Enhanced AlGaN / GaN HEMT device and preparation method thereof

Abstract

The invention provides an enhanced AlGaN / GaN HEMT (High Electron Mobility Transistor) device and a preparation method thereof. The enhanced AlGaN / GaN HEMT device can obtain relatively high threshold voltage; the threshold voltage can be accurately regulated and controlled by changing the In component in the InGaN linear gradient gate layer, and HEMT devices with different threshold voltages can be customized according to the application scene of the HEMT device. By introducing the P-GaN back barrier layer under the gate, the threshold voltage of the HEMT device and the withstand voltage of the HEMT device can be further improved, and the use scene of the HEMT device is expanded.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor devices and relates to an enhanced AlGaN / GaN HEMT device and a preparation method thereof. Background Art

[0002] Group III nitrides have excellent properties such as large bandgap, high electron saturation drift velocity, good thermal stability and chemical stability, and radiation resistance. Among them, heterojunctions such as AlGaN / GaN and InAlN / GaN have high-density, high-mobility two-dimensional electron gas (2DEG) at the heterojunction interface due to the spontaneous polarization and piezoelectric polarization effect of group III nitrides, which makes group III nitrides extremely suitable for high-frequency and high-power scenarios. However, since AlGaN / GaN heterojunctions naturally have high-concentration 2DEG when no gate voltage is applied, conventional high electron mobility transistors (HEMTs) based on AlGaN / GaN heterojunctions are in a normally-on state, that is, depletion-mode devices. However, for the application of power devices, for safety and energy-saving considerations, transistors are required to be in a normally-off state, that is, enhancement-mode devices.

[0003] At present, the commonly used schemes for realizing enhanced AlGaN / GaN HEMT devices are: groove gate structure, fluorine (F) ion implantation under the gate, and cascade structure P-GaN gate. In the commonly used voltage source power devices, the threshold voltage is very important. When the threshold voltage is small, mis-conduction is prone to occur when the power switch undergoes gate-source oscillation. P-GaN gate structure HEMT is a structure commonly used in the industry due to its large threshold voltage. Among them, the working principle of P-GaN gate structure HEMT device is: to achieve 2DEG depletion by raising the energy band of AlGaN / GaN under the gate through the P-GaN gate layer, and the threshold voltage is related to the doping concentration of the P-GaN gate layer, the composition and thickness of the AlGaN layer, and the residual donor concentration in the AlGaN layer and the GaN layer. Since the activation energy of the doped ion Mg in the P-GaN gate layer is high, it is difficult to obtain a higher hole concentration in the P-GaN gate layer, and the residual donors in the AlGaN layer and the GaN layer are also difficult to improve due to the limitations of the growth conditions. Therefore, reducing the composition and thickness of the AlGaN layer to increase the threshold voltage is a common method, but reducing the composition and thickness of the AlGaN layer will lead to an increase in the on-resistance of the device and a decrease in the saturation current, which will limit the performance of the enhanced AlGaN / GaN HEMT device. In addition, some researchers have introduced back barriers to increase the threshold voltage of HEMT devices, but the existence of back barriers will also reduce the saturation current of HEMT devices. How to regulate the threshold voltage of enhanced AlGaN / GaN HEMT devices is a difficult problem currently faced by the industry and scientific research community.

[0004] Therefore, it is necessary to provide an enhanced AlGaN / GaN HEMT device and a method for preparing the same. Summary of the invention

[0005] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide an enhancement mode AlGaN / GaN HEMT device and a preparation method thereof, so as to solve the problem that it is difficult to increase the threshold voltage of the enhancement mode AlGaN / GaN HEMT device in the prior art.

[0006] To achieve the above-mentioned object and other related objects, the present invention provides an enhanced AlGaN / GaN HEMT device, wherein the enhanced AlGaN / GaN HEMT device comprises:

[0007] substrate;

[0008] An epitaxial structure located on the substrate, the epitaxial structure comprising a GaN channel layer and an AlGaN barrier layer stacked from bottom to top;

[0009] A patterned InGaN linear gradient gate layer located on the epitaxial structure, wherein the InGaN linear gradient gate layer partially exposes the AlGaN barrier layer, and as the thickness of the InGaN linear gradient gate layer increases, the mole fraction of the In component increases linearly and gradually, and the mole fraction of the In component gradually changes in a range of 0 to 50%;

[0010] A gate electrode is located on the InGaN linear gradient gate layer.

