Gallium nitride heterojunction material structure and growth method thereof

Abstract

The invention discloses a gallium nitride heterojunction material structure and a growth method thereof, and relates to the technical field of semiconductor single crystal films, the material structure comprises a SiC substrate, an AlN nucleating layer, an AlGaN buffer layer, a GaN channel layer, an AlN insertion layer, a gradient component AlGaN barrier layer and a GaN cap layer from bottom to top; the material is prepared on a substrate in an epitaxial mode through a metal organic matter chemical vapor deposition method. AlGaN with gradually-changed Al components is adopted as the barrier layer, so that the electric field intensity of the barrier is reduced, the voltage endurance capability of the device is improved, and the power density and the reliability of the device are improved.

Description

Technical Field

[0001] The present application relates to the technical field of semiconductor single crystal thin films, and in particular to a gallium nitride heterojunction material structure and a growth method thereof. Background Art

[0002] AlGaN / GaN high electron mobility field effect transistor HEMT is a new type of semiconductor electronic device that produces a high concentration of two-dimensional electron gas at the heterojunction interface channel based on the unique polarization effect of nitride and controls the channel switch by gate voltage. It has high frequency, high power and high temperature resistance characteristics. This material system is more suitable for the development of high temperature, high voltage, high power microwave devices, and has broad application prospects in 5G mobile communications and other fields.

[0003] The AlGaN / GaN heterojunction belongs to a lattice mismatch system. There is a lattice mismatch between the AlGaN barrier layer and the GaN channel layer, which produces strong lattice strain and piezoelectric effect. That is, due to the existence of lattice stress, an electric field is generated in the crystal. Conversely, when the crystal is subjected to an electric field, lattice stress will also be generated, which is called the inverse piezoelectric effect. The electric field intensity near the gate edge in the AlGaN barrier layer is the highest, and the energy density of the stored elastic deformation is also the highest. Under high power and high temperature working conditions, excessive stress caused by the inverse piezoelectric effect produces lattice defects, which is also considered to be the main failure mechanism of AlGaN / GaN HEMT devices during high-voltage operation.

[0004] In the early current collapse research, Simin et al. proposed that under strong RF alternating voltage, the inverse piezoelectric effect will cause the AlGaN barrier layer to produce new strain and modulate the electron gas density in the channel, causing current collapse. However, quantitative analysis shows that the strain produced by the inverse piezoelectric effect is not large enough to explain the observed current collapse phenomenon. Joh et al. found from the experimental research on GaN HEMT that the device performance degradation mainly depends on the electric field in the device rather than the current. They believe that the strong electric field in the AlGaN barrier layer expands the lattice through the inverse piezoelectric effect, causing lattice relaxation and generating new lattice defects, which constitute electron traps. The higher the AlGaN barrier layer composition, the greater the AlGaN / GaN heterojunction mismatch, the greater the tensile stress generated in the barrier layer, the stronger the electric field in the barrier layer, and the more significant the inverse piezoelectric effect. Therefore, the AlGaN barrier layer must be optimized to reduce the peak electric field strength and elastic energy density in the barrier layer, so as to avoid the reliability problems of GaN high-voltage and high-power devices caused by the inverse piezoelectric effect.

[0005] There are three main types of graded AlGaN layers used in GaN HEMT structures. The first type is used as a buffer layer, or back barrier, to improve the channel electron mobility and the ability to limit the two-dimensional electron gas, reduce the device's buffer layer leakage, and improve the breakdown voltage and gate control ability. On the other hand, by using the aluminum component gradient of the high-resistance buffer layer aluminum gallium nitride, the lattice strain is reduced, the piezoelectric polarization is reduced, and the overall stability and reliability of the HEMT device are improved; the second type is the gradient AlGaN as the cap layer. The Al component gradient AlGaN layer produces a high concentration of holes, which depletes the two-dimensional electron device under the gate and realizes the enhancement-mode GaN-based HEMT device. The Al component gradient AlGaN layer has a larger bandgap width compared with P-type GaN, which can effectively improve the gate leakage, increase the breakdown voltage, and enhance the reliability of the device; the third type is the gradient AlGaN as the channel layer, using a double AlGaN gradient layer and a GaN layer to form a heterojunction. This structure enables the Al component gradient AlGaN layer and the GaN layer to form a three-dimensional electron gas, turning the gradient layer into a gradient channel, adjusting the distribution of the electric field, and improving the breakdown voltage and cutoff frequency of the device.

