Epitaxial structure for reducing defect density and growth method thereof

Abstract

The invention relates to the technical field of semiconductor materials, in particular to an epitaxial structure for reducing defect density and a growth method thereof. Comprising a sapphire substrate, and a buffer layer, a transition layer and a GaN epitaxial layer are sequentially arranged on the sapphire substrate. The buffer layer is composed of the InxB (1-x) N sub-layer and the InyAI (1-y) N sub-layer, component gradual change improves lattice mismatch between the village and the epitaxial layer, and stress between the village and the epitaxial layer is reduced. The transition layer is composed of the A1N transition layer 1 and the GazA1 (1-z) N transition layer 2, the pre-reaction and island nucleation density of AL can be effectively reduced by adopting a pulse periodic repetition change mode for the flow of AL, and subsequent improvement of the GaN film crystal quality is facilitated; the growth arrangement of the GazA1 (1-z) N transition layer 2 can effectively adjust the change of crystal lattices of the GazA1 (1-z) N transition layer 2, so that the GazA1 (1-z) N transition layer 2 plays a connecting role, and favorable conditions are created for the subsequent growth of the GaN film.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and particularly relates to an epitaxial structure for reducing defect density and a growth method thereof. Background Art

[0002] GaN materials are widely used in many research fields of nitride semiconductors such as LED light-emitting diodes and power electronic devices. Due to the high difficulty and cost of the GaN single crystal substrate manufacturing process, currently, the substrates used for epitaxial materials are mostly sapphire Al 2 O 3 , Si, and SiC; with the development of technology, especially the increasing requirements for the quality of epitaxial materials in the field of full-color displays, in recent years, Micro LED display has been considered by the industry as the ultimate display in the future. Therefore, Micro LED direct display has become the key layout direction of nitride semiconductor leading enterprises. Major domestic display manufacturers have all started to extend their layouts to GaN-based LED epitaxial chips. For example, BOE invested in Huacan Optoelectronics, Hisense invested in Qianzhao Optoelectronics, and Huaxing joined forces with Sanan Optoelectronics, etc.

[0003] LED epitaxial chip manufacturers mainly use sapphire substrates as the base. Usually, a buffer layer is first grown on the sapphire substrate, and the buffer layer is mostly composed of materials such as AlN, AlGaN, or GaN. Traditional growth methods, such as Figure 1 shown, the growth mode of sapphire substrate + buffer layer + GaN epitaxial layer has sparse island numbers, blurred boundaries, and disorderly directions, which will inevitably cause the subsequent GaN columnar crystals to have no consistent direction. During the island merging process, the shape (tilt, deviation, distortion) and quality of the islands will cause a large number of screw dislocations, edge dislocations, and mixed dislocations to appear in the GaN material. These line defects will extend through the entire GaN material during the subsequent growth process, resulting in a large number of line defects in the GaN thin film. After the chip is processed into an LED chip, there will be poor optoelectronic properties such as low quantum efficiency, serious leakage, and poor ESD resistance. Summary of the Invention

[0004] Aiming at the deficiencies of the prior art, the present invention provides an epitaxial structure for reducing defect density and a growth method thereof. A buffer layer is grown on a sapphire substrate, and the buffer layer is composed of two sub-layers of In x B (1-x) N and In y Al (1-y) N; a transition layer is grown on the buffer layer, and the transition layer is composed of an AlN transition layer 1 and Ga z Al (1-z)The N transition layer consists of two sub-layers; by gradually changing the composition of the buffer layer and the transition layer, the lattice mismatch between the substrate and the epitaxial layer is changed, the stress between the substrate and the epitaxial layer is reduced, the crystal quality of the McroLED green and blue epitaxial GaN material can be improved, the defect density can be reduced, thereby reducing leakage current and improving the quantum efficiency of the light-emitting diode.

[0005] To achieve the above object, the present invention adopts the following technical solutions: An epitaxial structure for reducing defect density, including a sapphire substrate, on which a buffer layer, a transition layer, and a GaN epitaxial layer are sequentially arranged. The buffer layer consists of In x B (1-x) N and In y Al (1-y) N two sub-layers; the transition layer consists of an A1N transition layer 1 and a Ga z A1 (1-z) N transition layer 2 two sub-layers.

[0006] Further, the GaN epitaxial layer sequentially includes an undoped GaN layer UGaN, an n-type semiconductor layer nGaN, a multi-quantum well (MQW) layer of an active layer InGaN, an electron blocking layer EBL, a p-type semiconductor layer pGaN, and a p-type GaN contact layer.