[0011] Optionally, the epitaxial structure also includes a high-resistance GaN buffer layer located below the GaN channel layer and in contact with the GaN channel layer, and the high-resistance GaN buffer layer has a localized P-GaN back barrier layer, and the vertical projection of the InGaN linear gradient gate layer is located in the localized P-GaN back barrier layer.

[0012] Optionally, the width of the local P-GaN back barrier layer is equal to the gate width of the InGaN linear gradient gate layer, and the length of the local P-GaN back barrier layer is greater than or equal to the effective gate length of the InGaN linear gradient gate layer and less than the distance between the source and drain electrodes.

[0013] Optionally, the epitaxial structure further includes a nucleation layer located on the substrate, and the nucleation layer includes one or more of an AlN layer, a GaN layer and an AlGaN layer.

[0014] Optionally, the substrate includes a silicon carbide substrate, a silicon substrate, a sapphire substrate, an aluminum nitride substrate or a gallium nitride substrate; and the molar fraction of the Al component in the AlGaN barrier layer is in the range of 15 to 30%.

[0015] Optionally, the gate electrode includes a Ni / Au gate electrode; and further includes a source electrode and a drain electrode penetrating the AlGaN barrier layer and contacting the GaN channel layer.

[0016] The present invention also provides a method for preparing an enhanced AlGaN / GaN HEMT device, comprising the following steps:

[0017] providing a substrate;

[0018] forming an epitaxial structure on the substrate, wherein the epitaxial structure includes a GaN channel layer and an AlGaN barrier layer stacked from bottom to top;

[0019] Forming an InGaN linear gradient gate layer on the epitaxial structure, wherein as the thickness of the InGaN linear gradient gate layer increases, the mole fraction of the In component increases linearly and gradually, and the mole fraction of the In component gradually changes in a range of 0 to 50%;

[0020] Patterning the InGaN linear gradient gate layer to expose a portion of the AlGaN barrier layer;

[0021] A gate electrode is formed on the InGaN linear gradient gate layer.

[0022] Optionally, the epitaxial structure includes a high-resistance GaN buffer layer formed below the GaN channel layer and in contact with the GaN channel layer, and a local P-GaN back barrier layer is formed in the high-resistance GaN buffer layer, and the vertical projection of the patterned InGaN linear gradient gate layer is located in the local P-GaN back barrier layer.

[0023] Optionally, the method for forming the localized P-GaN back barrier layer includes:

[0024] Using photolithography, forming an ion implantation pattern window on the surface of the high-resistance GaN buffer layer;

[0025] Mg ion implantation and annealing process are performed, wherein the Mg ion implantation dose includes 1E14-1E16cm -2 The energy of Mg ion implantation includes 40 to 70 KeV, the annealing temperature includes 1100 to 1200° C., and the annealing time includes 10 to 20 min.

[0026] Optionally, the width of the formed local P-GaN back barrier layer is equal to the gate width of the InGaN linear gradient gate layer, and the length of the formed local P-GaN back barrier layer is greater than or equal to the effective gate length of the InGaN linear gradient gate layer and less than the distance between the source and drain electrodes.

[0027] As described above, the enhanced AlGaN / GaN HEMT device and the preparation method thereof of the present invention can obtain a higher threshold voltage; the threshold voltage can be precisely controlled by changing the In component in the InGaN linear gradient gate layer, and HEMT devices with different threshold voltages can be customized according to the application scenarios of the HEMT device; by introducing a P-GaN back barrier layer under the gate, the threshold voltage of the HEMT device and the withstand voltage of the HEMT device can be further improved, thereby expanding the application scenarios of the HEMT device. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Shown is a process flow chart for preparing an enhancement mode AlGaN / GaN HEMT device according to an embodiment of the present invention.

