GAN HEMT power device having adaptive charge regulation

Abstract

The present invention belongs to the technical field of power semiconductors, and relates to a GaN HEMT power device having adaptive charge regulation. In the present invention, a P-type GaN gate structure extending above a drift region is introduced, and a P-type GaN layer brought into contact with a gate electrode performs adaptive regulation on the charge distribution in the drift region, thereby achieving high voltage, low resistance and enhancement. In a turn-off state, a low-potential P-type GaN layer depletes two-dimensional electron gases (2DEGs), such that the 2DEGs in the drift region linearly increase from the gate electrode to a drain electrode, and a device obtains a uniform surface electric field and a high withstand voltage; during forward turn-on, a high-potential P-type GaN layer restores the 2DEGs below, and a turn-on resistance does not increase; and during dynamic switching, the uniform surface electric field alleviates a gate electron injection effect, and the capture of 2DEG channel electrons by a buffer layer trap is inhibited, thereby alleviating a current collapse effect. The present invention has the beneficial effects of: compared with a conventional GaN HEMT device, a higher withstand voltage being achieved without depreciating a turn-on resistance, a dynamic resistance collapse effect being inhibited, and no extra process step being added in the present invention.

Description

A GaN HEMT power device with adaptive charge regulation Technical Field

[0001] This invention belongs to the field of power semiconductor technology and relates to a GaN HEMT power device with adaptive charge regulation. Background Technology

[0002] GaN materials possess advantages such as wide bandgap and high critical breakdown electric field. Furthermore, due to the polarization effect, heterojunction high electron mobility transistors (HEMTs) can generate a high-concentration, high-mobility two-dimensional electron gas (2DEG) at the heterojunction interface. Compared to silicon-based devices, GaN-based power devices can achieve higher breakdown voltage and lower on-resistance, thus showing significant application potential in high-tech fields such as automotive electronics and aerospace. However, GaN HEMT devices are typically depletion-mode devices, leading to increased system power consumption and poor reliability. Moreover, their application faces the following problems: Firstly, the presence of electric field spikes, high defect and trap densities near the gate edge on the drain side increases leakage current, causing premature breakdown, with the breakdown voltage far below the theoretical limit of GaN materials. Secondly, the strong electric field between the gate (source) and drain can cause electrons to be injected into the interface states between the gate dielectric and the barrier layer, the surface states of the barrier layer between the gate and drain, and even the deep levels of the buffer layer under the 2DEG channel, leading to current collapse and dynamic resistance degradation. Currently, field plate technology is a common technique for improving breakdown voltage, but it is difficult to obtain a uniform surface electric field, thus limiting the improvement in breakdown voltage capability. JH Liu et al., in their paper "The Drift Region Width Modulation Technique for Breakdown Performance Enhancement of AlGaN / GaN HEMT," proposed a laterally variable width GaN HEMT. This technique uses etching to form a drift region with a width that linearly increases from the source to the drain, optimizing charge distribution, obtaining a uniform surface electric field, and improving device breakdown voltage. However, a 2DEG cannot be formed below the etched drift region, so the drift region charge homogenization technique often leads to a loss of conduction performance. Summary of the Invention

[0003] To address the aforementioned problems, this invention proposes a GaN HEMT power device with adaptive charge control.

[0004] The technical solution of this invention is as follows:

[0005] A GaN HEMT power device with adaptive charge regulation includes a substrate 1, a GaN buffer layer 2, a GaN channel layer 3, and an AlGaN barrier layer 4 stacked sequentially from bottom to top along the vertical direction of the device; along the lateral direction of the device, the device surface has a first conductive material 51, a gate structure, and a third conductive material 53 that do not contact each other from one side to the other, wherein the first conductive material 51 and the third conductive material 53 are respectively located at both ends of the upper surface of the AlGaN barrier layer 4, the source is led out from the upper surface of the first conductive material 51, and the drain is led out from the upper surface of the third conductive material 53;

[0006] The gate structure is characterized by comprising a second conductive material 52 and a P-type GaN layer 6, wherein the P-type GaN layer 6 is located on the upper surface of the barrier layer 4, and the second conductive material 52 is located on a portion of the upper surface of the P-type GaN layer 6. The P-type GaN layer 6 is divided into a first region and a second region depending on whether it is in contact with the second conductive material 52. The first region is in contact with the second conductive material 52 and forms a Schottky contact. The first region of the P-type GaN layer 6 is close to the first conductive material 51 and extends from one end of the device to the other along the longitudinal direction of the device. The second region of the P-type GaN layer 6 is close to the third conductive material 53 and extends along the longitudinal direction of the device. The two ends of the second region are defined as the first end and the second end, respectively. There is a gap between the first end and the device end, and the lateral width of the second region gradually increases from the first end to the second end. A gate is led out from the upper surface of the second conductive material 52. The longitudinal direction of the device is a direction perpendicular to the lateral direction of the device in a horizontal plane.

