High-stability GAN bidirectional device

Abstract

A high-stability GaN bidirectional device, comprising a substrate, and a transition layer, a buffer layer, a back-barrier layer, a channel layer, and barrier layer which are successively stacked on the substrate. A first gate (G1) and a second gate (G2) are respectively prepared on a first hole injection layer (P1) and a second hole injection layer (P2), and the first and second hole injection layers are located on the barrier layer; a first source (S1) and the second source (S2) are prepared on the barrier layer by means of an Ohmic contact, and are located on two sides of the first and second hole injection layers; the first source, the first hole injection layer, the second hole injection layer, and the second source are isolated from each other by passivation layers; and from the perspective of an energy band, the valence band maximum of the back-barrier layer is lower than the valence band maximum of the channel layer, thereby preventing hole injection into the substrate. The device has the functions of bidirectional conduction and bidirectional voltage withstanding, and can effectively suppress the current collapse effect caused by surface traps and substrate effects, enabling the device to have high dynamic stability and low dynamic on-resistance. The substrate can be connected to either source or left electrically floating to increase the breakdown voltage of the device.

Description

A highly stable GaN bidirectional device Technical Field

[0001] The present invention provides a GaN bidirectional device with high stability, belonging to the field of power electronic devices. Background Art

[0002] Devices composed of two GaN devices connected in series in reverse exhibit bidirectional voltage withstand and bidirectional conduction capabilities. Overlapping the drain terminals of the two GaN devices to form an integrated bidirectional device can reduce device area and lower on-resistance (Morita, Tatsuo, et al. "650 V 3.1 mΩcm 2 GaN-based monolithic bidirectional switch using normally-off gate injection transistor." 2007 IEEE International Electron Devices Meeting. IEEE, 2007). However, for integrated bidirectional devices on conventional GaN-on-Si epitaxial platforms, connecting the integrated device substrate to either source terminal or leaving the substrate floating results in negative charge accumulation in the buffer layer after the device experiences the high voltage withstand between the two sources in the off state, increasing the on-resistance of the device.

[0003] Currently, a technology has been proposed for actively switching the substrate connection position of a GaN bidirectional device based on its withstand voltage direction (Bahl, Sandeep R., et al. "Bi-directional gallium nitride switch with self-managed substrate bias." US Patent Application No. 13 / 922,352. No. 13 / 922,352). This technology increases circuit complexity by adding an additional control switch to switch the substrate connection. Summary of the Invention

[0004] To suppress dynamic resistance degradation caused by substrate effects and achieve high-stability, low-CCP GaN bidirectional devices, this paper proposes a novel GaN device structure that offers bidirectional conduction, bidirectional voltage resistance, and current-collapse suppression. Furthermore, the device features an electrically floating substrate, enhancing its voltage resistance.

[0005] The technical solutions of the present invention are as follows:

[0006] A GaN bidirectional device comprises a substrate and a transition layer, a buffer layer, a back barrier layer, a channel layer and a barrier layer stacked in sequence on the substrate; a first gate and a second gate are respectively formed on a first hole injection layer and a second hole injection layer, and the first hole injection layer and the second hole injection layer are located on the barrier layer; a first source and a second source are formed on the barrier layer using ohmic contacts, and are located on either side of the first hole injection layer and the second hole injection layer; the first source, the first hole injection layer, the second hole injection layer and the second source are isolated from each other by a passivation layer; from the perspective of energy bands, the valence band top of the back barrier layer is lower than the valence band top of the channel layer, thereby preventing holes from being injected into the substrate.

[0007] In the conventional GaN bidirectional device fabrication process, an additional back barrier layer is inserted between the channel layer and the buffer layer. This back barrier layer can be fabricated by MOCVD (metal-organic chemical vapor deposition) during epitaxial growth and has a thickness of 1-100 nm, preferably 15-25 nm. The back barrier layer can be made of one or more of aluminum gallium nitride, aluminum nitride, indium nitride, and aluminum indium gallium nitride.