[0029] Figure 2 It is a schematic diagram of the structure of an enhancement mode AlGaN / GaN HEMT device in an embodiment of the present invention.

[0030] Figure 3 Shown is a comparison of threshold voltage curves of HEMT devices corresponding to InGaN linear gradient gate layers with different In composition gradients.

[0031] Figure 4 It is a schematic structural diagram of an enhancement mode AlGaN / GaN HEMT device with a P-GaN back barrier layer in an embodiment of the present invention.

[0032] Figure 5 Shown is a comparison of transfer curves of enhancement mode AlGaN / GaN HEMT devices with and without a P-GaN back barrier layer.

[0033] Component number description

[0034] 100 Substrate

[0035] 200 Nucleation layer

[0036] 300 High resistance GaN buffer layer

[0037] 400 GaN channel layer

[0038] 500 AlGaN barrier layer

[0039] 600 InGaN linear gradient gate layer

[0040] 700 Gate electrode

[0041] 801 Source electrode

[0042] 802 Drain electrode

[0043] 900 P-GaN back barrier layer DETAILED DESCRIPTION

[0044] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0045] For example, when describing the embodiments of the present invention in detail, for the sake of convenience, the cross-sectional view showing the device structure will not be partially enlarged according to the general scale, and the schematic view is only an example, which should not limit the scope of protection of the present invention. In addition, in actual production, the three-dimensional space dimensions of length, width and depth should be included.

[0046] For ease of description, spatial relational terms such as “under”, “below”, “below”, “below”, “over”, etc. may be used herein to describe the relationship of one element or feature shown in the drawings to other elements or features. It will be understood that these spatial relational terms are intended to include other orientations of the device in use or operation in addition to the orientation depicted in the drawings, and may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features are formed between the first and second features, so that the first and second features may not be in direct contact. In addition, when a layer is referred to as being “between” two layers, it may be the only layer between the two layers, or one or more intervening layers may also be present.

[0047] It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and therefore the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0048] like Figure 2 This embodiment provides an enhanced AlGaN / GaN HEMT device, which includes a substrate 100, an epitaxial structure, a patterned InGaN linear gradient gate layer 600 and a gate electrode 700.

[0049] The epitaxial structure is located on the substrate 100, and the epitaxial structure at least includes a GaN channel layer 400 and an AlGaN barrier layer 500 stacked from bottom to top; the patterned InGaN linear gradient gate layer 600 is located on the epitaxial structure to expose a portion of the AlGaN barrier layer 500, and as the thickness of the InGaN linear gradient gate layer 600 increases, the molar fraction of the In component increases linearly and gradually, such as Figure 2 The middle arrow points to the growth direction of the InGaN linear gradient gate layer 600 , and the mole fraction of the In component gradually changes in the range of 0 to 50%; the gate electrode 700 is located on the InGaN linear gradient gate layer 600 .

[0050] The enhanced AlGaN / GaN HEMT device of this embodiment forms the InGaN linear gradient gate layer 600 on the AlGaN barrier layer 500. Based on the principle of polarization doping, when the mole fraction of the In component in the InGaN linear gradient gate layer 600 increases linearly with the increase of the growth thickness, its polarization strength increases in a gradient, inducing three-dimensional hole gas in InGaN to form a P-type doping effect, so that the HEMT device can obtain a higher threshold voltage.

[0051] As an example, the substrate 100 may include a silicon carbide substrate, a silicon substrate, a sapphire substrate, an aluminum nitride substrate, or a gallium nitride substrate, etc., and the specific substrate may be selected according to needs.

[0052] As an example, Figure 2 The epitaxial structure may further include a nucleation layer 200 located on the substrate 100. The nucleation layer 200 may include one or more of an AlN layer, a GaN layer and an AlGaN layer. The thickness of the nucleation layer 200 may include 30nm to 100nm, such as 30nm, 50nm, 100nm, etc.

