The Role of Deep Level Traps in the Optically Controlled

A numerical solution for the transient photoconductivity in the laser-activated bulk semi-insulating GaAs switch has been obtained, in which the influence of EL2 and other traps on the optical generation rates and the recombination rates of free carriers has been determined. Calculated photocurrent pulses are compared with the experimental results of switching measurements under conditions of low laser intensity and low device electric field. The comparison shows that the EL2 model is sufficient to explain the large extrinsic photoconductivity which is observed. The dependence of the recovery on the various traps is discussed. Both the free carrier and trapped carrier concentrations are described by a system of coupled rate equations, which is solved using a fourth-order Runge-Kutta method. The trap parameters used in the rate equations are obtained from recently reported values in the literature. Both analysis and experimental results emphasize the critical role of traps in the design of optically controlled gallium arsenide switches.