Theoretical analysis of profiled quantum-well laser structures

The energy spectrum and transition matrix elements are investigated for a heterostructure laser with an ultra-thin active layer whose thickness is modulated in at least one direction. It is shown that, depending on the depth of the spatial modulation, the density-of-states distribution for such structures has peaks and valleys. This distribution is a transitional case between the spectrum of a one-dimensional quantum well and the spectrum of an array of parallel quantum wires or of a two-dimensional array of quantum dots (in the case of a two-dimensional spatial modulation). Proper choice of the parameters of a profiled structure can result in advantages over the usual quantum-well structure: a peak in the spectrum fixes the laser wavelength and increases the differential gain within a pump-current interval of practical interest, while a valley in the density of states weakens the temperature dependence of the threshold current. The matrix element of the working transitions in a quantum-well structure depends weakly on the quasimomentum in the periodic field, while the forbidden transitions are rather weak compared to the working transitions.