A photoconductive switch device having a waveguide structure

Abstract

The application discloses a photoconductive switch device with a waveguide structure, belonging to the field of power semiconductors, comprising: a dark-state high-resistance light-sensitive substrate, which simultaneously serves as a functional area of a photoconductor and a core layer of a light waveguide; a high-reflection front electrode and a high-reflection back electrode formed above and below the substrate; a side surface reflection-increasing film formed on the sidewall of the substrate; and a waveguide coupling window arranged on the substrate, which is used for coupling light emitted by a trigger light source into the substrate at an angle greater than the critical angle of total reflection of the substrate material, so that the light beam is conducted laterally in the substrate. The application greatly prolongs the effective optical path of the photoconductive switch device for non-intrinsic wavelengths, ensures sufficient absorption of incident light, effectively improves the light responsivity and photocurrent of the device, reduces the on-resistance, solves the problem of optical-electric field mismatch caused by light blocking of the electrode metal of a traditional photoconductive device, and simultaneously separates the light incidence area from the electrode area, thereby avoiding the problem of electric field concentration caused by the optical surface microstructure and being beneficial to improving the blocking capacity of the device.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of power semiconductors, and in particular to a photoconductive switch device with waveguide structure. BACKGROUND

[0002] The photoconductive switch device (PCSS) is based on the photoconductivity of semiconductor materials, with high-power lasers, LEDs as trigger light source, and a high-voltage DC bias is always applied during device operation. The device is turned on and off by triggering the light source, and can produce a pulse current of about 1000 A in an instant. It has the characteristics of fast response, good stability, and anti-electromagnetic interference, and is widely used in nuclear fusion ignition devices, electromagnetic launching devices, pulse electric field devices, and high-voltage DC circuit breakers. The PCSS requires the selected semiconductor material to adapt to the working environment of high voltage, high frequency, and large current. Wide-bandgap semiconductors such as vanadium-doped SiC and nitrogen-doped diamond have high breakdown field, high thermal conductivity, high electron mobility, and good dark-state resistance, making them have the potential to prepare photoconductive switches.

[0003] Currently, SiC photoconductive switches are often triggered by 532nm or 1064nm lasers, which are non-intrinsic absorption with a long absorption depth (greater than 0.7cm), which is much larger than the thickness of the substrate itself, resulting in insufficient absorption of incident light energy and limiting the improvement of conduction current. In addition, both traditional vertical photoconductive switches and planar photoconductive switches have the problems of large electrode atmosphere blocking light and mismatching of electric field and optical field, which also limits the improvement of the conduction performance of the device. SUMMARY

[0004] The present application aims to solve the above-mentioned problems in the prior art, and provides a photoconductive switch device with waveguide structure, which is suitable for non-intrinsic absorption photoconductive devices. By setting the waveguide coupling window, the front and back high-reflectivity electrodes, and the side anti-reflection film, the incident light is inclined at an angle greater than the critical angle of total reflection and then conducts laterally with low energy loss, significantly improving the effective absorption depth and utilization of incident light, while realizing the adaptation of electric field and optical field, which is beneficial to the rapid collection of photo-generated carriers, thereby effectively reducing the conduction resistance.

[0005] To achieve the above-mentioned purpose, the present application adopts the following technical solutions:

[0006] A photoconductive switch device with waveguide structure, comprising:

[0007] a dark-state high-resistance light-sensitive substrate, which simultaneously serves as a functional area of a photoconductor and a core layer of an optical waveguide;

[0008] a high-reflectivity front electrode and a high-reflectivity back electrode formed above and below the dark-state high-resistance light-sensitive substrate;

[0009] A side-side antireflective film formed on the sidewall of the dark-state high-resistivity photosensitive substrate;

[0010] A waveguide coupling window disposed on the dark-state high-resistivity photosensitive substrate is used to couple the light emitted by the trigger light source into the interior of the substrate at an angle greater than the critical angle of total internal reflection of the dark-state high-resistivity photosensitive substrate material, so that the light beam is transversely propagated within the substrate.

