Semiconductor Quantum Well Lasers With a Temperature-Insensitive Threshold Current

This paper proposes and demonstrates a new multiquantum well (MQW) laser structure with a temperature-insensitive threshold current and output power. Normally, the mechanisms that cause the threshold current (I_th) of semiconductor lasers to increase with increasing temperature T (thermal broadening of the gain spectrum, thermally activated carrier escape, Auger recombination, and intervalence band absorption) act together to cause I_th to increase as T increases. However, in the design presented here, carriers thermally released from some of the QWs are fed to the other QWs so that these mechanisms compensate rather than augment one another. The idea is in principle applicable to a range of materials systems, structures, and operating wavelengths. We have demonstrated the effect for the first time in 1.5 μm GaInAsP/InP Fabry-Perot cavity edge-emitting lasers. The results showed that it is possible to keep the threshold current constant over a temperature range of about 100 K and that the absolute temperature over which the plateau occurred could be adjusted easily by redesigning the quantum wells and the barriers between them. TEM studies of the structures combined with measurements of the electroluminescent intensities from the wells are presented and explain well the observed effects.