[0053] As an example, Figure 2 The epitaxial structure may further include a high-resistance GaN buffer layer 300 located below the GaN channel layer 400 and in contact with the GaN channel layer 400, so as to prepare a HEMT device with good anti-leakage performance through the high-resistance GaN buffer layer 300, wherein the doping ions of the high-resistance GaN buffer layer 300 may include one or a combination of Fe ions and C ions. The thickness of the high-resistance GaN buffer layer 300 may be 300nm to 2μm, such as 300nm, 800nm, 1μm, 2μm, etc.

[0054] As an example, the molar fraction of the Al component in the AlGaN barrier layer 500 may range from 15 to 30%, such as 15%, 20%, 22%, 25%, 30%, etc., and the thickness of the AlGaN barrier layer 500 may range from 15 nm to 18 nm, such as 15 nm, 16 nm, 18 nm, etc. The thickness of the GaN channel layer 400 may range from 100 to 300 nm, such as 100 nm, 200 nm, 300 nm, etc.

[0055] As an example, the gate electrode 700 may include a Ni / Au gate electrode, but is not limited thereto.

[0056] As an example, Figure 2 , further comprising a source electrode 801 and a drain electrode 802 penetrating the AlGaN barrier layer 500 and contacting the GaN channel layer 400 , and the materials of the source electrode 801 and the drain electrode 802 are not limited herein.

[0057] like Figure 3 Indicates the Figure 2 The HEMT device structure in FIG. 1 and the threshold voltage curve comparison diagram of the HEMT device corresponding to the InGaN linear gradient gate layer 600 with different In component gradients are shown. The three curves are respectively the threshold voltage curves of the HEMT device when the molar fraction of the In component increases from 0 to 0.1, the molar fraction of the In component increases from 0 to 0.15, and the molar fraction of the In component increases from 0 to 0.2. It can be seen that as the molar fraction of the In component increases, the threshold voltage of the HEMT device gradually increases. Among them, the threshold voltage can be greater than 10V, so that the threshold voltage of the HEMT device can be precisely controlled by changing the content of the In component in the InGaN linear gradient gate layer, so as to customize HEMT devices with different threshold voltages according to the application scenarios of the HEMT device.

[0058] Further, such as Figure 4 In order to further improve the breakdown voltage and threshold voltage of the enhanced AlGaN / GaN HEMT device, a local P-GaN back barrier layer 900 may be formed on the high-resistance GaN buffer layer 300, and the vertical projection of the InGaN linear gradient gate layer 600 is located in the local P-GaN back barrier layer 900, as shown in FIG. Figure 4 The middle dotted line indicates the vertical projection of the InGaN linear gradient gate layer 600 .

[0059] Among them, it is preferred that the width of the local P-GaN back barrier layer 900 is equal to the gate width of the InGaN linear gradient gate layer 600, and the length of the local P-GaN back barrier layer 900 is greater than or equal to the effective gate length of the InGaN linear gradient gate layer 600 and less than the distance between the source electrode 801 and the drain electrode 802.

[0060] Specifically, Figure 5 The figure shows a comparison of transfer curves corresponding to an existing enhanced AlGaN / GaN HEMT device with a P-GaN gate structure when the device has the P-GaN back barrier layer 900 and when the device does not have the P-GaN back barrier layer 900. When the device has the P-GaN back barrier layer 900, the threshold voltage of the HEMT device can be increased.

[0061] In HEMT devices, due to the electric field distribution, the effective gate length is greater than the physical gate length, that is, the effective gate length is 1.5 times the physical gate length. The electric field is concentrated in the area from the edge of the physical gate to the edge of the effective gate, which makes breakdown more likely to occur. Therefore, in this embodiment, the P-GaN back barrier layer 900 introduced into the high-resistance GaN buffer layer 300 below the InGaN linear gradient gate layer 600 preferably has a length greater than or equal to the effective gate length, and the P-GaN back barrier layer 900 is used to form a PN junction with the high-resistance GaN buffer layer 300 to provide a reverse electric field, thereby achieving the purpose of weakening the electric field at the gate edge, thereby improving the breakdown voltage of the HEMT device; at the same time, the presence of the P-GaN back barrier layer 900 in the high-resistance GaN buffer layer 300 can further raise the energy band at the AlGaN / GaN heterojunction, promote the depletion of the two-dimensional electron gas, and improve the turn-on voltage of the HEMT device; in addition, since the P-GaN back barrier layer 900 only affects the concentration of the two-dimensional electron gas under the gate, it has no effect on the two-dimensional electron gas in most of the channels between the source and the drain, thereby reducing the saturation current attenuation problem caused by the introduction of the P-GaN back barrier layer 900.

