Semi-insulating GaAs Photoconductive Semiconductor Switch Research Articles

利用高速GaAs光电导开关实现腔倒空激光脉冲输出

Cavity dumping is an effective technique for generating q-switched laser pulses of relatively large energy and extremely short time duration, and the width of q-switched pulses is primarily a function of the oscillator cavity length. the solid state lateral semi-insulating gaas photoconductive semiconductor switch (pcss) has the unique ability to handle high power at very fast response time with very little timing jitter. a novel and effective technique of cavity dumping laser for generating short q-switched laser pulses with a gaas pcss is presented. in a flashlamp pumped nd:yag laser with 20 cm long stable resonator, 1.7 ns short laser pulses have been obtained, and the pulse to pulse duration instability is less than 7% and energy instability is less than 3%.

Research on electrical pulse of 20-kV/30-Hz GaAs photoconductive switches

Photoconductive semiconductor switches (PCSSs) are widely used in high power ultra-wideband source applications and precise synchronization control due to their high power low-jitter high-repetition-frequency. In this letter, a 14-mm gap semi-insulating GaAs PCSS biased under 20 kV is triggered by a 1064-nm laser with a repetition frequency of 30 Hz. Although the trigger condition is greater than the threshold of the lock-on effect, the high gain mode is not observed. The results indicate that the high gain mode of the PCSS is quenched by decreasing the remnant voltage of pulsed energy storage capacitor.

Peculiar Photoconductivity in High-Power Semi-Insulating GaAs Photoconductive Semiconductor Switch

A photoconductive semiconductor switch (PCSS) with a gap of 0.018 m was fabricated from semi-insulating (SI) GaAs and tested under different bias voltages by using a laser at a wavelength of 1064 nm for triggering. The peculiar photoconductivity in high-power SI GaAs PCSS is reported. The PCSS operates in linear mode at bias voltages of 4 and 6 kV, because the waveform of photocurrent is similar to that of laser pulse. As the bias voltage increases, the full-width at half-maximum of photocurrents also increases, and the PCSS undergoes transition from linear to nonlinear mode. The switch behaved nonlinearly at a bias voltage of 10 kV, with obvious lock-on in photocurrent waveform. However, with bias voltages above 10 kV, the photocurrents increase instead of staying on a constant value, and a two-stage rise of photocurrents is observed. In both linear and nonlinear modes, photocurrents have the same full pulse duration at different bias voltages.

Operation of Pulse-Charged Spark Gap Triggered by GaAs Photoconductive Semiconductor Switch

The operation of a pulse-charged spark gap that is triggered by gallium arsenide (GaAs) photoconductive semiconductor switches (PCSSs) was investigated. By measuring the currents with the streamer discharge, we analyzed the mechanisms of breakdown between the semi-insulating GaAs PCSS and the spark gap. Two similar combination setups were studied by different gap structures. It was shown that the PCSS was a good candidate for generating high current (as high as 5.6 kA) or ultrafast pulse with 220-ps rise time and 400-ps full-width at half-maximum accompanied with good reproducibilities of waveforms.

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.

A high-voltage and high-current photoconductive semiconductor switch and its breakdown characteristics

Semi-insulating GaAs photoconductive semiconductor switch (PCSS) with withstand voltage of 32 kV and peak current of 3.7 kA has been developed. The breakdown mechanism of the PCSS is analyzed. It is shown that the breakdown of PCSS fabricated from indirect band-gap semiconductors is determined mainly by limited conduction of trap filling, but for PCSS's fabricated from materials that exhibit the transferred-electron effect, such as GaAs, breakdown of the PCSS is caused mainly by the negative-resistance-induced electric field enhancement at the anode boundary. Based on the Gunn effect electronics, the breakdown voltage of the semi-insulating GaAs PCSS is calculated, and the calculated results agree with the experimental results.

Characteristics of photoconductivity oscillation in semi-insulating GaAs photoconductive semiconductor switches

The 4 mm gap and 5 ns pulse width semi-insulating GaAs photoconductive switches were triggered by 532 nm laser pulse with gradual increase of bias voltage from 500 V in steps of 50 V until the emergence of nonlinear electrical pulse. The expermental results showed that the linear and nonlinear electrical pulse waveforms had smaller amplitude and varying degrees of oscillation reduction after going through a main pulse. Then the microscopic state and transport process of carriers （hot-electron） in the switch material were studied in detail using the quantum theory. It was found that in the DC bias electric field, when the relaxation time of the hot-electrons in the electron-electron and electron-phonon interaction process is longer than the carrier life, the photoconductivity oscillation can be caused by the change of mobility in the process of optoelectronic transport, which is the main cause for the output electrical pulse to show oscillations.

Analysis of operation mechanism of semi-insulating GaAs photoconductive semiconductor switches

This paper reports that the quenched-domain mode of luminous charge domain has been observed in semi-insulating (SI) GaAs photoconductive semiconductor switches (PCSSs) and the typical characteristics of lock-on effect have been explained based on the model of luminous charge domain. It is shown that the domain is formed by photogenerated carriers and the quenched domain is due to the interaction of the circuit self-excitation and transferred-electron oscillation in the bulk of switch. During the transit of the domain, the bias electric field (larger than Gunn threshold) across the switch is modulated by the ac electric field, when the instantaneous bias electric field is swinging below the sustaining field (the minimum electric field required to support the domain), and then the quenched-domain mode is obtained. When PCSSs operate in nonlinear mode, the ultrahigh electric field of domain induced by photogenerated carriers leads to strong impact ionization accompanied by electron-hole recombination radiation in the switch. Therefore new avalanche domains can be nucleated uninterruptedly by the carriers generated by absorption of recombination radiation which causes the effective carrier velocities to be larger than the saturation velocity. Lock-on field resulted from the length proportional number of domains and steadfast electric fields inside and outside the domains, and the recovery of lock-on effect is caused by the domain quenching. The calculations agree with the experimental results, and the analysis also indicates that SI-GaAs PCSS is a photoactivated charge domain device.

