SiC Photoconductive Semiconductor Switches Research Articles

Influence of optical grating on the triggering efficiency of VCSI silicon carbide photoconductive semiconductor switch

In this article, we present a new configuration of opposed-contact vanadium-compensation semi-insulating (VCSI) 4H–SiC photoconductive semiconductor switch (PCSS) to reduce the input laser energy for operation. The configuration is made up of three parts: the PCSS with optical grating, the convex lens in front of PCSS, and the additional reflector behind PCSS. Periodic surface structures were fabricated on the VCSI 4H–SiC substrate by ultrafine femtosecond laser direct writing to etch optical gratings. The microstructure on the lower surface plays the role of reflection grating, so that the laser forms a specific distribution pattern and enhances the laser absorption. Experiments and simulations show that the triggering efficiency increased 3.7 times compared to PCSS without grating at 532 nm laser. And output voltage can reach 90 % of the input bias voltage. This SiC PCSS optical system significantly reduces the laser energy without reducing the electrodes spacing.

Investigation on the photocurrent tailof vanadium-compensated 4H–SiC for microwave application

Vanadium-compensated semi-insulating 4H–SiC photoconductive semiconductor switch (PCSS) has been a promising candidate for frequency-agile microwave generation. This application usually requires the PCSS to operate in linear mode so that a short carrier lifetime is required. However, in our experiment, some samples showed a long tail of photocurrent when illuminated with 532 nm light. To investigate the cause of the tail, we performed photocurrent tests at 532 and 1064 nm for two 4H–SiC samples with different doping. From the experimental results, we deduce that the cause is a hole trap that was not investigated previously. To verify it, we constructed a versatile transient simulation model of 4H–SiC triggered at sub-bandgap light. The model can deal with amphoteric V in steady state, the extrinsic light absorption and recombination process with more than one trap level. The simulation results agree well with the experiments. By characterizing the properties of the trap, we deduce that the unintentional doping of aluminum’s shallow acceptor level functions as the hole trap.

Dependence of conduction characteristics on compensation type and lattice structure of SiC photoconductive semiconductor switches.

Semi-insulating (SI) SiC photoconductive semiconductor switches were prepared using two compensation mechanisms: namely vanadium dopants compensation (4H- and 6H-SiC) and deep level defect compensation (4H-SiC). The bias voltage and current of the high-purity (HP) SI 4H-SiC photoconductive semiconductor switch (PCSS) with a channel length of 1 mm reached 24 kV and 364 A, respectively, and the minimum on-state resistance of approximately 1 Ω was triggered by laser illumination at a wavelength of 355 nm. The experimental results show that, in this case, the on-state characteristics of HP 4H-SiC PCSS are superior to those of the vanadium-doped(VD) 4H and 6H-SiC PCSS devices. HP 4H-SiC PCSS shows remarkable waveform consistency. Unlike for VD 4H and 6H-SiC PCSS, the current waveform of HP 4H-SiC PCSS exhibits a tailing phenomenon due to its longer carrier lifetime.

Initial Test of Optoelectronic High Power Microwave Generation From 6H-SiC Photoconductive Switch

High-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. This letter presents a design and initial test of an optoelectronic class B push-pull microwave power amplifier (MPA) using two 6H-SiC photoconductive switches. The initial tests have been conducted with bias voltage of ±2.4 kV, at 80 kW peak laser pulse power, demonstrating that the SiC PCSS working in linear mode can produce microwaves. Then, circuit simulation is conducted to study the factors affecting the electrical efficiency, such as the quantum efficiency, the peak laser pulse power, and the bias voltage. It is speculated that the MPA could output 1 mW microwave power and achieve electrical efficiency of more than 60% with a bias voltage of 15 kV, quantum efficiency of 0.2, and peak laser pulse power of 100 kW.

550-W Ultraviolet Exciplex Source for Pulsed Power Applications

The investigation of a high output power, arc lamp exciplex ultraviolet (UV) source for pulsed power applications is presented. The arc lamp generates up to 550 W from XeF * exciplex radiation at 351 nm, totaling to nearly 0.15-mJ total radiated UV energy over the duration of the UV pulse. With an ellipsoidal reflector, the arc lamp produces 400 W/cm 2 and up to 0.1 mJ of UV light onto a 1-cm 2 area. A complete experimental investigation of the arc lamp for both XeCl * (308 nm) and XeF * (351 nm) exciplex sources operated under varying excitation and pressure conditions is reported. As an application, the arc lamp is successfully utilized as an illumination source for an intrinsically triggered, wide bandgap SiC photoconductive semiconductor switch (PCSS), where a PCSS ON-state resistance of 500 Ω is achieved.

