Low-threshold high-T0constricted double heterojunction AlGaAs lasers

Constricted double-heterojunction (CDH) diode lasers of relatively low cw thresholds (28-40 mA) are obtained by growing structures that maximize the amount of current flow into the lasing spot. This is achieved while using "standard" 10-µm-wide oxide-defined stripe contacts. The temperature dependence of threshold currents in CDH lasers with strong lateral mode confinement is found to be significantly milder than for other types of lasers. The threshold-current relative variations with ambient temperature are two to three times less than for any other devices of cw-operation capability. Over the interval 10-70°c the threshold currents fit the empirical exponential law exp ( with T0values in the 240°-375° range To in pulsed operation, and in the 200-310° range in cw operation. The external differential quantum efficiency and the mode far-field pattern near threshold are virtually invariant with temperature. The possible causes of high-To behavior are analyzed, and a new phenomenon--temperature-dependent current focusing--is presented to explain the results.