Broadening of gain spectra of quantum-well lasers

Abstract

D. V. Karasyov and V. K. Kononenko UDC 539.293:621.378.35 Key word s: quantum-well heterostructure, semiconductor laser, fluctuations of composition, gain spectra The width and shape of emission bands in semiconductor laser structures depend on the pumping level and the temperature. Broadening of energy levels should also be taken into account. This effect is most pronounced in gain spectra of quantum-well lasers [1 ]. Two main effects of broadening of the levels are considered: heterogeneity of geometrical sizes of quantum wells and finiteness of the time of intraband relaxation of the carriers as regards energy and momentum [2 ]. In the present work a new mechanism of broadening of the spectra of quantum-well lasers due to fluctuations of the composition of solid solutions at the boundaries of the heterojunction is considered [3 ]. The GaAs-AlxGal_x As system is considered as an example. Measurements by high-resolution transmission electron microscopy have revealed substantial heterogeneities of the chemical composition at the boundary of the heterojunction even in optically perfect structures [4 ]. Indeed, according to [5 ], the distribution of the component x in barrier layers of the heterostructure obeys a normal law. Let us consider the effect of this distributution on the energy spectrum of carriers in the quantum well of the GaAs-AlxGa l_xAs system. The effective masses of the carriers in the quantum well are assumed to be equal to those in the barrier layers. Then, for the initial levels of the subbands Ecn with the quantum number n we have approximately [6 ]: