Photoconductive semiconductor switch fabricated laterally alongside GaN-on-Si field-effect transistors

Abstract

1. An integrated circuit structure comprising: a substrate having an upper surface; a gallium nitride layer disposed on the upper surface of the substrate; and a photoconductive semiconductor switch disposed laterally alongside a transistor on the gallium nitride layer integrated into the integrated circuit structure, wherein regrown gallium nitride material is disposed on the photoconductive semiconductor switch and operably coupled to the wafer.

Description

[Background technology]

[0001] The present disclosure is directed to improved gallium nitride (GaN) integrated circuit technology, particularly to structures including both GaN photoconductive semiconductor switches (PCSS) and / or photoconductive switching transistors and GaN transistors, and associated integrated circuit structures.

[0002] Currently, on-chip GaN-on-Si high electron mobility transistor (HEMT) switches and RF devices are controlled by electrical signals and are limited by the design and fabrication constraints of traditional semiconductor devices. For example, switching speed is limited by the device geometry and on / off current ratio. Another example includes the breakdown voltage of the device. The breakdown voltage is the maximum voltage that the device can handle before it fails catastrophically. This voltage is determined by the breakdown of the HEMT semiconductor material and / or dielectric when the electric field peak at the drain side, which is a function of the applied drain bias and the distance from the gate to the drain, exceeds the breakdown field of the material. The maximum operating voltage of current state-of-the-art GaN HEMT switches, which operate in a safe operating region below the breakdown voltage, is about 650V. Photoconductive semiconductor switches (PCSS) and photoconductive switching transistors are different devices that offer high-voltage switching capabilities, ultrafast switching speeds, or fast energy pulses that are switched by light rather than a bias applied by a metal gate. This can lead to increased operating voltages compared to traditional GaN HEMT switches and RF devices.

[0003] Furthermore, existing GaN PCSS structures are standalone devices fabricated through non-planar lift-off based processes and connected to transistors, integrated circuits (ICs), and light sources (e.g., lasers and light emitting diodes) as part of a larger module, either by wire bonding or circuit board designs.

[0004] Required for maximum performance and functional density are compactly integrated photoconductive semiconductor switches and photoconductive switching transistors. Summary of the Invention

[0005] In accordance with the present disclosure, there is provided an integrated circuit structure including a substrate having an upper surface, a gallium nitride layer disposed on the upper surface of the substrate, the substrate and the gallium nitride layer comprising a wafer, and a photoconductive semiconductor switch disposed laterally alongside a transistor on the gallium nitride layer incorporated within the integrated circuit structure, wherein regrown gallium nitride material is disposed on the photoconductive semiconductor switch and operably coupled to the wafer.

[0006] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include that the substrate comprises at least one of a silicon material and a silicon carbide material.

[0007] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include that the transistor comprises a field effect transistor.

[0008] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include that the photoconductive semiconductor switch includes a first electrical contact and a second electrical contact disposed on the GaN layer.

[0009] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include that the photoconductive semiconductor switch includes an aluminum gallium nitride layer disposed on a gallium nitride-on-silicon wafer, with a first electrical contact and a second electrical contact disposed laterally away from the mesa on the gallium nitride layer of the wafer, and regrown gallium nitride material is deposited over each of the first electrical contact and the second electrical contact and disposed on the gallium nitride between the first electrical contact and the second electrical contact.

[0010] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include at least one of the regrown gallium nitride material and the gallium nitride layer forming a photoconductive circuit.

[0011] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include: the photoconductive semiconductor switch includes an aluminum gallium nitride layer disposed on a gallium nitride-on-silicon wafer; the first electrical contact and the second electrical contact are on a mesa disposed on the aluminum gallium nitride layer; an AlGaN-GaN two-dimensional electron-gas interface exists; windows are etched in the AlGaN layer; and a regrown GaN layer is deposited in the windows.

[0012] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include a regrown GaN layer disposed on the exposed gallium nitride layer at the window.

[0013] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include an integrated circuit structure further including a transparent silicon dioxide dielectric insulating layer configured to isolate the transistor from each of the first and second electrical contacts of the photoconductive semiconductor switch.

[0014] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include an integrated circuit structure further including a light source optically coupled to the photoconductive semiconductor switch.

[0015] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include the photoconductive semiconductor switch and the transistor each being configured to be utilized separately or interdependently.

[0016] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include a photoconductive semiconductor switch homogeneously integrated with a transistor on the gallium nitride-on-silicon wafer and configured to control the transistor.

[0017] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively further include the photoconductive semiconductor switch being homogeneously integrated with a transistor within the gallium nitride-on-silicon wafer and configured to be controlled by the transistor.

[0018] Further embodiments of any of the foregoing embodiments may additionally and / or alternatively include the dielectric and intermediate layers being transparent to a light source utilized to trigger the photoconductive semiconductor switch.