[0008] As shown in Figure 2, the basic principle of the aforementioned GaN bidirectional device is demonstrated. When a positive bias is applied between the first gate G1 and the first source S1, or between the second gate G2 and the second source S2, the first hole injection layer P1 and the second hole injection layer P2 inject holes into the back barrier layer, where they are blocked. Simultaneously, the holes diffuse along the back barrier layer, forming a hole-conducting layer on the upper surface of the back barrier layer. This hole-conducting layer shields the negative charge in the buffer layer. Furthermore, this conductive layer shields the modulation of the two-dimensional electron gas by the substrate voltage, thereby suppressing the substrate effect.

[0009] In the aforementioned GaN bidirectional device, the substrate can be a silicon substrate, sapphire substrate, aluminum nitride substrate, silicon carbide substrate, or the like. The transition layer, used to balance lattice and stress mismatch during epitaxy, can be made of aluminum nitride, gallium nitride, or a mixture of the two. The buffer layer, a high-resistance layer, is used to reduce the device's off-state leakage current and increase its breakdown voltage. It can be made of carbon- or iron-doped aluminum nitride, gallium nitride, or a mixture of the two. The channel layer, made of gallium nitride, provides a conductive channel for the two-dimensional electron gas (2DEG). The barrier layer can be made of one or more of aluminum gallium nitride, aluminum nitride, indium nitride, and aluminum indium gallium nitride (AING), and can generate a 2DEG through polarization effects. The passivation layer can be made of at least one dielectric material selected from aluminum oxide (Al2O3), silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), hafnium oxide (HfO2), and the like. The first and second hole injection layers are made of P-type doped semiconductors, which can be one or more of gallium nitride, aluminum gallium nitride, aluminum nitride, indium nitride, etc., and have a thickness of 1-400 nm, preferably 70-120 nm.

[0010] Furthermore, the GaN bidirectional device adds a P-type doped semiconductor thin layer next to the first hole injection layer and / or the second hole injection layer. The material of the P-type doped semiconductor thin layer can be one or more of gallium nitride, aluminum gallium nitride, aluminum nitride, indium nitride, etc. The longitudinal cross-section of the P-type doped semiconductor thin layer can be a long strip, a trapezoid, etc. The thickness of the P-type doped semiconductor thin layer is 1-400 nm, preferably 10-40 nm, depending on different design requirements and preparation processes. When the device is turned on, the P-type doped semiconductor thin layer can also inject holes into the back barrier layer, thereby increasing the injection layer area for injecting holes. At the same time, the movable holes in the P-type doped semiconductor thin layer can also shield surface traps, reducing the current collapse effect formed by the surface traps repelling the channel two-dimensional electron gas.

[0011] Furthermore, in the GaN bidirectional device, the first gate and the first source (or the second gate and the second source) of the device are short-circuited by interconnecting metal or other means to form a GaN device with bidirectional voltage resistance and unidirectional conduction capability.

[0012] The substrates of all the above device structures can be connected to any source level; they can also be electrically floating to increase the device breakdown voltage.

[0013] Beneficial effects of the present invention:

[0014] The GaN bidirectional integrated device of the present invention can effectively suppress the current collapse effect caused by surface traps and substrate effects, so that the device has high dynamic stability and low dynamic on-resistance. At the same time, the substrate can be electrically floating, which can enhance the voltage resistance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG1 is a two-dimensional cross-sectional view of a first GaN bidirectional device structure proposed in Example 1 of the present invention;

[0016] FIG2 shows the basic principle of the device in Example 1;

[0017] 3 is a two-dimensional cross-sectional view of a second GaN bidirectional device structure proposed in Example 2 of the present invention;

[0018] FIG4 is a two-dimensional cross-sectional view of a third GaN bidirectional device structure proposed in Example 3 of the present invention;

[0019] 5 is a two-dimensional cross-sectional view of a fourth GaN bidirectional device structure proposed in Example 4 of the present invention;

[0020] FIG6 is a two-dimensional cross-sectional view of a fifth GaN bidirectional device structure proposed in Example 5 of the present invention;

[0021] 7 is a two-dimensional cross-sectional view of a sixth GaN bidirectional device structure proposed in Example 6 of the present invention;

[0022] In the figure, G1 and G2 are gates, S1 and S2 are sources, P1 and P2 are hole injection layers, and P3 and P4 are P-type semiconductor thin layers. DETAILED DESCRIPTION

[0023] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below through specific embodiments in conjunction with the accompanying drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and should not be understood as limiting the present invention.

