Temperature-induced single-to-double branch transformation of operating characteristics in semiconductor lasers with a low-dimensional active region

The temperature behavior of operating characteristics in semiconductor lasers with a quantum-confined active region is studied with a proper account for (i) non-instantaneous capture of charge carriers from the waveguide region into the active region and (ii) internal optical loss that depends on the carrier densities. Because of (i), the carrier densities are not pinned in the lasing mode, i.e., they are functions of the injection current. In view of (ii) and as a result of pump-currentdependence of the carrier densities, so becomes the internal loss coefficient. This in turn leads to the roll-over of the light-current characteristic at high currents (i.e., decreasing optical power with increasing injection current) and, under certain conditions, appearance of the second branch in it. The laser characteristics are shown to transform qualitatively with varying temperature: they are conventional, i.e., consist of one branch, at low temperatures but they have two branches, i.e., are of a binary nature, at high temperatures. The two branches merge together at the maximum operating current beyond which the lasing quenches. In contrast to the first (conventional) lasing threshold, the threshold for emerging the second branch decreases with increasing temperature. The pump-current-dependence of the carrier densities and internal loss coefficient is also fascinating: these quantities decrease with increasing current in their second branches.