Indirect-to-direct transition of stimulated emission in AlxGa1-xAs.

The sensitivity of the threshold for stimulated emission on temperature is typically described by the tsub0 parameter of a heuristic exponential law. This Tsub0 parameter has a value of about 80 K in AlxGa1-xAs heterostructures with a direct fundamental gap, while it is rather large (300 K) in indirect-gap AlxGa1-xAs. Samples with an AlAs mole fraction (here x equal 0.43 and 0.44) close to the direct-to-indirect crossover change the nature of their fundamental gap, and thus the dominant channel for stimulated emission, from indirect to direct with rising lattice temperature. This temperature-induced change in bandstructure is reflected in a drastic change of the Tsub0 parameter. As a direct consequence of the differential Tsub0 values, indirect-gap Al0.46Ga0.54As has a room-temperature threshold comparable to the standard laser material Al0.33Ga0.77As.