[0007] An epitaxial growth method for reducing defect density, including the following steps: Step 1: Provide a sapphire substrate; Step 2: Grow a buffer layer on the sapphire substrate; the buffer layer consists of In x B (1-x) N and In y Al (1-y) N two sub-layers. For the first sub-layer, the growth temperature is changed gradually, the temperature is set to gradually decrease from 1000 °C to 600 °C, the flow rate of material B decreases from a preset M to 0, and the flow rate of material In increases from 0 to N, so that the x value in In x B (1-x) N gradually changes from 0 to 1, and the concentration of B in the first sub-layer gradually decreases from bottom to top, while the concentration of In gradually increases, and the first sub-layer transitions from BN material to InN material; for the second sub-layer, the growth temperature is changed gradually, the temperature is set to gradually increase from 600 °C to 800 °C, the flow rate of material In decreases from a preset A to 0, and the flow rate of material AL increases from 0 to B, so that the y value in In y Al (1-y) N gradually changes from 1 (y < 1) to 0, and the concentration of In in the second sub-layer gradually decreases from bottom to top, while the concentration of A1 gradually increases, and the second sub-layer transitions from InAlN material to A1N material; Step 3: Grow a transition layer on the buffer layer; the transition layer consists of two sub-layers, i.e., AlN transition layer 1 and Ga z Al (1-z) N transition layer 2: AlN transition layer 1 adopts a cyclic structure with the number of cycles being 50 - 100; the growth temperature is grown in a constant temperature mode, and the temperature is set at 1200 °C; the flow rate of Al adopts a pulsed periodic repeated change mode, which changes in coordination with the cycle number period, and the initial value is 300 sccm; Ga z Al (1-z) N transition layer 2, the growth temperature is in a constant temperature mode, the temperature is set at 800 °C, the flow rate of the material Al gradually decreases from the preset C to 0, and the flow rate of the material Ga gradually increases from 0 to D, so that the z value in Ga z Al (1-z) N transition layer 2 gradually changes from 0 to 1, the concentration of Al in the transition layer 2 gradually decreases from bottom to top, and the concentration of Ga gradually increases, and the transition layer 2 transitions from AlN material to GaN material; Step 4: Grow an epitaxial layer on the transition layer.

[0008] Preferably, the thicknesses of the first sub-layer and the second sub-layer in Step 2 are both controlled between 30 nm and 50 nm; there is no H 2 introduced during the entire growth process of the two buffer sub-layers, the carrier gas is N 2 and the reaction gas is NH 3 , and the ratio of the three gases NH 3 :H 2 :N 2 is 1:0:2, and the growth pressure and rotation speed are constant, being 100 Torr and 1000 RPM respectively.

[0009] Preferably, there is no H 2 introduced during the entire growth process of AlN transition layer 1, the carrier gas is N 2 , the reaction gas is NH 3 , and the dosage ratio of NH 3 to N 2 is 1:3; the growth thickness of AlN transition layer 1 is controlled between 20 nm and 25 nm.

[0010] Preferably, the entire thickness of the Ga z Al (1-z) N transition layer 2 is controlled between 20 - 40 nm, and there is H z Al (1-z) introduced during the entire growth process of the Ga 2 Al 2 N transition layer, the carrier gas is N 3 , the reaction gas is NH 3:H 2 :N 2 is 1:1:2.

[0011] Compared with the prior art, the present invention has the following beneficial effects: The buffer layer of the present invention is composed of two sub-layers of InxB(1-x)N and InyAI(1-y)N. The gradual change of the composition improves the lattice mismatch between the substrate and the epitaxial layer and reduces the stress between the substrate and the epitaxial layer.

[0012] The transition layer of the present invention is composed of two sub-layers of A1N transition layer 1 and GazA1(1-z)N transition layer 2. The pulsed periodic repetition change mode of the AL flow rate can effectively reduce the pre-reaction of AL and the island nucleation density, which is beneficial to the improvement of the crystal quality of the subsequent GaN film; the growth setting of the GazA1(1-z)N transition layer 2 can effectively adjust the change of its lattice, playing a role of connecting the preceding with the following and creating favorable conditions for the growth of the subsequent GaN film. Description of the Drawings

[0013] Figure 1 is the prior epitaxial structure diagram.

[0014] Figure 2 is the epitaxial structure diagram of the present invention. Detailed Embodiments

[0015] To further elaborate on the technical means and effects adopted by the present invention to achieve the predetermined invention purpose, the following, in conjunction with the drawings and preferred embodiments, details the specific embodiments, structures, features and their effects of the present invention as follows.

