Study of cyclotron-resonance-induced conductivity inn-GaAs

Abstract

A study has been made of the change in the conductivity of $n$-GaAs under cyclotron-resonance (CR) conditions (cross modulation) at high magnetic fields. Measurements are presented of CR-induced Hall effect, CR-induced conductivity, and the CR absorption coefficient in $n$-GaAs, as a function of temperature (8-40 K) at three magnetic field values ($B=6.3, 10.5, \mathrm{and} 13.0$ T). The CR-induced Hall-effect measurements show that the change in the conductivity under CR conditions is due to a change in the free-carrier density for $B=10.5 \mathrm{and} 13.0$ T over the entire temperature range and for $B=6.3$ T below 15 K. For $B=6.3$ T above 15 K a decrease in the mobility is observed. The change in the free-carrier density is calculated with a three-level rate equation model. With this model the energy relaxation time of the photoexcited carrier can be calculated from the measured change in the conductivity and the absorption coefficient. This results in an energy relaxation time with a ${T}^{\ensuremath{-}3}$ temperature dependence and times of the order of ${10}^{\ensuremath{-}8}$ s. Using this temperature dependence of energy relaxation time, the CR-induced conductivity change is quantitatively explained. The energy relaxation of the photoexcited carriers is discussed. It is believed to be a two-step process involving a quasielastic transition from the first to the zeroth Landau level followed by a subsequent relaxation to the bottom of the band by the emission of acoustical phonons. The measured energy relaxation time combined with the measured momentum relaxation time derived from the CR linewidth and from dc transport measurement shows that electron scattering in high magnetic fields is a highly elastic process. The number of interactions per unit time in which energy is transferred to the number of interactions in which only momentum is transferred varies from ${10}^{\ensuremath{-}3}$ at 40 K to ${10}^{\ensuremath{-}5}$ at 10 K.