Silicon Carbide Photoconductive Switch Research Articles

Breakdown behavior of SiC photoconductive switch with transparent electrode

The breakdown behavior of a V-doped 4H silicon carbide photoconductive switch with a transparent electrode under a high electric field is studied. The device is triggered by a laser pulse below the bandgap wavelength with a repetition rate of 100 Hz. The light peak-power of the laser pulse reaches hundreds of kW, and the bias voltage is increased from 10 to 20 kV. With the accumulation of the number of pulses, the device shows breakdown behavior. Through the microscopic diagnosis of damaged and breakdown devices, according to the analysis of theoretical and simulation results, the breakdown of the device is due to the interaction between the laser and the aluminum doped zinc oxide transparent electrode on the device surface, resulting in the melting of the transparent electrode. The direct illuminate of the laser can form a field enhancement effect at the junction of the substrate and the transparent electrode, resulting in the damage of the device and the formation of pre-breakdown. Finally, the breakdown of the device inevitably occurs.

Effects of High-Field Velocity Saturation on the Performance of V-Doped 6H Silicon-Carbide Photoconductive Switches

Velocity saturation characteristics of a V-doped 6H silicon-carbide (SiC) photoconductive switch under high electric field are presented. A vertical-geometry switch device based on vanadium-compensated SiC is triggered by a 532-nm laser pulse with light peak power of several hundred kW and operational voltages from 2 to 20 kV. The maximum electrical peak power achieved by the device is up to 1 MW (~50-A, 20-kV, 1.1-ns pulsewidth). When the working voltage is increased to increase output power, the carrier-velocity saturation under high electric field unavoidably impedes the current growth and directly limits the peak power. The parameters of parallel high-field-dependent mobility are obtained with different fields and laser energies: low-field mobility μ = 227 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V s and fitting parameter β = 1.7. With working voltage increasing steadily, a crack-forming process results in device degradation as a result of large current and high electric field. The I - V characteristic curves of the simulations and tests show current saturation and possible damage under high electric field.

Performance Modeling of Silicon Carbide Photoconductive Switches for High-Power and High-Frequency Applications

In this article, we focus on the physical modeling of the nonlinear operation of intrinsic photoconductive semiconductor switches (PCSS) based on 4H-SiC using coupled electrical and optical simulations to provide performance bounds of the switch as a function of material and geometry parameters, as well as applied bias. We also conduct a full design-space exploration to identify the optimal operating and design conditions to maximize the compound metric $f_{\mathrm {op}} P_{\mathrm {out}}$ , where $f_{\mathrm {op}}$ is the maximum operating frequency, and $P_{\mathrm {out}}$ is the maximum output power the switch can provide. We quantify that a 10- $\mu \text{m}$ long and 5- $\mu \text{m}$ thick 4H-SiC PCSS can deliver output power density greater than 2W/mm at 150 GHz when triggered by a 0.325- $\mu \text{m}$ laser with intensity of 3 kW/cm2. The output power density can be significantly enhanced by increasing the optical generation rate as well as by using thicker SiC to improve its absorption characteristics. A brief discussion of signal distortion and electrostatic screening effects at high optical bias is included. Finally, we present an analytic model of charge cloud propagation and the frequency of operation based on the physics, material parameters, and geometry of the PCSS. The model accurately captures $f_{\mathrm {op}}$ of 4H-SiC PCSS over a broad range of laser spot size, device length, and electrical bias applied at the contacts.

4H-SiC photoconductive switch with low on-state resistance

4H-SiC photoconductive switches with a lateral geometry are fabricated. Phosphate ion implantation is adopted to decrease the resistance. The results show that phosphate ion implantation can effectively reduce the resistance nearing the electrode and the minimum unit of the electrode gap on-state resistance is 3.17 / mm. This experiment shows the bias voltage and optical pulse energy how to effect the on-state resistance. The power of the device is more than 2.0 MW when the bias voltage is 10 kV and the energy of light is 30.5 mJ. The characteristics of the switch output are stable, low jitter and high power. This is of importance to the application of silicon carbide photoconductive switch.

Effects of substrate crystallinity on the on-state resistance of 6H–SiC photoconductive switches

Abstract

Design and characterization of silicon carbide photoconductive switches for high field applications

Characteristics of a silicon carbide photoconductive switch designed for high field applications have been studied. Analyses show that premature breakdown occurs primarily due to impact ionization and subsequent charge accumulation near the anode. For the shallow donor, deep-acceptor-type compensated material, a p+ layer next to the cathode results in field homogenization in the bulk. As a result, the blocking or hold off voltage of the switch could increase beyond the experimentally determined value of 18kV (0.45MV∕cm). Simulations also show that a minimum thickness, equivalent to a diffusion length, of the p+ layer is necessary to avoid premature breakdown. Following illumination, the photocurrent rise time of the switch would also improve by about 25% with the p+ layer near the cathode.

Silicon carbide photoconductive switch for high-power, linear-mode operations through sub-band-gap triggering

The analysis of a 6H silicon carbide (SiC) photoconductive switch, designed and packaged for high-power, linear-mode operations, is presented. The switch, fabricated from semi-insulating compensated SiC, is triggered by an optical source with photon energy less than the band-gap energy. Simulation models incorporating the effects of vanadium trap and nitrogen dopant in the compensation material show I-V characteristics that agree with measured values. The photoconductive switch has improved rise-time characteristics as compared to a gallium arsenide (GaAs) switch. The analysis also shows that improved performance at high power is possible through passivation using high-permittivity dielectric near the contact-semiconductor interface and by placing a p+ layer next to the cathode.