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 T0 parameter of a heuristic exponential law. This T0 parameter has a value of about 80 K in Al(x)Ga(1-x)As heterostructures with a direct fundamental gap, while it is rather large (300 K) in indirect-gap Al(x)Ga(1-x)As. Samples with an AlAs mole fraction (here x = 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 T0 parameter. As a direct consequence of the differential T0 values, indirect-gap Al0.46Ga0.54As has a room-temperature threshold comparable to the standard laser material Al0.33Ga0.77As.