[0007] Furthermore, the lower ends of the first conductive material 51 and the third conductive material 53 extend into the barrier layer 4, forming an ohmic contact with the barrier layer 4.

[0008] Furthermore, the lower ends of the first conductive material 51 and the third conductive material 53 penetrate the barrier layer 4 and extend into the GaN channel layer 3, thereby forming an ohmic contact between the first conductive material 51 and the third conductive material 53 and the GaN channel layer 3.

[0009] Furthermore, the second region of the P-type GaN layer 6 has a shape that is one of stepped, triangular, and trapezoidal in the top view of the device. Beneficial effects

[0010] Introducing a P-type GaN gate structure extending above the drift region allows for adaptive control of the charge distribution in the drift region, achieving high voltage, low resistance, and enhancement mode. In the blocking state, the low-potential P-type GaN layer 6 depletes the two-dimensional electron gas (2DEG), resulting in a linear increase in the 2DEG from the gate to the drain in the drift region, providing a uniform surface electric field and high breakdown voltage. In the forward conduction state, the high-potential P-type GaN layer 6 restores the underlying 2DEG, without increasing the on-resistance. During dynamic switching, the uniform surface electric field alleviates the gate electron injection effect, suppresses the trapping of 2DEG channel electrons by the buffer layer traps, and mitigates current collapse. Simultaneously, the P-type GaN layer 6 provides recombination between holes and gate-injected electrons, shielding the gate electron injection from affecting the barrier layer and buffer layer, further suppressing dynamic resistance degradation. This invention is implemented through layout design, requiring no additional process steps. Attached Figure Description

[0011] Figure 1 is a structural schematic diagram of Embodiment 1 of the present invention;

[0012] Figure 2 is a cross-sectional view along AA' of Embodiment 1 of the present invention;

[0013] Figure 3 is a cross-sectional view along BB' of Embodiment 1 of the present invention;

[0014] Figure 4 is a structural schematic diagram of Embodiment 2 of the present invention;

[0015] Figure 5 is a cross-sectional view along AA' of Embodiment 2 of the present invention;

[0016] Figure 6 is a cross-sectional view along BB' of Embodiment 2 of the present invention;

[0017] Figure 7 is a schematic diagram comparing the two-dimensional electric field of the present invention and a conventional GaN device, wherein (a) is the two-dimensional electric field distribution of Embodiment 2 of the present invention; and (b) is the two-dimensional electric field distribution of a conventional GaN device.

[0018] Figure 8 is a current density distribution diagram when the device is turned on in Embodiment 2 of the present invention. Embodiments of the present invention

[0019] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings and embodiments: Example 1

[0020] As shown in Figure 1, the device comprises a substrate 1, a GaN buffer layer 2, a GaN channel layer 3, and an AlGaN barrier layer 4 stacked sequentially from bottom to top along the vertical direction of the device; along the lateral direction of the device, the device surface has a first conductive material 51, a gate structure, and a third conductive material 53 that do not contact each other sequentially from one side to the other; the first conductive material 51 extends into the barrier layer 4, the lower surface of the barrier layer 4 forms an ohmic contact, and the upper surface leads out the source; the third conductive material 53 extends into the barrier layer 4, the lower surface of the barrier layer 4 forms an ohmic contact, and the upper surface leads out the drain; the gate structure comprises a second conductive material 52 and a P-type GaN layer 6; the upper surface of the P-type GaN layer 6 is in partial contact with the second conductive material 52, and the lower surface is in contact with the barrier layer 4, and the width of the portion of the P-type GaN layer 6 not in contact with the second conductive material 52 decreases in a stepwise manner from the near gate side to the drain side. The lower surface of the second conductive material 52 is in contact with the P-type GaN layer 6, and the contact type is Schottky contact. The gate is led out from the upper surface of the second conductive material 52.

