LED epitaxial wafer grown on molybdenum unconventional substrate and preparation method thereof

Abstract

The present application relates to a kind of LED epitaxial wafer grown in molybdenum unconventional substrate and its preparation method.The epitaxial wafer includes successively from bottom to top: molybdenum substrate, molybdenum carbide buffer layer, GaN layer, n-GaN layer, multiple quantum well layer and p-GaN layer.The present application also provides the preparation method of the epitaxial wafer.The present application prepares molybdenum carbide buffer layer on molybdenum substrate, and molybdenum carbide buffer layer is due to surface roughness, enhances backscattering light, greatly improves the luminous efficiency of LED.Secondly, molybdenum carbide buffer layer is easy to be corroded, so that molybdenum substrate can be reused.Finally, molybdenum carbide buffer layer can obtain very low lattice mismatch degree between substrate and GaN epitaxial layer, overcome the problem that hexagonal GaN is difficult to grow directly on molybdenum, and reduce lattice mismatch degree, reduce the stress between GaN epitaxial layer and molybdenum substrate, improve the performance of LED chip.

Description

TECHNICAL FIELD

[0001] The present application relates to a LED epitaxial wafer grown on a molybdenum unconventional substrate and a preparation method thereof, and belongs to the field of optoelectronic technology. BACKGROUND

[0002] GaN as the third generation semiconductor material, has a wide band gap, high electron mobility and good thermal conductivity and other excellent properties, can be widely used in optoelectronic semiconductor, high mobility semiconductor and other devices. In the field of semiconductor lighting, based on GaN prepared light emitting diode (LED) has become the mainstream of the lighting market. After decades of development, sapphire substrate and SiC substrate have become mature commercialized GaN-based LED epitaxial substrate. Sapphire substrate is a single crystal Al2O3 material, with its excellent chemical stability and high hardness as the mainstream substrate of GaN-based LED epitaxy. However, with the large-scale application of GaN-based LED, how to reduce the preparation cost of LED has also become the focus of the market.

[0003] However, there are many disadvantages in the preparation of sapphire substrate GaN-based LED chip. First, the thermal conductivity of sapphire substrate is low, which makes the temperature generated during the operation of LED cannot be conducted in time, and the high temperature affects the performance and reliability of the device, which is particularly serious in the application of high-power devices. Second, the electrical conductivity of sapphire substrate is low, which means that the chip of LED must adopt the same side electrode structure of the lateral structure chip, and cannot be directly made into a vertical structure. Compared with the traditional lateral structure LED, the vertical structure LED has many advantages: (1) the P and N electrodes of the planar structure LED are on the same side, and the current flows laterally in the n-type and p-type GaN confinement layer, which leads to uneven current distribution, resulting in current crowding and high heat generation. The vertical structure LED has two electrodes on the upper and lower sides of the LED epitaxial layer, and the current flows vertically through the epitaxial layer, without lateral current flow, so the current distribution is uniform and the heat generated is reduced. (2) The traditional lateral structure adopts sapphire substrate, which is not conductive, so the mesa needs to be etched, sacrificing the area of the active region. In addition, due to the poor thermal conductivity of sapphire substrate, the heat dissipation of LED chip is limited; if the sapphire substrate is removed by bonding and peeling method, the sapphire substrate must be replaced with a substrate with good electrical conductivity and high thermal conductivity, but the process is complex.

[0004] Compared with the vertical structure of the conventional semiconductor device, the preparation process of the lateral structure LED chip is complex and the cost is high; on the other hand, the lateral structure chip is weakened in current transmission and light emitting area, which reduces the performance of the device. For epitaxial growth, there are also some problems with the sapphire substrate. First, the lattice mismatch between the sapphire substrate and GaN is as high as 15%, which causes a certain tensile stress during the epitaxial process. In order to release this stress, a large number of dislocation defects will be generated in the GaN layer. These dislocations form non-radiative recombination centers in the active layer, which reduces the internal quantum efficiency of the LED. Second, the thermal mismatch between sapphire and GaN is about 25.5%, which will introduce compressive stress during the epitaxial cooling process. For a relatively thick film without optimized process, it is easy to cause cracks in the GaN and sapphire substrate, which affects the use and stability of the device.