[0016] As Figure 2 shown, an epitaxial structure for reducing the defect density of the present invention includes a sapphire substrate, a buffer layer is grown on the sapphire substrate, a transition layer is grown on the buffer layer, and an undoped GaN layer UGaN, an n-type semiconductor layer nGaN, a multi-quantum well (WQW) layer of an active layer InGaN, an electron blocking layer EBL, a p-type semiconductor layer pGaN, and a p-type GaN contact layer are sequentially grown on the transition layer.

[0017] The buffer layer is composed of In x B (1-x) N and In y Al (1-y) N two sub-layers: the growth temperature of the first sub-layer adopts a gradual change mode, the temperature is set to gradually decrease from 1000 °C to 600 °C, the flow rate of material B decreases from the preset M to 0, and the flow rate of material In increases from 0 to N, so that In x B (1-x)The value of x in N gradually increases from 0 to 1. The concentration of B in the first sublayer gradually decreases from bottom to top, and the concentration of In gradually increases. The first sublayer transitions from BN material to InN material; the growth temperature of the second sublayer adopts a gradient method, with the temperature set to gradually increase from 600 °C to 800 °C. The flow rate of material In gradually decreases from the preset A to 0, and the flow rate of material AL gradually increases from 0 to B, so that In y Al (1-y) The value of y in N gradually changes from 1 (y < 1) to 0. The concentration of In in the second sublayer gradually decreases from bottom to top, and the concentration of A1 gradually increases. The second sublayer transitions from InAlN material to A1N material; the thicknesses of both the first sublayer and the second sublayer are controlled between 30 nm and 50 nm; there is no H 2 introduced during the entire growth process of the two buffer sublayers, and the carrier gas is N 2 , and the reaction gas is NH 3 , and the ratio of the three gases NH 3 :H 2 :N 2 is 1:0:2, and the growth pressure and rotation speed remain constant, at 100 Torr and 1000 RPM respectively. Gradual change of the composition of the buffer layer can improve the lattice mismatch between the substrate and the epitaxial layer, reduce the stress between the substrate and the epitaxial layer, and is crucial for improving the number, shape (tilt, deviation, distortion) and quality of subsequent crystal islands.

[0018] The transition layer consists of two sublayers, A1N transition layer 1 and Ga z A1 (1-z) N transition layer 2: A1N transition layer 1 adopts a cyclic structure with the number of cycles being 50 - 100; the growth temperature adopts a constant temperature method, with the temperature set to 1200 °C; the flow rate of AL adopts a periodically repeated pulsed change method, which changes in coordination with the cycle number. The initial value is 300 sccm; there is no H introduced during the entire growth process of A1N transition layer 1 2 , and the carrier gas is N 2 , and the reaction gas is NH 3 , NH 3 usage ratio to N 2 usage ratio is 1:3; the growth thickness of A1N transition layer 1 is controlled between 20 nm and 25 nm. The periodically repeated pulsed change method of the flow rate of AL can effectively reduce the pre-reaction of AL and the island nucleation density, which is beneficial to the improvement of the crystal quality of the subsequent GaN film. Ga z A1 (1-z) N transition layer 2, the growth temperature adopts a constant temperature method, with the temperature set to 800 °C. The flow rate of material AL gradually decreases from the preset C to 0, and the flow rate of material Ga gradually increases from 0 to D, so that Ga z A1 (1-z)The z value in the N transition layer 2 gradually changes from 0 to 1. The concentration of Al in the transition layer 2 gradually decreases from bottom to top, and the concentration of Ga gradually increases. The transition layer 2 transitions from the A1N material to the GaN material, and the thickness of the entire layer is controlled at about 20 - 40 nm. z A1 (1-z) During the entire growth process of the N transition layer, H 2 is introduced, and the carrier gas is N 2 , and the reaction gas is NH 3 . The ratio of the three gases NH 3 :H 2 :N 2 is 1:1:2. z A1 (1-z) The growth setting of the N transition layer 2 can effectively adjust the change of its lattice, playing a role of connecting the preceding with the following, and creating favorable conditions for the growth of the subsequent GaN film.

