35-kV GaAs subnanosecond photoconductive switches

Abstract

Abstruct-Photoconductive switches are one of the few devices that allow the generation of high-voltage electrical pulses with subnanosecond rise time. We are exploring high-voltage, fast-pulse generation using GaAs photoconductive switches. We have been able to generate 35-kV pulses with rise times as short as 135 ps using 5-mm gap switches and have achieved electric field hold-off of greater than 100 kV/cm. We have also been able to generate an approximately 500-ps FWHM onloff electrical pulse with an amplitude of approximately 3 kV using neutron-irradiated GaAs having short carrier life times. This paper describes our experimental results and discusses fabrication of switches and the diagnostics used to measure these fast signals. We also describe our experience with the nonlinear lock-on and avalanche modes of operation observed in GaAs.

Voltage pulse forming dynamics in a transmission line section employing photoconductive charging and discharging

“…Fig. 7 shows the results as predicted by the computer model using the 50 picosecond transit time, and with both gap recovery functions given by (6) with time constants and yielded a reduction in the amplitude. As delay was increased beyond 750 picoseconds, the peak height did not change, but the exponential tail decreased in height.…”

“…Various devices have been demonstrated for pulse-forming applications over a broad range of voltage levels and pulsewidths [ 11- [6]. Other charged line applications include microwave burst generation by frozen wave structures [7], and by use of the line section as a resonator [8].…”

Photoconductive switch design for microwave applications

“…Note that the nonlinear lock-on avalanche phenomenon [5,6], which has greatly reduced optical energy requirements, is to be avoided here because it significantly reduces the breakdown field of the device and cannot be turned off in the picosecond time frames needed for steady-state GHz operation. In most of the simulations described here, the triggering light intensity is high enough to cause the electric field in the switch to rapidly fall below the 3.0 to 5.0 kV/cm required for avalanche lock-on to occur.…”

<title>Monte Carlo modeling of solid state photoswitches</title>

“…A current of density J flows and two transverse etectromagnetic (TEM) pulses with electric field E and magnetic field B propagate outward, so that the residual electric field on the GaAs slab is E0 -E. From Ampere's law, using symmetry, B=?. !Jd (1) Gaussian cgs units are used here, c denotes the speed of light, for ThM propagation E=B, and edge effects are neglected. The current density is J=enevd (2) where e is the magnitude of the electron charge, e the conduction electron density and Vdis the drift velocity.…”