Example five

The embodiment also provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that in the process of growing the nucleation layer in the fifth embodiment, the height of Gap is 18mm when the first nucleation layer is grown, the height of Gap is 11mm when the second nucleation layer is grown, and the height difference is 7mm.

Example six

The embodiment also provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that in the process of growing the nucleation layer in the fifth embodiment, the height of Gap is 19mm when the first nucleation layer is grown, the height of Gap is 11mm when the second nucleation layer is grown, and the height difference is 8mm.

Example seven

The present embodiment also provides an ultraviolet LED epitaxial wafer and a method for manufacturing the same, which are different from the first embodiment in that in the process of growing the nucleation layer in the sixth comparative embodiment, the height of Gap is 20mm when the first nucleation layer is grown, the height of Gap is 11mm when the second nucleation layer is grown, and the height difference is 9mm.

Comparative example one

The comparison example provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that a two-step method is adopted to grow a nucleation layer in the first comparison example, namely, the step of heat treatment is omitted, in addition, the growth temperature of the first nucleation layer is controlled to be 800 ℃, the growth temperature of the second nucleation layer is controlled to be 1350 ℃, and NH is always maintained ₃ The flow rate was 20L and the pressure was 200mbar, controlling the thickness of both the first and second nucleation layers to be 5nm.

Comparative example two

The comparison example provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that a two-step method is adopted to grow a nucleation layer in the second comparison example, namely, the step of heat treatment is omitted, in addition, the growth temperature of the first nucleation layer is controlled to 1050 ℃, the growth temperature of the second nucleation layer is controlled to 1350 ℃, and NH is always maintained ₃ The flow rate was 3L and the pressure was 200mbar, controlling the thickness of both the first and second nucleation layers to be 5nm.

Comparative example three

The comparison example provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that a nucleation layer is grown in one step in the third comparison example, namely the nucleation layer is directly grown, wherein the growth temperature of the nucleation layer is 800 ℃, and NH is always maintained ₃ The flow was 20L and the pressure was 200mbar, controlling the thickness of the nucleation layer to be 5nm.

Comparative example four

The comparative example provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first example in that a nucleation layer is grown in one step in the fourth comparative example, namely the nucleation layer is directly grown, whereinThe growth temperature of the nucleation layer is 1050 ℃, and NH is always maintained ₃ The flow was 20L and the pressure was 200mbar, controlling the thickness of the nucleation layer to be 5nm.

Comparative example five

The comparative example also provides an ultraviolet LED epitaxial wafer and a method for manufacturing the same, which are different from the first example in that the height of Gap is 15mm when the first nucleation layer is grown and the height of Gap is 11mm when the second nucleation layer is grown in the process of growing the nucleation layer in the fifth comparative example, and the height difference is 4mm.

Prior Art

The prior art provides an ultraviolet LED epitaxial wafer and a preparation method thereof, which are different from the first embodiment in that the ultraviolet LED epitaxial wafer has no nucleation layer structure.

The LED chips prepared from the ultraviolet LED epitaxial wafers of the examples one to seven, the comparative examples one to five and the prior art were tested under the same conditions (test current 100 mA), and specific results are as follows:

as can be seen from the table, under the same test conditions, the LED chip prepared by the method in the embodiment of the invention has effectively improved forward luminescence brightness and 14mw maximum forward luminescence brightness compared with the LED chip prepared by the comparative example and the prior art, and meanwhile, the yield of the LED chip prepared by the method in the embodiment of the invention is better than that of the traditional method.

The embodiment of the invention also provides an LED chip, which comprises the ultraviolet LED epitaxial wafer.

In summary, the ultraviolet LED epitaxial wafer, the preparation method and the LED chip in the embodiment of the invention are characterized in that the nucleation layer comprises a first nucleation layer and a second nucleation layer which are sequentially laminated, wherein the first nucleation layer and the second nucleation layer are AlN layers, the temperature for growing the first nucleation layer is lower than that for growing the second nucleation layer, and the speed for growing the first nucleation layer is lower than that of growing the first nucleation layerGrowing the second nucleation layer at a higher speed, and introducing NH when growing the first nucleation layer, wherein the pressure for growing the first nucleation layer is higher than the pressure for growing the second nucleation layer, and the Gap height of the grown first nucleation layer is higher than the Gap height of the grown second nucleation layer ₃ Is greater than NH introduced during growth of the second nucleation layer ₃ After the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove impurity crystals and polycrystalline substances, thereby obtaining a nucleation layer with clear surface morphology.