[0021] The working principle of this example is as follows:

[0022] The device in Example 1 incorporates a P-type GaN gate structure extending above the drift region, which can adaptively control the charge distribution in the drift region, achieving high voltage, low resistance, and enhancement mode. In the blocking state, the low-potential P-type GaN layer 6 depletes the 2DEG. The 2DEG only exists at the AlGaN / GaN interface below the P-type GaN layer 6. Therefore, the drift region 2DEG increases stepwise from the gate to the drain. New electric field peaks are introduced at the steps of the drift region P-type GaN layer to optimize the surface electric field distribution. The more steps there are, the higher the breakdown voltage of the device. In the forward conduction state, the 2DEG below the high-potential P-type GaN layer 6 is restored. The electron current flows to the drain through the 2DEG below the entire barrier region, and the on-resistance does not increase. During dynamic switching, the uniform surface electric field alleviates the gate electron injection effect, suppresses the trapping of electrons in the 2DEG channel by the buffer layer trap, alleviates the current collapse effect, and the recombination of holes provided by the P-type GaN layer 6 with gate-injected electrons shields the effect of gate electron injection on the barrier layer and buffer layer, further suppressing dynamic resistance degradation. Compared to conventional GaN HEMT devices, this embodiment has higher withstand voltage and suppresses current collapse without compromising on-resistance. Example 2

[0023] As shown in Figure 4, the difference between this example and Example 1 is that in this example, the width of the portion of the P-type GaN layer 6 that is not in contact with the second conductive material 52 decreases linearly from the near-gate side to the drain side in a GaN HEMT power device with adaptive charge control. Compared to Example 1, the advantage of this example is that a completely uniform surface electric field can be obtained in the blocking state, thereby further improving the breakdown voltage.

[0024] Figure 7 shows a comparison of the two-dimensional electric fields of Embodiment 2 of the present invention and conventional GaN devices. As can be seen from the figure, the conventional structure has a high electric field peak at the gate, which leads to premature breakdown and dynamic resistance degradation. The structure proposed in this invention can alleviate the electric field peak at the gate, and the AlGaN barrier layer obtains a more uniform electric field distribution, thus achieving a higher breakdown voltage. The uniform electric field distribution is beneficial to suppressing trapped electrons, thereby suppressing the current collapse effect.

[0025] Figure 8 shows the electron gas distribution in Embodiment 2 of the present invention when it is turned on. As can be seen from the figure, when the structure proposed in this invention is turned on, the 2DEG is restored, and the electron current can flow to the drain through the 2DEG below the entire barrier layer, so the on-resistance of the device does not increase.

Claims

1. A GaN HEMT power device with adaptive charge regulation, comprising, from bottom to top in the vertical direction of the device, a substrate (1), a GaN buffer layer (2), a GaN channel layer (3), and an AlGaN barrier layer (4); in the lateral direction of the device, the device surface has, from one side to the other, a first conductive material (51), a gate structure, and a third conductive material (53) that do not contact each other, wherein the first conductive material (51) and the third conductive material (53) are respectively located at both ends of the upper surface of the AlGaN barrier layer (4), the upper surface of the first conductive material (51) leads out a source electrode, and the upper surface of the third conductive material (53) leads out a drain electrode. characterized in that The gate structure comprises a second conductive material (52) and a P-type GaN layer (6), wherein the P-type GaN layer (6) is located on the upper surface of the barrier layer (4), and the second conductive material (52) is located on the upper surface of part of the P-type GaN layer (6); according to whether the P-type GaN layer (6) contacts the second conductive material (52), the P-type GaN layer (6) is divided into a first region and a second region, wherein the first region contacts the second conductive material (52) and forms a Schottky contact; the first region of the P-type GaN layer (6) is close to the first conductive material (51), and in the longitudinal direction of the device, the first region extends from one end of the device to the other end, while the second region of the P-type GaN layer (6) is close to the third conductive material (53), and in the longitudinal direction of the device, two ends of the second region are defined as a first end and a second end, respectively, wherein the first end has a spacing from the end of the device, and the lateral width of the second region gradually increases in the direction from the first end to the second end; the upper surface of the second conductive material (52) leads out a gate electrode; the longitudinal direction of the device is the direction perpendicular to the lateral direction of the device in the horizontal plane.

2. The GaN HEMT power device with adaptive charge regulation of claim 1, wherein, The lower end of the first conductive material (51) and the third conductive material (53) extends into the barrier layer (4) to form an ohmic contact with the barrier layer (4).

3. The GaN HEMT power device with adaptive charge regulation of claim 1, wherein, The lower end of the first conductive material (51) and the third conductive material (53) extends through the barrier layer (4) and into the GaN channel layer (3), so that the first conductive material (51) and the third conductive material (53) form an ohmic contact with the GaN channel layer (3).

4. The GaN HEMT power device with adaptive charge regulation of any of claims 1-3, wherein, The shape of the second region of the P-type GaN layer (6) in the top view of the device is one of a stepped shape, a triangular shape, and a trapezoidal shape.

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