Visualization of the transition from 2d to 3d and from non-k-conservation to k-conservation in the lineshapes of quantum wells and true superlattices

Abstract

Clear experimental and theoretical evidence is presented that k is not conserved and does not need to be conserved when excitons recombine at low temperatures in GaAs quantum wells and superlattices. This surprising effect is due to thermalization and thus localisation of excitons in potential fluctuations. Increasing temperature as well as increasing coupling of wells is found to reestablish the well known k-conservation rule. A complete lineshape theory of excitonic and free electron-hole recombination processes enables one to describe all limiting cases: The spontaneous emission profile for uncoupled and coupled wells from 1.5 K up to room temperature. The 300 K lineshapes of uncoupled and weakly coupled wells are dominated by excitonic emission.