[0024] Example 1: The first GaN bidirectional device structure in the present invention

[0025] As shown in Figure 1, the device structure includes a substrate, transition layer, buffer layer, back barrier layer, channel layer, and barrier layer, as well as the passivation layer and field plate structures required in traditional HEMT devices. Source electrodes S1 and S2 are fabricated on the left and right ends of gate electrodes G1 and G2, respectively, using ohmic contacts. Gate electrodes G1 and G2 are fabricated on hole injection layers P1 and P2, respectively, which are then fabricated on barrier layers. Based on current fabrication processes, hole injection layers P1 and P2 are made of p-type doped semiconductors such as gallium nitride, aluminum gallium nitride, aluminum nitride, or indium nitride. The substrate can be one or more of silicon, sapphire, aluminum nitride, or silicon carbide. The transition layer, used to balance lattice and stress mismatch during epitaxy, can be aluminum nitride, gallium nitride, or a mixture of the two. The buffer layer is a high-resistance layer that can be doped with carbon or iron and made of aluminum nitride, gallium nitride, or a mixture of the two. It is used to reduce the device's off-state leakage current and increase its breakdown voltage. The back barrier layer can be a mixture of at least one of aluminum gallium nitride, aluminum nitride, indium nitride, and aluminum indium gallium nitride. From an energy band perspective, the valence band top of the back barrier layer is lower than the valence band top of the channel layer. The channel layer provides a conductive channel for the two-dimensional electron gas and is made of gallium nitride. The barrier layer can be a mixture of at least one of aluminum gallium nitride, aluminum nitride, indium nitride, and aluminum indium gallium nitride, providing a two-dimensional electron gas through polarization effects. The passivation layer can be made of at least one of dielectric materials such as aluminum oxide (Al2O3), silicon dioxide (SiO2), silicon nitride (SiN), aluminum nitride (AlN), and hafnium oxide (HfO2). The isolation layer can be either etched isolation or implanted isolation, or a combination of the two. Implanted isolation can use elements such as fluorine, nitrogen, and boron.

[0026] When the device is turned on, the hole injection layers P1 and P2 inject holes into the back barrier layer, where they are blocked. Simultaneously, the holes diffuse along the back barrier layer, forming a hole-conducting layer on the upper surface of the back barrier layer, as shown in Figure 2. This hole-conducting layer shields the negative charge in the buffer layer. Furthermore, it also shields the substrate voltage from modulating the two-dimensional electron gas, thereby suppressing the substrate effect.

[0027] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

[0028] Example 2: The second GaN bidirectional device structure in the present invention

[0029] The second GaN bidirectional device prepared in this embodiment is shown in Figure 3. A P-type semiconductor thin layer P3 is added next to any hole injection layer P1 or P2, and the other structures are consistent with those in Example 1. The added P-type semiconductor thin layer increases the injection layer area for injecting holes into the back barrier layer when the device is turned on, further improving the device's ability to suppress substrate effects. At the same time, when the device is turned on, the movable holes in the P-type semiconductor thin layer P3 will shield the effect of the negative surface charge captured by the surface traps on the channel two-dimensional electron gas concentration, suppressing the current collapse effect caused by the surface traps, thereby achieving a more stable GaN bidirectional device.

[0030] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

[0031] Example 3: The third GaN bidirectional device structure in the present invention

[0032] The third GaN bidirectional device prepared in this embodiment is shown in Figure 4. Next to the two hole injection layers P1 and P2, a P-type semiconductor thin layer P3 and P4 are added, respectively. The other structures are consistent with those in Example 1. The added P-type semiconductor thin layer increases the injection layer area for injecting holes into the back barrier layer when the device is turned on, further improving the device's ability to suppress substrate effects. At the same time, when the device is turned on, the movable holes in P3 and P4 will shield the negative surface charges captured by surface traps from affecting the channel two-dimensional electron gas concentration, suppressing the current collapse effect caused by surface traps, thereby achieving a more stable GaN bidirectional device.