[0019] The embodiments of the present disclosure utilize two lattice adjustment layers, namely the buffer layer and the transition layer, to achieve a gradual transition of the lattice, effectively reducing the stress between the sapphire substrate and the subsequent epitaxial layer, and providing a suitable substrate for improving the crystal quality of the subsequent GaN film and reducing the defect density. The lattice changes of the buffer layer and the transition layer effectively reduce the stress between the sapphire substrate and the epitaxial layer. After high-temperature annealing, regularly arranged island crystals can be obtained. The boundaries of the island crystals are clear and the density is moderate. During the subsequent island crystal merging process, the line defect density in the film layer can be significantly reduced, the crystal quality of the GaN film can be improved, the leakage current can be reduced, and thus the quantum efficiency of the light-emitting diode can be increased.

Claims

1. An epitaxial structure with reduced defect density, comprising a sapphire substrate, characterized in that: The sapphire substrate is provided with a buffer layer, a transition layer and a GaN epitaxial layer in sequence. The buffer layer is composed of In x B (1-x) N and In y Al (1-y) N two sublayers; the transition layer consists of A1N transition layer 1 and Ga z A1 (1-z) N transition layer 2 consists of two sublayers.

2. An epitaxial structure with reduced defect density as claimed in claim 1, characterized in that: The GaN epitaxial layer includes an undoped GaN layer UGaN, an n-type semiconductor layer nGaN, an active layer InGaN WQW layer, an electron blocking layer EBL, a p-type semiconductor layer pGaN, and a p-type GaN contact layer in sequence.

3. An epitaxial growth method for reducing defect density, characterized in that: The following steps are involved: Step 1: Providing a sapphire substrate; Step 2: Grow a buffer layer on the sapphire substrate; the buffer layer is composed of In x B (1-x) N and In y Al (1-y) N two sub-layers, the first sub-layer growth temperature is gradually reduced from 1000℃ to 600℃, the flow rate of material B is gradually reduced from the preset M to 0, and the flow rate of material In is gradually increased from 0 to N, so that In x B (1-x) The x value in N changes from 0 to 1. The concentration of B in the first sublayer decreases from bottom to top, and the concentration of In increases gradually. The first sublayer transitions from BN material to InN material. The growth temperature of the second sublayer is gradually increased from 600℃ to 800℃. The flow rate of material In decreases from the preset A to 0, and the flow rate of material AL increases from 0 to B, so that In y Al (1-y) The y value in N changes gradually from 1 to 0, y<1; the concentration of In in the second sublayer gradually decreases from bottom to top, and the concentration of A1 gradually increases, and the second sublayer transitions from InAlN material to A1N material; Step 3: Growth of transition layer on the buffer layer; the transition layer consists of A1N transition layer 1 and Ga z A1 (1-z) N transition layer 2 consists of two sublayers: A1N transition layer 1 adopts a cyclic structure with a cycle number of 50~100; the growth temperature is a constant temperature growth method with the temperature set to 1200℃; the flow rate of AL adopts a pulse periodic repetition change method with a cycle number periodic change, and the initial value is 300sccm; Ga z A1 (1-z) N transition layer 2, the growth temperature is constant, the temperature is set to 800℃, the flow rate of material AL is gradually reduced from the preset C to 0, and the flow rate of material Ga is gradually increased from 0 to D, so that Ga z A1 (1-z) The z value in the N transition layer 2 changes gradually from 0 to 1, the concentration of AL in the transition layer 2 decreases gradually from bottom to top, and the concentration of GA increases gradually, and the transition layer 2 transitions from A1N material to GaN material; Step 4: growing an epitaxial layer on the transition layer.

4. The epitaxial growth method for reducing defect density according to claim 3, characterized in that: In the step 2, the thickness of the first sublayer and the second sublayer are controlled between 30nm and 50nm; no H2 is introduced during the entire growth process of the two buffer sublayers, the carrier gas is N2, the reaction gas is NH3, the ratio of the three gases NH3:H2:N2 is 1:0:2, and the growth pressure and rotation speed are constant, which are 100Torr and 1000RPM respectively.

5. The epitaxial growth method for reducing defect density according to claim 4, characterized in that: In the step 3, H2 is not passed during the entire growth process of the AlN transition layer 1, the carrier gas is N2, the reaction gas is NH3, and the ratio of NH3 to N2 is 1:3; the growth thickness of the AlN transition layer 1 is controlled between 20nm and 25nm.

6. The epitaxial growth method for reducing defect density according to claim 5, characterized in that: In step 3, Ga z A1 (1-z) The thickness of N transition layer 2 is controlled at 20-40nm; Ga z A1 (1-z) H2 is introduced during the entire growth process of the N transition layer. The carrier gas is N2, the reaction gas is NH3, and the ratio of the three gases NH3:H2:N2 is 1:1:2.

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