Optical gain and laser emission in HgCdTe heterostructures

A detailed study of stimulated emission mechanisms as well as laser emission capability has been carried out on Hg1-xCdxTe (0.44<x<0.5) separate-confinement heterostructures grown by molecular beam epitaxy. At low temperature, spontaneous photoluminescence (PL) occurs on extrinsic levels below the gap whereas optical gain exhibits a maximum of stimulated emission shifted towards higher energy, close to the gap. As temperature increases, spontaneous PL is shifted from the extrinsic states to the band-to-band transition by a thermally activated detrapping of the carriers. Above 100 K, spontaneous and stimulated emission vary in a similar way with temperature. Laser emission has been observed up to room temperature for all the heterostructures. The use of quantum wells in the active layer and graded index in the barriers has allowed a significant reduction of the excitation density threshold, as compared to a single separate-confinement heterostructure (SCH) of same composition. However, the high-temperature characteristic temperature T-0 is found to be similar in the two structures. A SCH with a higher energy gap exhibits a more favorable behavior with temperature. These experimental results have been compared to theoretical models. The experimentally observed T-0 can be well simulated by taking into account the Auger effect. From the experimental data, the Auger constant has been determined for each heterostructure. (C) 1995 American Institute of Physics.