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

Abstract

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.