[0006] In the design of GaN HEMT material structure, most existing technologies use AlGaN back barrier to improve the voltage resistance characteristics of the buffer layer. In terms of heterojunction, GaN cap layer technology is mainly used to adjust the peak electric field at the gate edge close to the drain to improve the breakdown voltage of GaN HEMT devices.

[0007] There are also patents that use gradient AlGaN layers to improve the material's withstand voltage characteristics. For example, application number 2023117256654 discloses a groove gate GaN-based HEMT device and its preparation method. A groove gate structure is used to stack GaN layers, AlGaN layers with gradient Al composition, and metal gates from bottom to top. The local Al composition gradient AlGaN layer is used to generate a high concentration of holes, which depletes the two-dimensional electron gas under the gate to achieve an enhanced GaN-based HEMT device. Compared with P-type GaN, the Al composition gradient AlGaN layer has a larger bandgap width, which can effectively improve gate leakage, increase breakdown voltage, and improve device reliability.

[0008] The present application adopts graded composition AlGaN as the barrier layer, which not only avoids the complex groove gate process, but also overcomes the influence of the GaN cap layer structure on the channel carrier concentration, and reduces the mismatch stress of the AlGaN barrier layer, thereby achieving the effect of reducing the electric field strength near the gate edge in the AlGaN barrier layer and the inverse piezoelectric effect, thereby improving the breakdown voltage and reliability of high-power GaN microwave devices. Summary of the invention

[0009] Technical issues solved:

[0010] The technical problem to be solved by the present application is that the operating voltage of the GaN high-power microwave device is relatively high, and a relatively high electric field strength is formed near the gate edge in the AlGaN barrier layer. The higher the barrier component, the greater the electric field strength. Reducing the barrier component can reduce the electric field strength. However, the polarization effect of the AlGaN / GaN heterojunction is also reduced, causing the channel carrier concentration to decrease, resulting in a decrease in the power density of the GaN HEMT device, and the like. A gallium nitride heterojunction material structure and a growth method thereof are provided, so that the AlGaN / GaN heterojunction has a relatively high polarization effect, and at the same time, the mismatch stress of the heterojunction can be reduced, the electric field strength near the gate edge is reduced, the voltage resistance of the GaN microwave device is improved, and the reliability of the GaN high-voltage and high-power device is improved.

[0011] Technical solution:

[0012] A gallium nitride heterojunction material structure, which comprises, from bottom to top, a substrate, an AlN nucleation layer, an AlGaN buffer layer, a GaN channel layer, an AlN insertion layer, an AlGaN barrier layer and a GaN cap layer, wherein the AlN nucleation layer has a thickness of 10-100nm, the AlGaN buffer layer has a thickness of 500-2000nm, the GaN channel layer has a thickness of 50-300nm, the AlN insertion layer has a thickness of 0.5-2nm, the AlGaN barrier layer has a thickness of 10-30nm, and the GaN cap layer has a thickness of 1-4nm.

[0013] As a preferred technical solution of the present application: the substrate is a SiC substrate.

[0014] As a preferred technical solution of the present application: the Al component of the AlGaN buffer layer is 0.02-0.10.

[0015] As a preferred technical solution of the present application: the AlGaN barrier layer is a graded-component AlGaN barrier layer, in which the Al component gradually decreases from bottom to top.

[0016] As a preferred technical solution of the present application: the Al composition range of the gradient composition AlGaN barrier layer near the AlN insertion layer is 0.25-0.35, and the Al composition range of the gradient composition AlGaN barrier layer near the GaN cap layer is 0.05-0.15.

