Active layer assessment of AlxGa1-xAsySb1-y/GaSb diode lasers from hydrostatic pressure measurements

Abstract

The threshold current has been measured as a function of pressure up to P=1.3 GPa for double-heterostructure lasers with AlxAsySb1-y active layers (x=0-0.05) lattice-matched to GaSb substrates. Calculations have been performed for x=0 and T=80 K which, in addition to Gamma 6c- Gamma 8v radiative transitions treated by a model including a Gaussian fit to Halperin-Lax band tails and Stern's matrix element, consider other ways of recombination from both the direct Gamma 6c and the indirect L6c conduction band. The results account for the steep rise of the threshold current with pressure, which begins before the direct-to-indirect band-gap crossover at P=1.05 GPa and continues up to P>1.25 GPa, where the lasing ceases, in terms of an essential contribution of the L6c electrons recombining at a rate quadratically dependent on the carrier concentration. The assumption has been borne out in the measurements of the average lifetime of carriers at the threshold. The effect of the Al fraction x in the active layer if T=80 K and that of higher T if x=0 on the threshold current versus the pressure curves are briefly contemplated. It has been shown that, in the given range of x, provided T=80 K, the increase of the threshold current with x can be linearly simulated by pressure supposing dx/dP=2.2*10-10 Pa-1. The scope of such a simulation is discussed. Low-temperature threshold current densities down to 100 A cm-2 have been predicted for lattice-matched AlxGa1-xAsySb1-y/GaSb lasers with an active layer x as high as 0.21.