[0033] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

[0034] Example 4: The fourth GaN bidirectional device structure in the present invention

[0035] The fourth GaN bidirectional device fabricated in this embodiment is shown in Figure 5 . The gate G1 and source S1 (or gate G2 and source S2) of this GaN device are connected via interconnecting metal or other means, forming a GaN device with bidirectional voltage withstand and unidirectional conduction. The remaining structure and effects of this embodiment are consistent with those of the first embodiment. The interconnecting metal can be any conductive metal and is not the primary innovation of this invention.

[0036] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

[0037] Example 5: The fifth GaN bidirectional device structure in the present invention

[0038] The fifth GaN bidirectional device fabricated in this embodiment is shown in Figure 6 . The gate G1 and source S1 (or gate G2 and source S2) of this GaN device are connected via interconnecting metal or other means, forming a GaN device with bidirectional voltage withstand and unidirectional conduction. The remaining structure and effects of this embodiment are consistent with those of the second embodiment. The interconnecting metal can be any conductive metal and is not the primary innovation of this invention.

[0039] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

[0040] Example 6: The sixth GaN bidirectional device structure in the present invention

[0041] The sixth GaN bidirectional device fabricated in this embodiment is shown in Figure 7. The gate G1 and source S1 (or gate G2 and source S2) of this GaN device are connected via interconnecting metal or other means, forming a GaN device with bidirectional voltage withstand and unidirectional conduction. The remaining structure and effects of this embodiment are consistent with those of the third embodiment. The interconnecting metal can be any conductive metal and is not the primary innovation of this invention.

[0042] The device substrate can be connected to any source level; it can also be electrically floating to increase the device breakdown voltage.

Claims

1. A GaN bidirectional device, comprising a substrate and a transition layer, a buffer layer, a back barrier layer, a channel layer, and a barrier layer stacked in sequence on the substrate, wherein a first gate and a second gate are respectively prepared on a first hole injection layer and a second hole injection layer, and the first hole injection layer and the second hole injection layer are located on the barrier layer; a first source and a second source are prepared on the barrier layer using ohmic contacts, and are located on either side of the first hole injection layer and the second hole injection layer; the first source, the first hole injection layer, the second hole injection layer, and the second source are isolated from each other by a passivation layer; from the energy band perspective, the valence band top of the back barrier layer is lower than the valence band top of the channel layer, thereby blocking holes from being injected into the substrate.

2. The GaN bidirectional device according to claim 1, wherein: The back barrier layer is made of one or more materials selected from the group consisting of aluminum gallium nitride, aluminum nitride, indium nitride and aluminum indium gallium nitride.

3. The GaN bidirectional device according to claim 1, wherein: The substrate is a silicon substrate, a sapphire substrate, an aluminum nitride substrate or a silicon carbide substrate.

4. The GaN bidirectional device according to claim 1, wherein: The material of the transition layer is aluminum nitride and / or gallium nitride; the material of the buffer layer is carbon or iron-doped aluminum nitride and / or gallium nitride; the material of the channel layer is gallium nitride; the material of the barrier layer is selected from one or more of aluminum gallium nitride, aluminum nitride, indium nitride and aluminum indium gallium nitride; the first hole layer and the second hole injection layer use P-type doped semiconductors, selected from one or more of gallium nitride, aluminum gallium nitride, aluminum nitride and indium nitride.

5. The GaN bidirectional device according to claim 1, wherein: A P-type doped semiconductor thin layer is added beside the first hole injection layer and / or the second hole injection layer.

6. The GaN bidirectional device according to claim 5, wherein: The material of the P-type doped semiconductor thin layer is one or more of gallium nitride, aluminum gallium nitride, aluminum nitride, and indium nitride.

7. The GaN bidirectional device according to claim 1, wherein: The first gate and the first source are short-circuited, or the second gate and the second source are short-circuited.

8. The GaN bidirectional device according to claim 7, wherein: The first gate and the first source, or the second gate and the second source, are short-circuited by interconnecting metal.

9. The GaN bidirectional device according to claim 5, wherein: The first gate and the first source are short-circuited, or the second gate and the second source are short-circuited.

10. The GaN bidirectional device according to claim 9, wherein: The first gate and the first source, or the second gate and the second source, are short-circuited by interconnecting metal.

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