On Feasibility of Population Inversion Between the Quantum Confinement Levels in Quantum Wells Under Interband Photoexcitation

We discuss a possibility of achieving population inversion and the associated generation of stimulated terahertz radiation employing transitions between the quantum confinement energy levels of electrons in GaAs/AlGaAs quantum wells under interband photoexcitation. The population inversion occurs between two bottom levels in the conduction band according to a four-level scheme under nonstationary conditions during excitation of electrons from valence band to the top electron state and rapid population of the lower energy level due to processes with the emission of LO-phonons. The time of the depletion of this level due to relatively slow downward energy transitions with the emission of acoustic phonons determines the time interval for the existence of the population inversion, which can amount up to several hundred picoseconds. During this time, the generation of stimulated terahertz radiation is possible at transitions between the two bottom energy levels of electrons in the quantum well.