[0005] Chinese patent document CN109545921A discloses an LED chip, an LED epitaxial wafer and a preparation method thereof, wherein the LED epitaxial wafer can include a metal substrate, a GaN nucleation layer arranged on the surface of the metal substrate, an N-type GaN layer arranged on the surface of the GaN nucleation layer, a multi-quantum well layer arranged on the surface of the N-type GaN layer, a GaN barrier layer arranged on the surface of the multi-quantum well layer, and a P-type GaN layer arranged on the surface of the GaN barrier layer. However, directly growing GaN on nickel will cause serious interface reaction and huge thermal stress between the substrate due to the large difference in lattice matching degree, thereby seriously affecting the performance of the LED chip. Moreover, nickel is a face-centered cubic structure, while the commonly grown GaN is a wurtzite hexagonal crystal, so it is very difficult and complex to directly grow a hexagonal GaN on nickel. SUMMARY

[0006] In view of the deficiencies of the prior art, the purpose of the present application is to provide an LED epitaxial wafer grown on a molybdenum unconventional substrate and a preparation method thereof. The present application adopts a low-temperature growth process to epitaxially grow a GaN layer on a Mo (molybdenum) new substrate, thereby obtaining a high-quality LED epitaxial wafer. The Mo (molybdenum) substrate used has a simple growth process and a low price, which can greatly reduce the manufacturing cost of the device. By selecting a suitable crystal orientation, the high-quality GaN epitaxial obtained on the Mo (molybdenum) (111) crystal surface substrate can greatly improve the efficiency of the nitride LED. Meanwhile, the LED epitaxial wafer grown by the present application can be easily peeled off without damage.

[0007] The technical scheme of the present application is as follows:

[0008] An LED epitaxial wafer grown on a molybdenum unconventional substrate, from bottom to top, includes a molybdenum substrate, a molybdenum carbide buffer layer, a GaN layer, an n-GaN layer, a multi-quantum well layer and a p-GaN layer.

[0009] Preferably, the thickness of the molybdenum carbide buffer layer is 20-500 nm.

[0010] Preferably, the thickness of the GaN layer is 500-2000 nm.

[0011] Preferably, the thickness of the n-GaN layer is 1000-3000 nm.

[0012] Preferably, the multi-quantum well layer is an InGaN / GaN multi-quantum well layer.

[0013] Preferably, in the InGaN / GaN multi-quantum well layer, the thickness of the InGaN well layer is 3-5 nm, and the thickness of the GaN barrier layer is 10-15 nm.

[0014] Preferably, the InGaN / GaN multi-quantum well layer has a structure of 8-20 periods.

[0015] Preferably, the thickness of the p-GaN layer is 100-200 nm.

[0016] A method for preparing an LED epitaxial wafer grown on a molybdenum unconventional substrate, comprising the following steps:

[0017] Metallic molybdenum is used as a substrate, and a (111) crystal plane is used as an epitaxial surface. The surface of the molybdenum substrate is then polished, cleaned and subjected to high-temperature pretreatment. Subsequently, a molybdenum carbide (MoC) buffer layer, a GaN layer, an n-GaN layer, a multi-quantum well layer and a p-GaN layer are successively epitaxially grown on the molybdenum substrate, thereby obtaining an LED epitaxial wafer grown on a molybdenum unconventional substrate.

[0018] Preferably, the method for preparing the LED epitaxial wafer grown on a molybdenum unconventional substrate comprises the following steps:

[0019] (1) Molybdenum is used as a substrate, and a (111) crystal plane is used as an epitaxial surface.

[0020] (2) The surface of the molybdenum substrate is polished and cleaned, and then the molybdenum substrate is placed in a growth chamber of a MOCVD device, heated to 900-1000 ℃ in an H2 environment, and subjected to high-temperature surface pretreatment.