The foregoing examples illustrate only a few embodiments of the invention and are described in detail herein without thereby limiting the scope of the invention. It should be noted that it will be apparent to those skilled in the art that several variations and modifications can be made without departing from the spirit of the invention, which are all within the scope of the invention. Accordingly, the scope of protection of the present invention is to be determined by the appended claims.

Claims (10)

1. The ultraviolet LED epitaxial wafer is characterized by comprising a nucleation layer, wherein the nucleation layer comprises a first nucleation layer and a second nucleation layer which are sequentially laminated, the first nucleation layer and the second nucleation layer are AlN layers, the temperature for growing the first nucleation layer is lower than that for growing the second nucleation layer, the speed for growing the first nucleation layer is lower than that for growing the second nucleation layer, the pressure for growing the first nucleation layer is higher than that for growing the second nucleation layer, the Gap height of the first nucleation layer is higher than that for growing the second nucleation layer, the difference between the Gap height when the first nucleation layer is grown and the Gap height when the second nucleation layer is grown is 5-9 mm, and NH is introduced when the first nucleation layer is grown ₃ Is greater than NH is introduced during growth of the second nucleation layer ₃ After the growth of the first and second nucleation layers is completed, performing a heat treatment to remove hetero-and poly-crystalline statesAnd obtaining the substance to obtain the nucleation layer with clear surface morphology.

2. The ultraviolet LED epitaxial wafer of claim 1, further comprising a substrate, a buffer layer, an N-type semiconductor layer, an active layer, an electron blocking layer, and a P-type semiconductor layer;

and the nucleation layer, the buffer layer, the N-type semiconductor layer, the active layer, the electron blocking layer and the P-type semiconductor layer are sequentially deposited on the substrate along the epitaxial growth direction.

3. The uv LED epitaxial wafer of claim 1 or 2, wherein the temperature at which the first nucleation layer is grown is 800-900 ℃ and the temperature at which the second nucleation layer is grown is 1000-1100 ℃.

4. The uv LED epitaxial wafer of claim 1 or 2, wherein the first nucleation layer is grown at a rate of less than 0.5 μm/h and the second nucleation layer is grown at a rate of greater than 1.5 μm/h.

5. The uv LED epitaxial wafer of claim 1 or 2, wherein the pressure at which the first nucleation layer is grown is 150mbar to 250mbar and the pressure at which the second nucleation layer is grown is 50mbar to 100mbar.

6. The ultraviolet LED epitaxial wafer of claim 1 or 2, wherein the height of the Gap for growing the first nucleation layer is 15mm to 20mm and the height of the Gap for growing the second nucleation layer is 8mm to 12mm.

7. The ultraviolet LED epitaxial wafer of claim 1 or 2, wherein NH is introduced during growth of the first nucleation layer ₃ The flow rate of the second nucleation layer is 18L-22L, NH is introduced during the growth of the second nucleation layer ₃ The flow rate of (2) is 2L to 4L.

8. The ultraviolet LED epitaxial wafer of claim 1 or 2, wherein the thickness of the first nucleation layer is less than the thickness of the second nucleation layer, wherein the thickness of the first nucleation layer is 1nm to 10nm and the thickness of the second nucleation layer is 15nm to 50nm.

9. A method for preparing an ultraviolet LED epitaxial wafer, which is used for preparing the ultraviolet LED epitaxial wafer according to any one of claims 1 to 8, the method comprising:

sequentially depositing a first nucleation layer and a second nucleation layer along an epitaxial growth direction, wherein in the process of growing the first nucleation layer and the second nucleation layer, the temperature of the first nucleation layer is controlled to be lower than that of the second nucleation layer, the speed of the first nucleation layer is controlled to be lower than that of the second nucleation layer, the pressure of the first nucleation layer is controlled to be higher than that of the second nucleation layer, the Gap height of the first nucleation layer is controlled to be higher than that of the second nucleation layer, the height difference between the Gap height and the Gap height is controlled to be 5-9 mm when the first nucleation layer is grown, and NH is introduced when the first nucleation layer is controlled to be grown ₃ Is greater than NH is introduced during growth of the second nucleation layer ₃ And (3) after the growth of the first nucleation layer and the second nucleation layer is completed, performing heat treatment to remove the substances with mixed crystals and multiple crystals, thereby obtaining the nucleation layer with clear surface morphology.

10. An LED chip comprising the ultraviolet LED epitaxial wafer of any one of claims 1 to 8.