[0011] The upper and lower surfaces of the dark-state high-resistivity photosensitive substrate are further provided with highly doped regions; the highly doped regions are N⁺ type or P⁺ type, and the doping concentration is 1×10⁻⁶. 11 ~9×10 21 cm -3 The doping depth is no greater than 1 μm.

[0012] The material of the dark-state high-resistivity photosensitive substrate is an elemental semiconductor or a compound semiconductor, with a thickness of 10 to 2000 μm and a dark-state resistance of 1 MΩ to 100 GΩ; the elemental semiconductor includes Si, Ge or diamond; the compound semiconductor includes SiC, GaAs, GaN or Ga2O3.

[0013] The high-reflectivity front electrode and high-reflectivity back electrode are made of metal, metal alloy or non-metal conductive material, wherein the metal includes at least one of Au, Ag, Ti and Ni; the non-metal conductive material includes graphite, graphene, polycrystalline silicon or AZO; the high-reflectivity front electrode and high-reflectivity back electrode have a reflectivity of 30% to 99.5% at the device operating wavelength and an electrode thickness of 10 nm to 1 μm.

[0014] The side-mounted antireflective coating has a refractive index of 1–2.6, a thickness of 30–500 nm, and a reflectivity of 30%–99.5%.

[0015] The coupling methods of the waveguide coupling window include grating coupling, end face coupling, prism coupling, mode converter coupling, photonic crystal coupling, thermo-optical coupling, or electro-optical coupling, with a coupling efficiency of 30% to 99.5% and a beam coupling angle of 22° to 65°.

[0016] When the waveguide coupling window is a grating coupling, it is a tilted grating with an anti-reflection coating on top.

[0017] The triggering light source is a laser, LED, or xenon lamp, with an emission wavelength of 300nm to 10μm, an optical power of 1nW to 1GW, and a spot area of ​​1μm. 2 ~1cm 2 .

[0018] The deflection angle of the beam propagating laterally within the substrate is greater than the critical angle for total internal reflection but less than 180º.

[0019] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0020] 1. For scenarios involving intrinsic absorption, this invention is designed to fully absorb incident light energy, improve incident energy utilization, and ultimately reduce on-resistance and increase on-current.

[0021] 2. The present invention adopts an optical waveguide design to avoid the misalignment of the optical field and electric field caused by the electrode blocking light in the traditional structure, which is conducive to optimizing the conduction path of photogenerated carriers and improving the conduction performance.

[0022] 3. In this invention, the light-incident area and the electrode area are separated, which does not affect the design of the withstand voltage terminal, and at the same time avoids the problem of electric field concentration caused by the traditional structure setting of the light-incident window. Attached Figure Description

[0023] Figure 1 Here are schematic diagrams of the device structure in an embodiment of the present invention (a) and a comparative example device structure (b);

[0024] Figure 2 The diagram shows the diffraction angle and diffraction efficiency compass diagram (a) and the grating period and diffraction efficiency diagram (b) of the coupling grating according to an embodiment of the present invention.

[0025] Figure 3 The images show the light intensity distribution of the device (a) in this embodiment and the comparative device (b) when it is turned on at 10kV; wherein the laser wavelength used is 532nm and the optical power density is 2MW / cm². 2 ;

[0026] Figure 4 The diagram shows the current density distribution of the device (a) in this embodiment and the comparative device (b) when turned on at 10kV; wherein the laser wavelength used is 532nm and the optical power density is 2MW / cm². 2 ;

[0027] Figure 5 The figures show the on-current and voltage characteristic curves of the device in this embodiment and the comparative device; wherein the laser wavelength used is 532nm and the optical power density is 2MW / cm². 2 .