[0062] Therefore, by introducing the P-GaN back barrier layer 900 under the gate, the threshold voltage and the withstand voltage of the HEMT device can be further improved, thereby expanding the application scenarios of the HEMT device.

[0063] like Figure 1 This embodiment also provides a method for preparing an enhanced AlGaN / GaN HEMT device, comprising the following steps:

[0064] S1: providing a substrate;

[0065] S2: forming an epitaxial structure on the substrate, wherein the epitaxial structure includes a GaN channel layer and an AlGaN barrier layer stacked from bottom to top;

[0066] S3: forming an InGaN linear gradient gate layer on the epitaxial structure, wherein as the thickness of the InGaN linear gradient gate layer increases, the mole fraction of the In component increases linearly and gradually, and the mole fraction of the In component gradually changes in a range of 0 to 50%;

[0067] S4: patterning the InGaN linear gradient gate layer to expose a portion of the AlGaN barrier layer;

[0068] S5: forming a gate electrode on the InGaN linear gradient gate layer.

[0069] The preparation of the enhancement-mode AlGaN / GaN HEMT device mentioned above can refer to the preparation method, but is not limited thereto. The structure of the enhancement-mode AlGaN / GaN HEMT device will not be described in detail here.

[0070] For details, see Figure 1 and Figure 2 The nucleation layer 200, the high-resistance GaN buffer layer 300, the GaN channel layer 400 and the AlGaN barrier layer 500 can be epitaxially grown on the substrate 100 by metal organic chemical vapor deposition (MOCVD), and then the InGaN linear gradient gate layer 600 is grown by MOCVD, and the InGaN linear gradient gate layer 600 is patterned by photolithography and etching processes to expose the AlGaN barrier layer 500, and then the source electrode 801, the drain electrode 802 and the gate electrode 700 are prepared.

[0071] In order to improve the breakdown voltage and threshold voltage of the AlGaN / GaN HEMT device, the growth of the high-resistance GaN buffer layer 300 can be stopped, and the sample can be taken out from the MOCVD device. A graphic window is formed at the gate position of the HEMT device by photolithography. The width of the graphic window is equal to the gate width, and the length is preferably greater than or equal to the effective gate length of the InGaN linear gradient gate layer 600, that is, 1.5 times the physical gate length. Then, Mg ions are implanted by an ion implanter, and the implantation dose includes 1E14~1E16cm -2 The injection energy includes 40-70 KeV, and high temperature annealing is performed to restore lattice damage, the annealing temperature includes 1100-1200°C, and the annealing time includes 10-20 minutes. Then the sample is put back into the MOCVD device to grow the GaN channel layer 400, the AlGaN barrier layer 500, the InGaN linear gradient gate layer 600, the source electrode 801, the drain electrode 802 and the gate electrode 700.

[0072] In summary, the enhanced AlGaN / GaN HEMT device and the preparation method thereof of the present invention can obtain a higher threshold voltage; the threshold voltage can be precisely controlled by changing the In component in the InGaN linear gradient gate layer, and HEMT devices with different threshold voltages can be customized according to the application scenarios of the HEMT device; by introducing a P-GaN back barrier layer under the gate, the threshold voltage of the HEMT device and the withstand voltage of the HEMT device can be further improved, thereby expanding the application scenarios of the HEMT device.

