Intense terahertz pulse-induced impact ionization and electron dynamics in InAs

Electron dynamics and impact ionization are investigated by Monte Carlo method in n-type InAs exposed to intense ultrashort terahertz pulse at 300 K temperature. The sequence of hot electron transfer between the Γ and upper L and X valleys is established: hot electrons of the Γ valley transfer firstly to the L valley, and then they are scattered to the X valley. Electron population in the valleys and characteristic time of their redistribution between the Γ, L and X valleys is investigated in strong electric fields. It is found that the threshold electric field of impact ionization increases with shorter THz pulses. The process of impact ionization is shown to be the dominant energy loss mechanism of hot electrons having energy larger than the threshold energy of impact ionization. Good agreement between the results of calculation and available experimental data is demonstrated.