[0021] (3) The temperature is reduced to 600-680 ℃, the pressure in the reaction chamber is 30-70 Torr, the carbon source flow rate is 100-200 sccm, and the molybdenum source flow rate is 80-200 sccm, so as to grow a molybdenum carbide buffer layer on the molybdenum substrate.

[0022] (4) keeping the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, the V / III value at 80-120, and growing the GaN layer on the molybdenum carbide buffer layer;

[0023] (5) keeping the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, the V / III value at 80-120, and growing the n-GaN layer on the GaN layer;

[0024] (6) keeping the temperature at 600-800℃, the reaction chamber pressure at 100-300 Torr, the V / III value at 500-1000, and growing the InGaN / GaN multi-quantum well layer on the n-GaN layer;

[0025] (7) keeping the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, the V / III value at 80-200, and growing the p-GaN layer on the InGaN / GaN multi-quantum well layer, to obtain the LED epitaxial wafer grown on the molybdenum unconventional substrate.

[0026] The details of the present application are conventional prior art.

[0027] Beneficial effects:

[0028] 1. The present application prepares the molybdenum carbide buffer layer on the molybdenum substrate. Firstly, the smooth surface of the molybdenum substrate can reflect the light passing through the substrate surface, and the molybdenum carbide buffer layer enhances the backscattered light due to the rough surface, greatly improving the light emitting efficiency of the LED. Secondly, the molybdenum carbide buffer layer is easy to be etched, and the peeling of the molybdenum substrate and the LED epitaxial structure can be easily realized. The peeled molybdenum substrate can be reused, reducing the cost. Finally, the present application first prepares the molybdenum carbide buffer layer on the molybdenum substrate, and then continues to grow the GaN epitaxial layer on the molybdenum carbide buffer layer. The molybdenum carbide buffer layer can obtain a very low lattice mismatch between the substrate and the GaN epitaxial layer, overcoming the difficulty of directly growing hexagonal GaN on nickel, and reducing the lattice mismatch, reducing the stress between the GaN epitaxial layer and the molybdenum substrate, and improving the performance of the LED chip.

[0029] 2、The application uses metal molybdenum as a substrate, and prepares a molybdenum carbide buffer layer on the molybdenum substrate. Firstly, molybdenum has high thermal conductivity, which can conduct the heat generated in the LED chip in time to reduce the junction temperature of the device and improve the internal quantum efficiency of the device, which also helps to solve the heat dissipation problem of the device. Secondly, molybdenum can be used as a substrate material for growing a GaN-based vertical structure LED device. A back electrode can be directly plated on the molybdenum substrate without the need to etch the p-GaN layer and the active layer to connect the electrode to the n-GaN layer. In this way, the material of the active layer is fully utilized, and the anode material is plated on the p-GaN layer, so that the current almost entirely flows vertically through the GaN-based epitaxial layer, thereby reducing the resistance, avoiding current congestion, and uniformly distributing the current, reducing the heat generated by the current, and further solving the heat dissipation problem of the LED epitaxial wafer and improving the service life of the LED device. Finally, molybdenum is selected as the substrate, which has the advantages of being easy to obtain and cheap, which is beneficial to reducing the production cost.

[0030] 3、The preparation method of the LED epitaxial wafer grown on the molybdenum unconventional substrate provided by the application is simple and easy to operate, has repeatability, and the GaN-based LED epitaxial wafer grown by epitaxy has low defect density, high crystal quality, excellent electrical and optical properties, and the like. It can be widely applied in the field of LED and the like, and is convenient for popularization and application. BRIEF DESCRIPTION OF DRAWINGS

[0031] Figure 1 is a structural schematic diagram of the LED epitaxial wafer prepared in Example 1 in the application. DETAILED DESCRIPTION

[0032] The application will be further described below in combination with examples and drawings.

[0033] The raw materials used in the examples are all conventional raw materials and are commercially available unless otherwise specified. The methods used are all existing methods unless otherwise specified.