[0073] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. An enhanced AlGaN / GaN HEMT device, characterized in that: The enhanced AlGaN / GaN HEMT device comprises: substrate; An epitaxial structure located on the substrate, the epitaxial structure comprising a GaN channel layer and an AlGaN barrier layer stacked from bottom to top; A patterned InGaN linear gradient gate layer located on the epitaxial structure, wherein the InGaN linear gradient gate layer partially exposes the AlGaN barrier layer, and as the thickness of the InGaN linear gradient gate layer increases, the mole fraction of the In component increases linearly and gradually, and the mole fraction of the In component gradually changes in a range of 0 to 50%; A gate electrode is located on the InGaN linear gradient gate layer.

2. The enhancement mode AlGaN / GaN HEMT device according to claim 1, characterized in that: The epitaxial structure also includes a high-resistance GaN buffer layer located below the GaN channel layer and in contact with the GaN channel layer, and the high-resistance GaN buffer layer has a local P-GaN back barrier layer, and the vertical projection of the InGaN linear gradient gate layer is located in the local P-GaN back barrier layer.

3. The enhancement mode AlGaN / GaN HEMT device according to claim 2, characterized in that: The width of the local P-GaN back barrier layer is equal to the gate width of the InGaN linear gradient gate layer, and the length of the local P-GaN back barrier layer is greater than or equal to the effective gate length of the InGaN linear gradient gate layer and less than the distance between the source and drain electrodes.

4. The enhancement mode AlGaN / GaN HEMT device according to claim 1, characterized in that: The epitaxial structure further includes a nucleation layer located on the substrate, and the nucleation layer includes one or more of an AlN layer, a GaN layer and an AlGaN layer.

5. The enhancement mode AlGaN / GaN HEMT device according to claim 1, characterized in that: The substrate includes a silicon carbide substrate, a silicon substrate, a sapphire substrate, an aluminum nitride substrate or a gallium nitride substrate; the molar fraction of the Al component in the AlGaN barrier layer is in the range of 15-30%.

6. The enhancement mode AlGaN / GaN HEMT device according to claim 1, characterized in that: The gate electrode includes a Ni / Au gate electrode; and further includes a source electrode and a drain electrode penetrating the AlGaN barrier layer and contacting the GaN channel layer.

7. A method for preparing an enhanced AlGaN / GaN HEMT device, characterized in that: The following steps are involved: providing a substrate; forming an epitaxial structure on the substrate, wherein the epitaxial structure includes a GaN channel layer and an AlGaN barrier layer stacked from bottom to top; Forming an InGaN linear gradient gate layer on the epitaxial structure, wherein as the thickness of the InGaN linear gradient gate layer increases, the mole fraction of the In component increases linearly and gradually, and the mole fraction of the In component gradually changes in a range of 0 to 50%; Patterning the InGaN linear gradient gate layer to expose a portion of the AlGaN barrier layer; A gate electrode is formed on the InGaN linear gradient gate layer.

8. The method for preparing an enhancement mode AlGaN / GaN HEMT device according to claim 7, characterized in that: The epitaxial structure also includes a high-resistance GaN buffer layer formed below the GaN channel layer and in contact with the GaN channel layer, and a local P-GaN back barrier layer is formed in the high-resistance GaN buffer layer, and the vertical projection of the patterned InGaN linear gradient gate layer is located in the local P-GaN back barrier layer.

9. The method for preparing an enhancement mode AlGaN / GaN HEMT device according to claim 8, characterized in that: The method for forming the localized P-GaN back barrier layer comprises: Forming an ion implantation pattern window on the surface of the high-resistance GaN buffer layer by photolithography; Mg ion implantation and annealing process are performed, wherein the Mg ion implantation dose includes 1E14-1E16cm -2 The energy of Mg ion implantation includes 40 to 70 KeV, the annealing temperature includes 1100 to 1200° C., and the annealing time includes 10 to 20 min.

10. The method for preparing an enhancement mode AlGaN / GaN HEMT device according to claim 8, characterized in that: The width of the formed local P-GaN back barrier layer is equal to the gate width of the InGaN linear gradient gate layer, and the length of the formed local P-GaN back barrier layer is greater than or equal to the effective gate length of the InGaN linear gradient gate layer and less than the distance between the source and drain electrodes.

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