[0017] The present application also discloses a method for growing any of the above-mentioned gallium nitride heterojunction material structures, the steps of which are as follows:

[0018] Step 1. Select a substrate and place it in a reaction chamber of a metal organic chemical vapor deposition device;

[0019] Step 2. Raise the temperature of the reaction chamber to 1000-1200°C, introduce hydrogen, and bake the substrate for 5-10 minutes;

[0020] Step 3. Adjust the reaction chamber temperature to 1000-1200°C, set the reaction chamber pressure to 50-100 Torr, introduce ammonia and trimethylaluminum, and grow a 10-100 nm thick AlN nucleation layer;

[0021] Step 4. Adjust the reaction chamber temperature to 1000-1100°C, set the reaction chamber pressure to 75-150 Torr, introduce trimethyl gallium, and grow a 500-2000nm thick AlGaN buffer layer;

[0022] Step 5. Turn off trimethylaluminum, adjust the reaction chamber pressure to 100-300Torr, keep the reaction chamber temperature unchanged, and grow a 50-300nm thick GaN channel layer;

[0023] Step 6. Turn off trimethylgallium, adjust the reaction chamber temperature to 1000-1100°C, set the reaction chamber pressure to 50-150 Torr, introduce trimethylaluminum, and grow a 0.5-2nm thick AlN insertion layer;

[0024] Step 7. Introduce trimethylgallium, keep the temperature and pressure of the reaction chamber constant, and grow a 10-30nm thick AlGaN barrier layer;

[0025] Step 8. Turn off trimethylaluminum, keep the temperature and pressure of the reaction chamber unchanged, and grow a 1-4nm thick GaN cap layer;

[0026] Step 9. Turn off the ammonia and trimethylgallium, cool to room temperature, and take out the slice.

[0027] As a preferred technical solution of the present application: in step seven, the trimethylaluminum flow rate is set to decrease linearly, or the trimethylgallium flow rate is set to increase linearly, so that the Al / Ga atomic ratio decreases linearly, and an AlGaN barrier layer with a gradually decreasing composition from bottom to top is grown.

[0028] Beneficial effects:

[0029] The gallium nitride heterojunction material structure and the growth method thereof described in the present application adopt the above technical solution and have the following technical effects compared with the prior art:

[0030] 1. A gallium nitride heterojunction material structure designed by the present invention uses graded composition AlGaN as a barrier layer to form an AlGaN / GaN heterojunction; the Al component is higher at one end close to the GaN channel layer, thereby forming a higher concentration of two-dimensional electron gas in the channel; the Al component is lower at one end close to the GaN cap layer, thereby reducing the mismatch stress of the AlGaN barrier layer, reducing the electric field strength near the gate edge in the AlGaN barrier layer and the inverse piezoelectric effect, and improving the withstand voltage capability and reliability of high-power GaN microwave devices;

[0031] 2. The AlGaN / AlN / GaN / AlGaN double heterojunction disclosed in the present application uses AlGaN with a gradient composition as a barrier layer, and the barrier composition gradually decreases from bottom to top. Experimental results show that this structural material can improve the device breakdown voltage and has a simple process;

[0032] 3. This application designs a gradient composition AlGaN / AlN / GaN / AlGaN double heterostructure material, which not only improves the channel carrier transport characteristics, but also increases the device breakdown voltage, and is particularly suitable for high-voltage and high-power device applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A schematic diagram of the structure of the gallium nitride heterojunction material of the present application;

[0034] Figure 2 This is a flow chart for preparing gallium nitride heterojunction materials for this application;

[0035] Figure 3 This is a comparison diagram of the energy bands and two-dimensional electron gas distribution diagrams of the gallium nitride heterojunction material of Example 1 of the present application, the material of Comparative Example 1, and the material of Comparative Example 2;

[0036] Figure 4 This is an electric field distribution diagram near the gate drain side of the gallium nitride heterojunction material under high voltage in Example 1 of the present application;

[0037] Figure 5 This is the electric field distribution diagram near the gate drain side of the material of Comparative Example 1 under high voltage;

[0038] Figure 6 This is the electric field distribution diagram near the gate drain side of the material of Comparative Example 2 under high voltage;

[0039] Figure 7 This is a comparison chart of the breakdown characteristics of the gallium nitride heterojunction material of Example 1 of the present application, the material of Comparative Example 1, and the material of Comparative Example 2.

