Computer Simulations of Pulsed-Laser Induced Coherent Plasma Oscillations in GaAs Crystals

Abstract

One-dimensional transport equations for pulsed-laser induced space-charge distributions in GaAs crystals have been computed using a finite difference procedure by two models; (a) Model A for i-GaAs with an applied dc electric field under a uniform illumination over the crystal and (b) Model B for n- and i-GaAs without the electric field under a half illumination to simulate the “transient thermoelectric effect” (TTE). With Model A, the temporal and spatial evolutions of restored space-charge density of photoexcited electrons and holes are obtained, from which an induced electric field is found to oscillate with a single frequency of plasma oscillations (0.3--2, THz), in satisfactory agreement with reported experiments. Model B calculations have revealed that near the boundary between the illuminated and non-illuminated regions, the appreciable enhancement of space-charge densities and induced electric fields are observed, which diffuse or drift toward a positive x direction, showing characteristic damping oscillations with two frequency components f₀ due to the doped donor electrons and f₁ due to the doped and photoexcited electrons of plasma oscillations. Furthermore, the induced TTE voltages measured across both ends of the crystal without dc electric field are simulated to show similar coherent plasma oscillations.