[0028] Figure label: High reflectivity front electrode 1, front P + 2. Highly doped region; 3. Dark-state high-resistivity photosensitive substrate; 4. Side anti-reflection film; 5. Backside P-coating. + 5. Highly doped region, 6. High reflectivity back electrode, 7. Trigger light source, 8. Vertically incident light, 9. Waveguide coupling window. Detailed Implementation

[0029] To make the technical problems, technical solutions and beneficial effects of the present invention clearer and more understandable, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0030] In this invention, the waveguide coupling window can be located on the front, back, or side of the device, and multiple waveguide coupling windows can exist simultaneously. The front electrode is located in the front non-transparent area and the grating coupling area, and the back electrode is located in the back non-transparent area and the grating coupling area. The incident direction of the trigger light source is front incident, back incident, or side incident. The above design is implemented according to actual needs, as long as the purpose of this invention is achieved. The following is an embodiment where the waveguide coupling window is located on the front of the device and the incident direction of the trigger light source is front incident.

[0031] Example 1

[0032] Figure 1 Figure (a) shows a schematic diagram of the cell structure of the photoconductive switch device with waveguide structure described in the embodiment, including:

[0033] High reflectivity front electrode 1, front P + 2. Highly doped region; 3. Dark-state high-resistivity photosensitive substrate; 4. Side anti-reflection film; 5. Backside P-coating. + 5. Highly doped region; 6. High reflectivity back electrode; 7. Trigger light source; 8. Waveguide coupling window;

[0034] The front P + The highly doped region 2 is formed on the upper surface of the dark-state high-resistivity photosensitive substrate 3, and the back surface P + A highly doped region 5 is formed on the lower surface of a dark-state high-resistivity photosensitive substrate 3, and the high-reflectivity front electrode 1 is formed on the front P. + The high-reflectivity back electrode 6 is formed on the upper surface of the highly doped region 2. + The lower surface of the highly doped region 5; the side reflective coating 4 is formed on the sidewall of the dark-state high-resistivity photosensitive substrate 3; the waveguide coupling window 9 is disposed on the dark-state high-resistivity photosensitive substrate 3.

[0035] The photoconductive switch device of this invention uses a dark-state high-resistivity photosensitive substrate 3 as both the light-conducting and conductive regions, a high-reflectivity front electrode 1 and a high-reflectivity back electrode 6 as both electrodes and upper and lower reflectors, and a side anti-reflection film 4 as both a passivation film to reduce leakage current and an anti-reflection film to reduce light leakage. This facilitates the coordinated control and effective utilization of the electric and optical fields and improves device performance. The waveguide coupling window 9 has a beam coupling angle greater than the corresponding total internal reflection critical angle of the substrate, and a light deflection angle greater than the total internal reflection critical angle but less than 180°, enabling lateral beam propagation within the substrate. The device structure described in this embodiment can be a vertical photoconductive switch, a horizontal photoconductive switch, or a pseudo-vertical photoconductive switch, i.e., it can adapt to both same-side and opposite-side electrode scenarios.

[0036] In this invention, the photoconductive switching device is controlled by the trigger light source 7 to turn on and off, and the substrate on-resistance value is adjusted by the magnitude of the light power.

[0037] The high-reflectivity front electrode 1 is a silver / gold stack with thicknesses of 50nm and 100nm, respectively. The silver layer has a reflectivity of 96% for incident light, and the gold layer acts as a protective layer to prevent the silver from oxidizing naturally, and is located on top of the silver layer.

[0038] The front P + The doping concentration of highly doped region 2 is 1×10⁻⁶. 19 cm -3 The thickness is 200nm.

[0039] The dark-state high-resistivity photosensitive substrate 3 is vanadium-doped SiC with a vanadium doping concentration of 1×10⁻⁶. 15 cm -3 It has a thickness of 500μm and a dark-state resistance of 1GΩ.

[0040] The side reflective coating 4 is an Al2O3 thin film, grown by atomic layer deposition, with a thickness of 79.5 nm, a refractive index of 1.67, and a reflectivity of 99.3% for 532 nm light.

[0041] The back side P + The doping concentration of highly doped region 5 is 1×10⁻⁶. 19 cm -3 The thickness is 200nm.