[0040] Explanation of the reference numerals: 1. substrate, 2. AlN nucleation layer, 3. AlGaN buffer layer, 4. GaN channel layer, 5. AlN insertion layer, 6. AlGaN barrier layer, 7. GaN cap layer. DETAILED DESCRIPTION

[0041] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0042] A gallium nitride heterojunction material structure, such as Figure 1 As shown, its structure includes:

[0043] Substrate 1, the substrate material is SiC;

[0044] An AlN nucleation layer 2 is grown on the substrate 1 to wet the substrate 1, provide nucleation points for the subsequent buffer layer, and adjust the stress between the substrate 1 and the epitaxial layer;

[0045] The AlGaN buffer layer 3 is grown on the AlN nucleation layer 2 to release the lattice mismatch between the epitaxial layer and the substrate 1. At the same time, the bandgap of AlGaN is greater than that of the GaN buffer layer, and has a higher resistivity, which can improve the withstand voltage of the buffer layer. The Al component of the AlGaN buffer layer 3 is 0.02-0.10.

[0046] A GaN channel layer 4, which is grown on the AlGaN buffer layer 3, has a low defect density and provides a high-quality template for heterojunction growth;

[0047] An AlN insertion layer 5, which is grown on the GaN channel layer 4, can enhance the shielding effect and polarization effect of the channel quantum well, reduce alloy disorder scattering, and improve the concentration and mobility of the heterojunction two-dimensional electron gas;

[0048] An AlGaN barrier layer 6 is grown on the AlN insertion layer 5, forms a quantum well with the GaN channel layer 4, and generates a high-concentration two-dimensional electron gas through a polarization effect; the AlGaN barrier layer (6) is a graded component AlGaN barrier layer, in which the Al component gradually decreases from bottom to top. The Al component of the graded component AlGaN barrier layer near the AlN insertion layer 5 is in the range of 0.25-0.35, and the Al component of the graded component AlGaN barrier layer near the GaN cap layer (7) is in the range of 0.05-0.15.

[0049] The GaN cap layer 7 is grown on the AlGaN barrier layer 6, which can increase the barrier height of the AlGaN barrier layer and reduce device leakage.

[0050] The thickness of the AlN nucleation layer 2 is 10-100 nm, the thickness of the AlGaN buffer layer 3 is 500-2000 nm, the thickness of the GaN channel layer 4 is 50-300 nm, the thickness of the AlN insertion layer 5 is 0.5-2 nm, the thickness of the AlGaN barrier layer 6 is 10-30 nm, and the thickness of the GaN cap layer 7 is 1-4 nm.

[0051] The AlGaN mentioned in this application is a combination of AlN and GaN, and the sum of the number of atoms of the two group III elements in the alloy is equal to the number of atoms of the group V element. The ratio of the number of atoms of each group III element to the total number of atoms of the group III element is the composition of the group III element. If the Al composition is x and the Ga composition is y, then x+y=1.

[0052] Figure 2 is the preparation flow chart of the present invention, combined with Figure 1 Schematic diagram, the epitaxial growth method of the above-mentioned gallium nitride heterojunction material, the equipment used is MOCVD, wherein the V group source used is ammonia, the III group source used is trimethylgallium, trimethylaluminum, and the carrier gas is hydrogen or nitrogen. According to experimental research, the preferred preparation process and steps are obtained as described in the following embodiment.

[0053] Embodiment 1:

[0054] A method for growing a gallium nitride heterojunction material structure, comprising the following steps:

[0055] Step 1. Select substrate 1 and place it in the reaction chamber of MOCVD equipment;

[0056] Step 2. The reaction chamber is heated to 1050°C, the growth pressure is 100Torr, and the substrate 1 is baked in a hydrogen atmosphere for 10 minutes;

[0057] Step 3. Adjust the temperature of the reaction chamber, introduce ammonia and trimethylaluminum, and grow a 50 nm thick AlN nucleation layer 2 at a growth temperature of 1100°C and a growth pressure of 100 Torr;

[0058] Step 4. Introduce trimethylgallium, adjust the temperature and pressure of the reaction chamber, and grow an AlGaN buffer layer 3 with a thickness of 2000nm at a growth temperature of 1050°C and a growth pressure of 100Torr, wherein the Al component is 0.05;

