Optical refrigeration of GaAs: Theoretical study

We have performed a theoretical analysis of laser cooling (i.e., cooling via luminescence up-conversion) of bulk GaAs based on a microscopic many-particle theory of absorption and luminescence of a partially ionized electron-hole plasma. This theory allows us to model the semiconductor over a wide range of densities and for temperatures from the few-Kelvin regime to above room temperature. In this paper, we analyze in detail how various physical processes help or hinder cooling. We show that at high temperatures (T >= 300 K), cooling is limited by Auger recombination. As temperature is lowered to about 200 K, band filling as well as excitonic effects become significant. Phase-space filling hinders cooling but is overcompensated by excitonic effects, which are found to be beneficial for cooling. At very low temperatures (<= 30 K), parasitic background absorption limits cooling, and the interplay between excitonic absorption line shapes and parasitic background absorption determines whether or not cooling is possible in this temperature regime.