[0034] Example 1

[0035] As shown in Figure 1 , a LED epitaxial wafer grown on a molybdenum unconventional substrate comprises, from bottom to top, a molybdenum substrate, a molybdenum carbide buffer layer, a GaN layer, an n-GaN layer, a multi-quantum well layer, and a p-GaN layer.

[0036] The LED epitaxial wafer grown on the molybdenum unconventional substrate comprises the following steps:

[0037] (1) Molybdenum is used as a substrate with a (111) crystal surface as an epitaxial surface;

[0038] (2) The surface of the molybdenum substrate is polished and cleaned, and then the molybdenum substrate is placed in the growth chamber of the MOCVD equipment, and heated to 950℃ in a H2 environment for high-temperature pretreatment;

[0039] (3) the temperature is reduced to 650℃, the reaction chamber pressure is 50 Torr, the carbon source is 100 sccm, the molybdenum source flow is 150 sccm, and a molybdenum carbide buffer layer with a thickness of 100 nm is grown on the molybdenum substrate;

[0040] (4) the temperature is kept at 650℃, the reaction chamber pressure is 50 Torr, the V / III value is 100, and a GaN layer with a thickness of 1000 nm is grown on the molybdenum buffer layer;

[0041] (5) the temperature is kept at 650℃, the reaction chamber pressure is 200 Torr, the V / III value is 100, and an n-GaN layer with a thickness of 2000 nm is grown on the u-GaN layer;

[0042] (6) the temperature is kept at 650℃, the reaction chamber pressure is 200 Torr, the V / III value is 800, and an InGaN / GaN multi-quantum well layer is grown on the n-GaN layer; the InGaN well layer in the InGaN / GaN multi-quantum well layer has a thickness of 4 nm, the GaN barrier layer has a thickness of 12 nm, and the InGaN / GaN multi-quantum well layer has a 12-period structure;

[0043] (7) the temperature is kept at 650℃, the reaction chamber pressure is 200 Torr, the V / III value is 100, and a p-GaN layer with a thickness of 150 nm is grown on the InGaN / GaN multi-quantum well layer, thereby obtaining an LED epitaxial wafer grown on a molybdenum unconventional substrate.

[0044] Since the hydrofluoric acid does not corrode the molybdenum and the GaN layer but can corrode the molybdenum carbide buffer layer, the LED epitaxial wafer prepared in the embodiment can be used to corrode the molybdenum carbide buffer layer with the hydrofluoric acid, so as to realize the peeling of the molybdenum substrate and the LED epitaxial structure, and the peeled substrate can be repeatedly used, thereby reducing the cost.

[0045] Example 2

[0046] An LED epitaxial wafer grown on a molybdenum unconventional substrate, the structure and the preparation method of which are as described in the embodiment 1, except that the thickness of the molybdenum buffer layer is 20 nm, the thickness of the GaN layer is 500 nm, the thickness of the n-GaN layer is 1000 nm, the thickness of the InGaN well layer in the InGaN / GaN multi-quantum well layer is 3 nm, the thickness of the GaN barrier layer is 10 nm, the InGaN / GaN multi-quantum well layer has a 20-period structure, and the thickness of the p-GaN layer is 100 nm.

[0047] Example 3

[0048] An LED epitaxial wafer grown on a molybdenum unconventional substrate, the structure and preparation method are as described in Embodiment 1, except that: the thickness of the molybdenum buffer layer is 500 nm, the thickness of the GaN layer is 2000 nm, the thickness of the n-GaN layer is 3000 nm, the thickness of the InGaN well layer in the InGaN / GaN multi-quantum well layer is 5 nm, the thickness of the GaN barrier layer is 15 nm, the InGaN / GaN multi-quantum well layer is an 8-period structure, and the thickness of the p-GaN layer is 200 nm.

[0049] Comparative Example 1

[0050] An LED chip was prepared according to the disclosure of Chinese patent document CN109545921A.