[0059] Step 5. Turn off trimethylaluminum, adjust the temperature and pressure of the reaction chamber, and grow a GaN channel layer 4 with a thickness of 100 nm at a growth temperature of 1050° C. and a growth pressure of 200 Torr;

[0060] Step 6. Turn off trimethylgallium, turn on trimethylaluminum, adjust the pressure of the reaction chamber, and grow an AlN insertion layer 5 with a thickness of 1 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr;

[0061] Step 7. Turn on trimethylgallium, set the starting flow rate and ending flow rate of trimethylaluminum respectively, and grow an AlGaN barrier layer 6 with a thickness of 20 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr, wherein the Al component gradually changes from 0.3 at the beginning to 0.1 at the end;

[0062] Step 8. Turn off trimethyl aluminum, and grow a GaN cap layer 7 with a thickness of 2 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr;

[0063] Step 9. Turn off the ammonia and trimethylgallium, cool to room temperature, and take out the slice.

[0064] Embodiment 2:

[0065] A method for growing a gallium nitride heterojunction material structure, comprising the following steps:

[0066] Step 1. Select substrate 1 and place it in the reaction chamber of MOCVD equipment;

[0067] Step 2. The reaction chamber is heated to 1050°C, the growth pressure is 100Torr, and the substrate 1 is baked in a hydrogen atmosphere for 10 minutes;

[0068] Step 3. Adjust the temperature of the reaction chamber, introduce ammonia and trimethylaluminum, and grow an AlN nucleation layer 2 with a thickness of 100 nm at a growth temperature of 1100° C. and a growth pressure of 100 Torr;

[0069] Step 4. Introduce trimethylgallium, adjust the temperature and pressure of the reaction chamber, and grow an AlGaN buffer layer 3 with a thickness of 500 nm at a growth temperature of 1050°C and a growth pressure of 100 Torr, wherein the Al component is 0.1;

[0070] Step 5. Turn off trimethylaluminum, adjust the temperature and pressure of the reaction chamber, and grow a GaN channel layer 4 with a thickness of 200 nm at a growth temperature of 1050° C. and a growth pressure of 200 Torr;

[0071] Step 6. Turn off trimethylgallium, turn on trimethylaluminum, adjust the pressure of the reaction chamber, and grow an AlN insertion layer 5 with a thickness of 1 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr;

[0072] Step 7. Turn on trimethylgallium, set the starting flow rate and ending flow rate of trimethylaluminum respectively, and grow an AlGaN barrier layer 6 with a thickness of 20 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr, wherein the Al component gradually changes from 0.35 at the beginning to 0.05 at the end;

[0073] Step 8. Turn off trimethyl aluminum, and grow a GaN cap layer 7 with a thickness of 2 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr;

[0074] Step 9. Turn off the ammonia and trimethylgallium, cool to room temperature, and take out the slice.

[0075] Comparative Example 1:

[0076] A method for growing a gallium nitride heterojunction material structure is the same as that of Example 1, except that:

[0077] Step 7. Turn on trimethylgallium, set the flow rate of trimethylaluminum, and grow an AlGaN barrier layer 6 with a thickness of 20 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr, wherein the Al component is 0.2.

[0078] Comparative Example 2:

[0079] A method for growing a gallium nitride heterojunction material structure is the same as that of Example 1, except that:

[0080] Step 7. Turn on trimethylgallium, set the starting flow rate and ending flow rate of trimethylaluminum respectively, and grow an AlGaN barrier layer 6 with a thickness of 20 nm at a growth temperature of 1050° C. and a growth pressure of 100 Torr, wherein the Al component gradually changes from 0.1 at the beginning to 0.3 at the end.

[0081] The properties of the heterojunction materials grown by the three epitaxial material structures and processes of Example 1, Comparative Example 1 and Comparative Example 2 are shown in the following table. From the results, it can be seen that the material of the present invention adopting the bottom-up component gradient barrier structure has a higher two-dimensional electron gas concentration and mobility, and the device breakdown voltage based on the structural material is about 18% higher than that of the conventional structure, which has obvious advantages in the application of high-voltage and high-power devices.