[0042] The high-reflectivity back electrode 6 is a silver / gold stack with thicknesses of 50nm and 100nm, respectively. The silver layer has a reflectivity of 96% for incident light, and the gold layer acts as a protective layer to prevent the silver from oxidizing naturally, and is located on top of the silver layer.

[0043] The trigger light source 7 is a 532nm laser with a spot area of ​​0.16cm². 2 The optical power density is 2MW / cm². 2The vertically incident light 8 emitted by the trigger light source 7 illuminates the waveguide coupling window 9.

[0044] The waveguide coupling window 9 is an inclined coupling grating with a tilt angle of 35°, a period of 250nm, a duty cycle of 50%, a grating depth of 300nm, and an anti-reflection film with a thickness of 30nm deposited on the top of the grating. The coupling efficiency is 97.5% and the coupling angle is 54.1°.

[0045] The following provides a specific embodiment of the fabrication technology, taking vanadium-doped SiC as an example only. The dark-state high-resistivity photosensitive substrate 3 can also be made of other semiconductor materials such as GaN, GaAs, Ga2O3, and diamond, and the process parameters need to be adjusted accordingly:

[0046] 1) Commercial vanadium-doped SiC wafers were cleaned using standard RCA, soaked in diluted hydrofluoric acid solution for 1 min, and then sonicated with ethanol and acetone for 5 min each.

[0047] 2) Atomic layer deposition: 50 nm Al2O3 is grown on the front and back sides and sidewalls of the sample. The Al2O3 on the sidewalls is used as an anti-reflection film, and the front and back sides are used as insulating layers for ion implantation to increase the surface doping concentration.

[0048] 3) Ion implantation on both sides, using a box-shaped distribution, with a total ion implantation concentration of 1×10⁻⁶. 19 cm -3 .

[0049] 4) Sputter 100nm carbon films on both sides, then perform ion implantation activation by annealing at 1620℃ for 30min in an argon atmosphere.

[0050] 5) Remove carbon film by high-temperature oxidation at 760℃ for 1 hour.

[0051] 6) Photolithography and ICP etching to remove all Al2O3 films from the back and front active areas.

[0052] 7) Photolithography, ICP etching, etching a 20nm Al2O3 thin film in the light-incident region.

[0053] 8) Electron beam exposure develops the top region of the grating.

[0054] 9) Evaporate 50nm chromium as a metal mask.

[0055] 10) ICP is used to etch 30nm Al2O3 and 300nm SiC at a 35° angle to form a tilted grating with a top antireflection film.

[0056] 11) Soak in chromium etching solution for 2 hours to completely remove the metal mask.

[0057] 12) Photolithography, sputtering of the front electrode, and stripping.

[0058] 13) Sputtering the back electrode.

[0059] Comparative Example

[0060] See comparison examples Figure 1 As shown in Figure (b), it is a schematic diagram of the cell of the comparative device. Its basic parameters and process flow are similar to those of this embodiment, but no additional tilted grating is fabricated.

[0061] Figure 2 The figures (a) and (b) are the diffraction angle and diffraction efficiency compass diagrams of the coupled grating in this embodiment of the invention. As can be seen from the figures, after the tilted grating parameters are designed, the incident light source is perpendicularly incident on the tilted coupled grating, the beam is deflected by 54.01°, and the energy is concentrated in the +1 diffraction energy level, with a diffraction efficiency of 97.5%. This figure of merit is obtained at a grating period of 250 nm.

[0062] Figure 3 The images show the light intensity distribution of device (a) and comparative device (b) in this invention when turned on at 10kV, wherein the laser wavelength used is 532nm and the incident light power density is 2MW / cm². 2 As shown in the figure, in the device of this embodiment, the light intensity is deflected and totally reflected after being coupled into the grating, and returns after contacting the anti-reflective film on the side wall, which improves the light utilization rate. In contrast, most of the light in the comparative device is reflected by the electrodes, and the light intensity is only distributed in the light-transmitting window and is not fully absorbed.

