Effect of strain on Auger processes in GaAs and InP based quantum well-lasers - applications for improved threshold current and time response

Abstract

The introduction of biaxial strain to the active region of quantum well lasers creates dramatic changes in the bandstructure of the well. The bandgaps are altered, resulting in an increased wavelength tunability, and the density of states is significantly affected. In particular, the valence band masses can be reduced by a factor of 3 with the introduction of ~2% strain (see Fig. 1).1 As is now well known, this reduced hole mass leads to improved inversion at the bandedge and results in a significantly lower threshold current density for the strained systems2−4; the strain-induced splitting between heavy and light holes also results in an improved selectivity of TE over TM modes in the emission. In addition, it is expected from the threshold conditions for Auger transitions5 that the changes in hole masses and bandgaps associated with strain will greatly reduce the rate of Auger processes in strained materials. This is extremely important for 1.55μm lasers grown on InP, since the Auger transition rate increases exponentially with the small bandgap. In this work we present a comprehensive model of the effect of strain on Auger processes, threshold current density, time response, and polarization dependence of strained quantum well lasers grown on GaAs and InP. We also include the temperature dependence of the Auger rates, threshold current density, and thermionic emission of carriers out of the quantum well; optimization results will be presented for the structure with the lowest threshold current density.