[0019] Further details of the GaN-on-Si heterogeneous technology are described in the following detailed description and the accompanying drawings, in which like reference numbers represent like elements. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic cross-sectional view of an exemplary lateral integrated circuit structure;

[0021] [Diagram 2] FIG. 1 is a schematic cross-sectional view of an exemplary GaN PCSS.

[0022] [Diagram 3] FIG. 1 is a schematic cross-sectional view of an exemplary GaN PCSS. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] Referring to FIG. 1, a lateral integrated circuit structure 10 is shown. The lateral integrated circuit structure 10 includes transistors 12 electrically coupled to a PCSS 14, each laterally integrated and supported on a common substrate 16. The transistors 12 may be FETs, such as GaN transistors, Si transistors, and associated integrated circuit structures. The PCSS 14 may include a GaN PCSS. The substrate 16 may include silicon (Si) or a silicon carbide material (SiC). The substrate 16 includes a top surface 18.

[0024] A gallium nitride (GaN) layer is disposed on top surface 18 of substrate 16 to form a GaN-on-Si wafer 22. GaN layer 20 supports transistor 12 and PCSS 14 in tandem such that transistor 12 and PCSS 14 are laterally integrated and incorporated into the same integrated circuit.

[0025] The FET 12 includes an aluminum gallium nitride (AlGaN) layer 24 disposed on the GaN layer 20. The FET 12 includes a silicon nitride dielectric (SiN / dielectric) layer 26 disposed on the AlGaN layer 24 adjacent to each of the drain D, gate G, and source S of the FET 12. A silicon dioxide dielectric (SiO2 / dielectric) layer 28 insulates the circuitry of the transistor 12 as well as an intermediate layer 30, here SiNx, and a conductive interconnect 31 disposed within the silicon dioxide dielectric layer 28. The dielectrics 28, 26, and intermediate layer 30 may be transparent to a light source 32 utilized to trigger the conductive path of the PCSS 14. In an exemplary embodiment, if the dielectric or intermediate layer is not transparent, a window may be provided in the film to allow light transmission.

[0026] The PCSS 14 may include a first electrical contact 34 (PCSS-1) and a second electrical contact 36 (PCSS-2) disposed on the GaN layer. In an exemplary embodiment, a silicon dioxide dielectric layer 28 insulates each of the first electrical contact 34 and the second electrical contact 36 of the photoconductive semiconductor switch 14. In an exemplary embodiment, the dielectric layer 28 may be a silicon nitride, or silicon dioxide material, or the like. In other exemplary embodiments, the first electrical contact 34 and the second electrical contact 36 do not have a dielectric insulation. The photoconductive semiconductor switch 14 is a region of a semiconductor material (such as GaN) that is normally very resistive, here unintentionally doped or doped with deep levels, such as carbon or iron, for example. This allows the material to block a significant amount of voltage with a very low leakage current. However, when illuminated with a light source 32 having an energy above or close to the band gap energy, a large amount of excited carriers are generated. These excited carriers form a low resistance conductive path used for switching. The PCSS 14 provides high voltage switching capability, very fast switching speed, or fast energy pulses. The input voltage to the transistor 12 can be controlled by the on / off state of the PCSS 14, or vice versa.

[0027] 2 and 3, the GaN PCSS 14 can be fabricated on the wafer 22 in a variety of ways.

[0028] 2, in an exemplary embodiment, PCSS 14 may include a substrate 16 having a GaN layer 20 disposed thereon that constitutes a wafer 22. A first electrical contact 34 and a second electrical contact 36 are disposed laterally on GaN layer 20 of wafer 22, away from the mesa. Regrown GaN material 40 is deposited over each of first electrical contact 34 and second electrical contact 36, and over gallium nitride layer 20 between first electrical contact 34 and second electrical contact 36, such that either the regrown GaN material 40 and / or GaN layer 20 form a photoconductive circuit 42.

[0029] As shown in FIG. 3, in an exemplary embodiment, PCSS 14 may include a substrate 16 having a GaN layer 20 disposed thereon, which constitutes wafer 22. A first electrical contact 34 and a second electrical contact 36 are on a mesa disposed on AlGaN layer 24 such that an AlGaN-GaN two-dimensional interface (2DEG interface) exists. AlGaN layer 24 may be etched to form a GaN window 38 in 2DEG layer 24. Regrown GaN 40 may be deposited in window 38 in place of a gate metal (not shown). Regrown GaN 40 is formed on the exposed GaN layer 20 in window 38 etched from AlGaN layer 24.

[0030] The present disclosure provides photoconductive semiconductor switches and photoconductive switching transistors integrated monolithically or via wafer-to-wafer bonding or die stacking with transistors and light sources. To achieve this, subtractive planar processing techniques are required.

[0031] Technical advantages of the present disclosure include the direct integration of optical gate switches with GaN-on-Si process flows, enabling the inherent high voltage capability and fast response times of optical gate switches.

[0032] Another technical advantage of the present disclosure includes a structure that includes a single chip / wafer that includes both GaN-on-Si transistor devices and GaN PCSS devices, where the final device has the functionality of the GaN transistor, the Si transistor, and the GaN PCSS utilized separately or interdependently.