[0051] Test Example

[0052] The LED epitaxial wafer prepared in Embodiment 1 and the LED chip prepared in Comparative Example 1 were subjected to laser testing;

[0053] The specific method is as follows: the LED epitaxial wafer is welded to a Cu heat sink and a ceramic heat spreader. Using a bar comprehensive performance tester, pulse testing is carried out at room temperature under a test current of 20 A. The test data are shown in Table 1 below:

[0054] Table 1

[0055] Group Power (mW) Voltage (V) Example 1 28.6 2.89 Comparative Example 1 24.1 3.01

[0056] As can be seen from Table 1, by the preparation method of first preparing a molybdenum carbide buffer layer on a molybdenum substrate and then growing a GaN epitaxial layer on the molybdenum carbide buffer layer, the performance of the LED epitaxial wafer of the present application is significantly improved. The power of the LED epitaxial wafer grown on a molybdenum unconventional substrate prepared in Embodiment 1 is increased by about 18.9% and the voltage is reduced by about 4% compared with the power of the LED chip of Comparative Example 1.

Claims

1. An LED epitaxial wafer grown on an unconventional molybdenum substrate, characterized in that, From bottom to top, it includes: a molybdenum substrate, a molybdenum carbide buffer layer, a GaN layer, an n-GaN layer, a multiple quantum well layer, and a p-GaN layer; The thickness of the molybdenum carbide buffer layer is 20~500nm; The method for preparing the LED epitaxial wafer grown on an unconventional molybdenum substrate includes the following steps: Using molybdenum as a substrate and the (111) crystal plane as the epitaxial plane, the surface of the molybdenum substrate is polished, cleaned and pretreated at high temperature. Then, the molybdenum carbide buffer layer, GaN layer, n-GaN layer, multiple quantum well layer and p-GaN layer are epitaxially grown on the molybdenum substrate in sequence to obtain the LED epitaxial wafer grown on the unconventional molybdenum substrate.

2. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 1, characterized in that, The thickness of the GaN layer is 500~2000nm.

3. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 1, characterized in that, The thickness of the n-GaN layer is 1000~3000nm.

4. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 1, characterized in that, The multiple quantum well layer is an InGaN / GaN multiple quantum well layer.

5. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 4, characterized in that, In the InGaN / GaN multiple quantum well layer, the thickness of the InGaN well layer is 3~5nm, and the thickness of the GaN barrier layer is 10~15nm.

6. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 4, characterized in that, The InGaN / GaN multiple quantum well layer has an 8-20 periodic structure.

7. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 1, characterized in that, The thickness of the p-GaN layer is 100~200nm.

8. The LED epitaxial wafer grown on an unconventional molybdenum substrate as described in claim 1, characterized in that, The method for preparing the LED epitaxial wafer grown on an unconventional molybdenum substrate specifically includes the following steps: (1) Molybdenum is used as the substrate and the (111) crystal plane is used as the epitaxial plane; (2) Polish and clean the surface of the molybdenum substrate, and then place the molybdenum substrate in the growth chamber of the MOCVD equipment and heat it to 900~1000℃ in H2 environment for high-temperature surface pretreatment; (3) Reduce the temperature to 600-680℃, the reaction chamber pressure to 30-70 Torr, the carbon source flow rate to 100-200 sccm, the molybdenum source flow rate to 80-200 sccm, and grow a molybdenum carbide buffer layer on the molybdenum substrate. (4) Maintain the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, and the V / III value at 80-120 to grow a GaN layer on the molybdenum carbide buffer layer; (5) Maintain the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, and the V / III value at 80-120 to grow an n-GaN layer on the GaN layer; (6) Maintain the temperature at 600-800℃, the reaction chamber pressure at 100-300 Torr, and the V / III value at 500-1000 to grow an InGaN / GaN multi-quantum well layer on the n-GaN layer; (7) Maintain the temperature at 600-680℃, the reaction chamber pressure at 100-300 Torr, and the V / III value at 80-200 to grow a p-GaN layer on the InGaN / GaN multi-quantum-well layer to obtain an LED epitaxial wafer grown on a molybdenum unconventional substrate.

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