Multiple charge domains model for the lock-on effect in GaAs power photoconductive switches

This paper reports that the lock-on field of semi-insulating (SI) GaAs photoconductive semiconductor switches (PCSSs) was measured under different bias voltages. Based on the experimental results and the transferred-electron effect, a model for the lock-on effect in GaAs PCSSs is proposed. It is shown that the charge domain with an ultrahigh electric field is due to a high photogenerated carrier density, which gives rise to intensive impact ionization accompanied by electron–hole recombination radiation within the domain. Since new domains can be nucleated uninterruptedly by the carriers generated by absorption of recombination radiation, the forefront domain crosses the switch at a speed alternating between the photon velocity and the carrier saturated drift velocity, which makes the observed velocity of carriers larger than the saturated drift velocity. The lock-on field results from the fixed number of a moving train of avalanching charge domains, the steady-state domains electric fields and the steadfast external electric field of the domains. The recovery of the lock-on effect is caused by domain quenching. The calculations agree with the experimental results. Moreover, the analytical results indicate that SI-GaAs PCSS is essentially a type of photo-activated charge domain device.

30 kV and 3kA semi-insulating GaAs photoconductive semiconductor switch

Current as high as 3.7kA has been generated using a single photoconductive semiconductor switch (PCSS) excited by a laser pulse with the energy of ∼8mJ and under a bias of 28kV. The PCSS with electrode gap of 14mm was fabricated from semi-insulating GaAs. Under different bias voltages the “on” resistances of the PCSS were measured. The longevity of the PCSS reached 350 shots at 20kV and 400A. The breakdown mechanism of the PCSS is analyzed based on the breakdown characteristics. It is shown that the breakdown of GaAs PCSS can be described by the electron-trapping breakdown theory.

Mechanism analysis of periodicity and weakening surge of GaAs photoconductive semiconductor switches

The authors analyze the periodicity and weakening surge of semi-insulating GaAs photoconductive semiconductor switches. It is shown that the periodicity and weakening surge of the output current wave form is caused by the self-excitation of the circuit. The electric field threshold ET and the sustaining electric field Es (the minimum electric field required to support the domain) are modulated by the ac electric field; the output wave form becomes two main modes of transelectron oscillator, namely, delayed domain mode and quenched domain mode.

Generation of steady and jitter-free ultra-fast electrical pulses with GaAs photoconductive switches

In this paper, experiments of a lateral semi-insulating GaAs photoconductive semiconductor switch triggered by nanosecond, pico-second and femto-second laser pulses were reported. The switches was insulated by solid multi-layer transparent dielectrics. Jitter-free electrical pulse with steady voltage amplitude from the 1mm-gap GaAs switches was observed when biased with a low voltage and triggered by the serial laser pulses. Its change of amplitude was less than 1.2%, the triggered jitter-time was less than 10ps, and pulse width was up to sub-nanosecond. The effect of pulse energy change on the amplitude generated photoconductive semiconductor switch was analyzed. It was indicated that ultra-fast electrical pulse with steady voltage amplitude and pico-second triggered jitter-time can be obtained by controlling switch trigger condition and optimizing the switch design.

Compensation mechanisms and the response of high resistivity GaAs photoconductive switches during high-power applications

Photoconductive semiconductor switches (PCSSs) made from semi-insulating (SI) GaAs are the primary switching component of one class of high-power, ultra-wideband (UWB) microwave sources. The high resistivity of the GaAs can be achieved through different processing techniques. The resultant device characteristics of the PCSS such as breakdown voltage, rise time, and turn-on delay will depend on the actual processing technique that was used for the material. Simulation studies comparing an intrinsic material and a high resistivity SI GaAs PCSS grown through the liquid-encapsulated Czochralski (LEC) process with a deep donor and shallow acceptor compensation mechanism highlight these differences. Simulations also elucidate the role of an n/sup +/-doped layer placed next to the cathode, which increases the breakdown voltage of the device. Extending the n/sup +/ layer length beyond the cathode does not yield further improvement but leads to current confinement along a narrow strip that can initiate local heating or burnout. The doping profile of the n/sup +/ layer also affects hold-off characteristics, a faster gradient ensuring better protection of the cathode against the substrate field, and electron injection. Doping the n/sup +/ region with a higher concentration of carbon impurities does not produce the same effect as doping the n/sup +/-SI interface. These material-related issues are critical to further extending the performance characteristics of PCSSs.

Characterization of a semi-insulating GaAs photoconductive semiconductor switch for ultrawide band high power microwave applications

Simulation results depicting physical conditions in a photoconductive semiconductor switch in the pulse charging state, prior to high power switching, are analyzed. Results show that surface conditions and EL2 traps in semi-insulating GaAs influence the conduction process, specifically at high bias. Formation of trap-filled regions renders the device inhomogeneous for stable conduction and premature breakdown occurs, due to a large extent on unstable current filamentation within the device. Unlike insulators, the breakdown of desorbed gas from the surface (surface flashover) does not contribute to premature breakdown.