[0063] Figure 4 The current density distribution of the device (a) in this embodiment and the comparative device (b) when turned on at 10kV is shown. The laser wavelength used is 532nm and the optical power density is 2MW / cm². 2 As can be seen from the figure, the current density distribution in the device of the embodiment is more uniform than that in the comparative device. This is attributed to the fact that the photoconductive switch device with waveguide structure achieves perfect matching between electric field and optical field and provides a more uniform conduction path for photogenerated carriers.

[0064] Figure 5 The on-current and voltage characteristic curves of the device in this embodiment and the comparative device are shown. The laser wavelength used is 532nm and the optical power density is 2MW / cm². 2 Under the same test conditions, the waveguide-structured photoconductive switch device of the present invention exhibits significantly improved performance compared to traditional devices, with the conduction current density increasing from 2497 A / cm². 2 Increased to 17595A / cm 2 The overall improvement is approximately 605%.

[0065] In summary, this invention significantly extends the effective optical path of photoconductive switching devices for non-intrinsic wavelengths, ensuring full absorption of incident light, effectively improving the device's photoresponsivity and photocurrent, and reducing on-resistance. On the other hand, it solves the photoelectric field mismatch problem caused by the metal electrodes blocking light in traditional photoconductive devices. At the same time, the light-incident area is isolated from the electrode area, avoiding the problem of electric field concentration caused by the microstructure of the optical surface, which is beneficial to improving the device's blocking capability.

[0066] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A photoconductive switching device with a waveguide structure, characterized in that, include: A dark-state high-resistivity photosensitive substrate that simultaneously serves as the functional region of a photoconductor and the core layer of an optical waveguide; High-reflectivity front electrode and high-reflectivity back electrode are formed on and below the dark-state high-resistivity photosensitive substrate; A side-side antireflective film formed on the sidewall of the dark-state high-resistivity photosensitive substrate; An inclined grating waveguide coupling window disposed on the dark-state high-resistivity photosensitive substrate is used to couple light emitted from the trigger light source into the interior of the substrate at a single angle greater than the critical angle of total internal reflection of the dark-state high-resistivity photosensitive substrate material, so that the light beam is laterally propagated within the substrate by total internal reflection; wherein, the light incident region is isolated from the electrode region.

2. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The upper and lower surfaces of the dark-state high-resistivity photosensitive substrate are further provided with highly doped regions; the highly doped regions are N... + Type or P + Type, doping concentration of 1×10 11 ~9×10 21 cm -3 The doping depth is no greater than 1 μm.

3. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The material of the dark-state high-resistivity photosensitive substrate is an elemental semiconductor or a compound semiconductor, with a thickness of 10 to 2000 μm and a dark-state resistance of 1 MΩ to 100 GΩ; the elemental semiconductor includes Si, Ge or diamond; the compound semiconductor includes SiC, GaAs, GaN or Ga2O3.

4. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The high-reflectivity front electrode and the high-reflectivity back electrode are made of metallic or non-metallic conductive materials. The metallic materials include at least one of Au, Ag, Ti, and Ni. The non-metallic conductive materials include graphite, graphene, polycrystalline silicon, or AZO. The high-reflectivity front electrode and the high-reflectivity back electrode have a reflectivity of 30% to 99.5% at the device's operating wavelength, and the electrode thickness is 10 nm to 1 μm.

5. A photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The side-mounted antireflective coating has a refractive index of 1–2.6, a thickness of 30–500 nm, and a reflectivity of 30%–99.5%.

6. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The top of the tilted grating is coated with an anti-reflection film, with a coupling efficiency of 30% to 99.5% and a beam coupling angle of 22° to 65°.

7. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The triggering light source is a laser, LED, or xenon lamp, with an emission wavelength of 300nm to 10μm, an optical power of 1nW to 1GW, and a spot area of ​​1μm. 2 ~1cm 2 .

8. The photoconductive switching device with a waveguide structure as described in claim 1, characterized in that: The deflection angle of the beam propagating laterally within the substrate is greater than the critical angle for total internal reflection but less than 180°.

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