Application of an Al-doped zinc oxide subcontact layer on vanadium-compensated 6H–SiC photoconductive switches**Project supported by the Innovation Program of the Shanghai Institute of Ceramics (Grant No. Y39ZC1110G), the Innovation Program of the Chinese Academy of Sciences (Grant No. KJCX2-EW-W10), the Industry–Academic Joint Technological Innovations Fund Project of Jiangsu Province, China (Grant No. BY2011119), the Natural Science Foundation of Shanghai (Grant

Al-doped ZnO thin film (AZO) is used as a subcontact layer in 6H–SiC photoconductive semiconductor switches (PCSSs) to reduce the on-state resistance and optimize the device structure. Our photoconductive test shows that the on-state resistance of lateral PCSS with an n+-AZO subcontact layer is 14.7% lower than that of PCSS without an n+-AZO subcontact layer. This occurs because a heavy-doped AZO thin film can improve Ohmic contact properties, reduce contact resistance, and alleviate Joule heating. Combined with the high transparance characteristic at 532 nm of AZO film, vertical structural PCSS devices are designed and their structural superiority is discussed. This paper provides a feasible route for fabricating high performance SiC PCSS by using conductive and transparent ZnO-based materials.

Preparation and Properties of Lateral Contact Structure SiC Photoconductive Semiconductor Switches

A series of lateral structural photoconductive semiconductor switches(PCSS) were fabricated on V-doped semi-insulating 6H-SiC substrate with the Ni/Au contacts.These PCSS were measured with different bias voltages, excitation energies and excitation wavelengths.The photoelectric absorption effect and photoelectric response of SiC PCSS were investigated.It is found that the absorption coefficient is between 0.601 and 0.692 mm–1 for semi-insulating 6H-SiC substrate when it is excited by 532 nm laser,and the corresponding pulse signal is much smaller than that excited by 1064 nm laser.Nanosecond-pulse signal is obtained for 6H-SiC PCSS excited by 532 nm laser.The peak current flowing through the switch is increased with increasing the bias voltage and excitation energy, while it is decreased with the increase in substrate thickness.

Effect of Surface Morphology on the On-State Resistance of SiC Photoconductive Semiconductor Switches

The photoconductive semiconductor switches (PCSS) were fabricated on V-doped semi-insulating 6H-SiC. We studied the effect of surface morphology on the on-state resistance of SiC PCSS. The SiC wafers with quite similar physical properties were processed by mechanical polishing, chemical mechanical polishing and H2 etching for producing different surface morphologies. All the SiC PCSS were excited by a 355 nm laser with a frequency of 10 Hz and a pulse intensity of 132 μJ/mm2. We found that the surface morphology had an obvious effect on the on-state resistance. The PCSS fabricated on mechanical polished SiC wafer with an average surface roughness (rms) of 1.0 nm showed the largest on-state resistance of 45.6 ohms, while a low value of 13.3 ohms was observed for the wafer processed by H2 etching at high temperature of 1550 °C.

影响碳化硅光导开关最小导通电阻的因素

影响碳化硅光导开关最小导通电阻的因素

大功率光导开关研究

In this paper semi-insulating GaAs photoconductive semiconductor switch(PCSS) and SiC PCSS were fabricated. Triggered by laser pulse at a wavelength of 1 064 nm, photoconductivity tests of the PCSSs were performed at different bias voltages. Dark current-voltage characteristics of GaAs PCSS and the absorption depth of GaAs with different wavelength were obtained experimentally. GaAs PCSSs both in linear mode and nonlinear mode were studied, and peculiar photoconductivity of high-power GaAs PCSS in nonlinear mode was discussed. High-power SiC PCSSs employing extrinsic photoconductivity are under development, and initial experimental results are presented in this paper.

Super Fast and High Power SiC Photoconductive Semiconductor Switches

High-power photoconductive semiconductor switches (PCSS) were fabricated on 0.2at% vanadium-doped semi-insulating 6H-SiC (7.0×10~8Ω·cm).V-doped 6H-SiC PCSS with 1mm gap displays a fast rise time (6.8ns),short photoconductivity pulse width (less than 20ns) and high-speed photovoltaic response to 20ns laser pulse.The experimental results show that the linear peak voltage is increased with increasing bias voltage and excitation energy.The typical maximum photocurrent of the device at 2.5kV is about 57.5A,the peak electrical power delivered to a 40Ωload is 132kW.