Physics of semiconductor lasers

We recall the various advances which have made possible the modern semiconductor laser with its outstanding performances. Although it already gained several orders of magnitude improvement in such parameters as the threshold current density or modulation speed, we are still not yet anywhere near the physical limits of operation, and quite often these have not yet been determined. We compare the two approaches to ultimate performances, namely the use of quantum boxes in active layers and the microcavity-laser structure. We show that the latter appears more promising, as it makes the best use of the Boson nature of photons, whereas the former is handicapped by the Fermion nature of electrons which severely limits the use of single quantum box systems in optoelectronic applications. In the microcavity approach, the two possibilities of pillar-type or photonic-bandgap material-based structures are described. Besides leading to the threshold-less laser with squeezed-photon number, low-noise emission, such structures would also strongly improve the performance of other light-emitting devices.