Quantum kinetics of semiconductor light emission and lasing

Semiconductor light emission is analyzed as a paradigm of a nonequilibrium quantum mechanical many-body problem. The medium excitations and the quantized light field inside and outside a semiconductor slab are treated consistently. Splitting the photon density of states into a medium and a vacuum induced contribution the arbitrarily strong semiconductor emission is described as spontaneous emission into the vacuum induced part. With increasing gain narrowing peaks of growing intensity evolve for each propagation direction, whereas under laser conditions one propagation direction is favored by the cavity.