Kinetics of persistent photoconductivity in ${\mathrm{Al}}_{0.3}$${\mathrm{Ga}}_{0.7}$As and ${\mathrm{Zn}}_{0.3}$${\mathrm{Cd}}_{0.7}$Se semiconductor alloys

The kinetics of persistent photoconductivity (PPC) in ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As and ${\mathrm{Zn}}_{0.3}$ ${\mathrm{Cd}}_{0.7}$Se has been investigated. The PPC relaxation behaviors in both materials can be well described by stretched-exponential functions, ${\mathit{I}}_{\mathrm{PPC}}$(t)=${\mathit{I}}_{\mathrm{PPC}}$(0)exp[-(t/τ${)}^{\mathrm{\beta }}$] (β<1). For ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As, the relaxation-time constant τ, as a function of the relative photoexcited electron concentration n, is measured through the variation of the excitation photon dose in the temperature region T≥10 K. At low temperatures, we found that in ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As, τ decreases and reaches a minimum value as n increases in the low-concentration region but it increases with increasing n in the higher-concentration region. Such a turning-over behavior observed in ${\mathrm{Al}}_{0.3}$ ${\mathrm{Ga}}_{0.7}$As is believed to be due to the crossover from a nondegenerate to a degenerate regime as the electron concentration increases.