High-power Photoconductive Semiconductor Switches Research Articles

Influence of Hot-Carriers on the On-State Resistance in Si and GaAs Photoconductive Semiconductor Switches Working at Long Pulse Width**Supported by the Rector’s Fund of China Academy of Engineering Physics (Grant No. YZJJLX2016002), and the National Natural Science Foundation of China (Grant Nos. 61504127 and U1530128).

We demonstrate that the transport of hot carriers may result in the phenomenon where an oscillated output current appears at the waveforms in a high-power photoconductive semiconductor switch (PCSS) working at long pulse width when the laser disappears or the electric field changes. The variational laser and electric field will affect the scattering rates of hot carriers and crystal lattice in high-power PCSS, and the drift velocity of hot carriers and also the on-state resistance will be changed. The present result is important for reducing the on-state resistance and improving the output characteristics of high-power Si/GaAs PCSS.

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.

The Test of a High-Power, Semi-Insulating, Linear-Mode, Vertical 6H-SiC PCSS

A high-power photoconductive semiconductor switch (PCSS) working in linear mode can be used for RF generation by modulating the illuminating light. Such a PCSS constructed of a semi-insulating 6H silicon carbide (6H-SiC) substrate and its characterization under a high electric field is presented. The PCSS is of a vertical structure, with one hollow/transparent electrode to let through the laser light and the other highly reflective to increase light absorption. First, to optimize the high-voltage withstanding, the factors affecting the field enhancement, such as substrate thickness, electrode profiles, and encapsulating materials, are discussed. Then, the PCSS is assembled and tested, and the 0.8-mm-thick 6H-SiC PCSS is able to work with electric fields up to 225 kV/cm and the power capacity up to 10.6 MW without failure when triggered by a Nd:YAG laser (532-nm, 17-ns full wavelength at half maximum). By varying the optical energy from 3 to 31.9 mJ, the minimum conducting resistance and the peak photocurrent of the PCSS are obtained. The PCSS fails with further increasing voltage, and the cause of the failure was identified to be a bulk breakdown. The result shows that the PCSS can work linearly and it is possible to be used in high-power compact RF generation.

Fabrication and properties of V-doped semi-insulating 6H-SiC photoconductive semiconductor switch

High power photoconductive semiconductor switches (PCSSs) were fabricated on V-doped semi-insulating 6H-SiC single crystal. The 6H-SiC PCSS were measured by applying a bias voltage from 1 kV to 14 kV. The triggered laser was a 355 nm pulse laser with an energy density of 150 J/mm2. The peak photocurrent shows an increasing trend with improving the applied voltage. The peak photocurrent running through the PCSS and the calculated on-state resistance are 185 A and about 22 respectively when the applied voltage reaches 14 kV, and the corresponding peak power is 2.59 MW.

V掺杂6H-SiC光导开关制备与性能研究

High power photoconductive semiconductor switches (PCSSs) were fabricated on V-doped semi-insulating 6H-SiC single crystal. The 6H-SiC PCSS were measured by applying a bias voltage from 1 kV to 14 kV. The triggered laser was a 355 nm pulse laser with an energy density of 150 J/mm2. The peak photocurrent shows an increasing trend with improving the applied voltage. The peak photocurrent running through the PCSS and the calculated on-state resistance are 185 A and about 22 respectively when the applied voltage reaches 14 kV, and the corresponding peak power is 2.59 MW.

大功率光导开关硅微通道散热器设计与测试

大功率光导开关硅微通道散热器设计与测试

11 kV大功率SiC光电导开关导通特性

A high-power photoconductive semiconductor switch(PCSS) has been fabricated by semi-insulating silicon carbide crystal. The width of the output voltage pulse was about 40 ns and the rise-time was 9.6 ns, when a KrF excimer laser was adopted as the excitation source. Two different steps were observed in the rising edge. With the input voltage rising from 1 kV to 11 kV, the on-state resistance remained about 12 Ω. The peak current through the PCSS came to be 159 A with the 11 kV input voltage, while the peak power reached 1.4 MW. No carrier saturation has been observed in the experiment.

影响高功率光导开关临界频率热因素的数值分析

影响高功率光导开关临界频率热因素的数值分析

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.

Two post-breakdown metastable phases in semi-insulating GaAs

A room temperature electrically induced metastability in semi-insulating (SI)-GaAs has recently been reported in which the normally high resistivity state of SI-GaAs converts into a low resistance state when breakdown electric fields are applied to the metal/SI-GaAs/metal system. The present study finds that this post-breakdown metastable state can be classified into two metastable phases, namely a metastable high current phase and a metastable low current phase. This effect resembles the poorly understood ‘lock-on’ effect utilized in high power photoconductive semiconductor switches. It is argued that instead of a short pulse of light photo-ionizing the SI-GaAs and causing a carrier avalanche current that does not ‘switch off’ at low biases, the same avalanche current and effects are being brought about by the electrical breakdown of the sample.

Modeling of high power semiconductor switches operated in the nonlinear mode

Although optically activated high power photoconductive semiconductor switches (PCSS) are usually triggered using uniform illumination, under select conditions they can be activated and closed in <1 ns with a spot of light near the contacts. This observation requires free carriers to either travel at speeds faster than their saturation velocity or for there to be a carrier generation mechanism that propagates with similar speeds. A two-dimensional time-dependent computer model of a GaAs high power switch has been employed to investigate these observations, and activation of PCSS by spots of light in particular. Results from the model suggest that the transport of band-to-band recombination radiation plays an important role in propagating electrons across the switch when the switch is closed with a spatially nonuniform laser pulse. Reabsorption of the recombination radiation and photogeneration of carriers is a mechanism which generates free carriers in the gap between the contacts at speeds greater than saturation velocity. The results also indicate that the switch is sensitive to the location of the activating laser pulse. Less laser fluence is required to close the switch if illumination occurs near the cathode rather than near the anode.

Triggering GaAs lock-on switches with laser diode arrays

Progress toward the triggering of high-power photoconductive semiconductor switches (PCSSs) with laser diode arrays, is reported. An 850-W optical pulse from a laser diode array was used to trigger a 1.5-cm-long switch that delivered 8.5 MW to a 38.3- Omega load. Using 166-W arrays, it was possible to trigger a 2.5-mm-long switch delivering 1.2 MW with 600-ps rise-times at pulse repetition frequencies of 1 kHz. These 2.5-mm-long switches survived 10/sup 5/ pulses at 1.0 MW levels. In single-pulse operation, up to 600 A was switched with laser diode arrays. The goal is to switch up to 5 kA in a single-shot mode and up to 100 MW repetitively at up to 10 kHz. At electric fields below 3 kV/cm GaAs switches are activated by creation of one electron-hole pair per photon. This linear mode demands high laser power and, after the light pulse, the carriers recombine in nanoseconds. At higher electric fields GaAs acts as a light-activated Zener diode. The laser light generates carriers as before, but the field induces gain such that the amount of light required to trigger the switch is reduced by a factor of up to 500. The gain continues until the field across the sample drops to a material-dependent lock-on field. The gain in the switch allows for the use of laser diodes.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Optical control of semiconductor closing and opening switches

Recent progress in the research of high-power photoconductive semiconductor switches is reviewed. Material issues and switch design considerations are discussed. High-power ultra-wide-band microwave generation using these switches and a pulse-forming network is presented. The application of the photoconductive switch both as a closing and and as an opening switch in an inductive energy storage system has been demonstrated. Electric pulse compression with a peak power gain of 30 has been observed. Future prospects in this area of research are discussed. >