[0033] Another technical advantage of the present disclosure includes a PCSS device that controls or is controlled by GaN+Si devices homogeneously integrated within the same wafer.

[0034] Another technical advantage of the present disclosure includes structures with multiple options of photoconductive materials, such as AlGaN / GaN based substrates with free-standing or bonded regrown AlGaN / GaN, or AlGaN / GaN 2DEG connected by narrow regions of photoconductive AlGaN / GaN material.

[0035] Another technical advantage of the present disclosure includes regrown AlGaN / GaN that can be configured and tuned independently of the epitaxial GaN in the substrate. Configuration and tuning parameters can include shape / thickness, doping, and concentration / stoichiometry.

[0036] Another technical advantage of the present disclosure includes that the method for fabricating GaN PCSS may be layer subtraction based using techniques traditional to Si foundries.

[0037] Another technical advantage of the present disclosure includes that both GaN PCSS transistors and GaN / Si transistors are fabricated simultaneously using the same processing steps.

[0038] Another technical advantage of the present disclosure includes the addition of PCSS to GaN-on-Si devices, which is a significant addition, because it utilizes layers and structures not used in standalone GaN-on-Si devices or standalone PCSS devices.

[0039] Another technical advantage of the present disclosure includes that, unlike GaN-on-Si devices, the 2DEG layer must be completely buried.

[0040] Another technical advantage of the present disclosure includes that, unlike typical PCSS devices, an AlGaN / GaN high electron mobility transistor (HEMPT) epi-substrate is used, as opposed to a bulk substrate optimized for photosensitivity.

[0041] A GaN-on-Si heterogeneous technology has been provided. Although the GaN-on-Si heterogeneous technology has been described in the context of specific embodiments thereof, other unforeseen alternatives, modifications, and variations will be apparent to those skilled in the art upon reading the foregoing description. It is therefore intended to cover such alternatives, modifications, and variations that fall within the broad scope of the appended claims.

Claims

1. 1. An integrated circuit structure comprising: a substrate having a top surface; a gallium nitride layer disposed on the top surface of the substrate, the substrate and the gallium nitride layer comprising a wafer; a photoconductive semiconductor switch disposed laterally alongside a transistor on the gallium nitride layer integrated within the integrated circuit structure; a regrown gallium nitride material is disposed on the photoconductive semiconductor switch and operably coupled to the wafer; Integrated circuit structure.

2. 10. The integrated circuit structure of claim 1, wherein the substrate comprises at least one of a silicon material and a silicon carbide material.

3. The integrated circuit structure of claim 1 , wherein the transistor comprises a field effect transistor.

4. 2. The integrated circuit structure of claim 1, wherein the photoconductive semiconductor switch comprises a first electrical contact and a second electrical contact disposed on the GaN layer.

5. 5. The integrated circuit structure of claim 4, wherein the photoconductive semiconductor switch comprises an aluminum gallium nitride layer disposed on a gallium nitride-on-silicon wafer, the first electrical contact and the second electrical contact are disposed laterally away from a mesa on the gallium nitride layer of the wafer, and the regrown gallium nitride material is deposited over each of the first electrical contact and the second electrical contact and is disposed on the gallium nitride between the first electrical contact and the second electrical contact.

6. 6. The integrated circuit structure of claim 5, wherein at least one of the regrown gallium nitride material and the gallium nitride layer forms a photoconductive circuit.

7. 5. The integrated circuit structure of claim 4, wherein the photoconductive semiconductor switch comprises an aluminum gallium nitride layer disposed on a gallium nitride-on-silicon wafer, the first electrical contact and the second electrical contact are on a mesa disposed on the aluminum gallium nitride layer, an AlGaN-GaN two-dimensional electron gas interface exists, a window is etched in the AlGaN layer, and a regrown GaN layer is deposited in the window.

8. 8. The integrated circuit structure of claim 7, wherein said regrown GaN layer is disposed on an exposed gallium nitride layer in said window.

9. 5. The integrated circuit structure of claim 4, further comprising a transparent silicon dioxide dielectric insulating layer configured to insulate each of the first and second electrical contacts of the photoconductive semiconductor switch from the transistor.

10. 10. The integrated circuit structure of claim 1 further comprising a light source optically coupled to said photoconductive semiconductor switch.

11. 10. The integrated circuit structure of claim 1, wherein said photoconductive semiconductor switch and said transistor are configured to be utilized separately or interdependently.

12. 2. The integrated circuit structure of claim 1, wherein the photoconductive semiconductor switch is homogeneously integrated with the transistor on a gallium nitride-on-silicon wafer and configured to control the transistor.

13. 2. The integrated circuit structure of claim 1, wherein said photoconductive semiconductor switch is homogeneously integrated with said transistor within a gallium nitride-on-silicon wafer and configured to be controlled by said transistor.

14. 10. The integrated circuit structure of claim 1, wherein the dielectric and intermediate layers are transparent to a light source utilized to trigger said photoconductive semiconductor switch.

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