[0082]

[0083] Figure 3-Figure 5 StrA is the material structure of the present invention, and its barrier component is 0.3 near the channel and 0.1 near the cap layer; Str B is comparative structure 1, and its barrier component is constant at 0.2; Str C is comparative structure 2, and its barrier component is 0.1 near the channel and 0.3 near the cap layer.

[0084] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. There are many practical production methods that can be adopted. All equivalent changes and decorations made according to the claims of the present invention are within the scope of the present invention.

Claims

1. A gallium nitride heterojunction material structure, characterized in that: The gallium nitride heterojunction material structure comprises, from bottom to top, a substrate (1), an AlN nucleation layer (2), an AlGaN buffer layer (3), a GaN channel layer (4), an AlN insertion layer (5), an AlGaN barrier layer (6) and a GaN cap layer (7), wherein the AlN nucleation layer (2) has a thickness of 10-100 nm, the AlGaN buffer layer (3) has a thickness of 500-2000 nm, the GaN channel layer (4) has a thickness of 50-300 nm, the AlN insertion layer (5) has a thickness of 0.5-2 nm, the AlGaN barrier layer (6) has a thickness of 10-30 nm, and the GaN cap layer (7) has a thickness of 1-4 nm.

2. The gallium nitride heterojunction material structure according to claim 1, characterized in that: The substrate (1) is a SiC substrate.

3. The gallium nitride heterojunction material structure according to claim 1, characterized in that: The Al component of the AlGaN buffer layer (3) is 0.02-0.

10.

4. The gallium nitride heterojunction material structure according to claim 1, characterized in that: The AlGaN barrier layer (6) is a graded-component AlGaN barrier layer, in which the Al component decreases gradually from bottom to top.

5. The gallium nitride heterojunction material structure according to claim 4, characterized in that: The Al composition of the graded composition AlGaN barrier layer is in the range of 0.25-0.35 near the AlN insertion layer (5), and in the range of 0.05-0.15 near the GaN cap layer (7).

6. A method for growing a gallium nitride heterojunction material structure according to any one of claims 1 to 5, characterized in that: Here are the steps: Step 1. Select a substrate (1) and place it in a reaction chamber of a metal organic chemical vapor deposition device; Step 2. The reaction chamber is heated to 1000-1200°C, hydrogen is introduced, and the substrate (1) is baked for 5-10 minutes; Step 3. Adjust the reaction chamber temperature to 1000-1200°C, set the reaction chamber pressure to 50-100 Torr, introduce ammonia and trimethylaluminum, and grow a 10-100 nm thick AlN nucleation layer (2); Step 4. Adjust the reaction chamber temperature to 1000-1100°C, set the reaction chamber pressure to 75-150Torr, introduce trimethylgallium, and grow a 500-2000nm thick AlGaN buffer layer (3); Step 5. Turn off trimethylaluminum, adjust the reaction chamber pressure to 100-300 Torr, keep the reaction chamber temperature unchanged, and grow a 50-300 nm thick GaN channel layer (4); Step 6. Turn off trimethylgallium, adjust the reaction chamber temperature to 1000-1100°C, set the reaction chamber pressure to 50-150 Torr, introduce trimethylaluminum, and grow a 0.5-2 nm thick AlN insertion layer (5); Step 7. Introduce trimethylgallium, keep the temperature and pressure of the reaction chamber constant, and grow a 10-30 nm thick AlGaN barrier layer (6); Step 8. Turn off trimethylaluminum, keep the temperature and pressure of the reaction chamber unchanged, and grow a 1-4 nm thick GaN cap layer (7); Step 9. Turn off the ammonia and trimethylgallium, cool to room temperature, and take out the slice.

7. The method for growing a gallium nitride heterojunction material structure according to claim 6, characterized in that: In the step 7, the flow rate of trimethylaluminum is set to decrease linearly, or the flow rate of trimethylgallium is set to increase linearly, so that the Al / Ga atomic ratio decreases linearly, and an AlGaN barrier layer (6) with a gradually decreasing composition from bottom to top is grown.

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