1.5μm quantum dot laser material with high temperature stability of threshold current density and external differential efficiency

Abstract

Self-organized InAs quantum dot (QD) lasers based on InP substrate were grown by means of solid source molecular beam epitaxy (SSMBE). Six InAs QD layers with high dot density and highly uniform dot sizes were used as active medium. Broad area (BA) and ridge waveguide (RWG) lasers with different cavity lengths were processed and characterized. Also the influence of a post-growth rapid thermal annealing (RTA) process on the laser characteristics was investigated. The lasers showed a high modal gain of 12 - 14.5 cm-1 per dot layer and a threshold current density for infinite cavity length of 120 A/cm2 per dot layer. In pulsed operation, as-cleaved BA lasers with a cavity length of 292 μm can be operated up to 120 °C. High characteristic temperature values were obtained with T0 = 125 K (20 °C to 45 °C) and T0 = 100 K up to 120 °C. The slope efficiency of about 0.28 W/A can be kept constant over a wide operating temperature range of up to 100 °C. Mounted RWG lasers with 388 μm cavity length and operated in pulsed mode showed a maximum output power of 120 mW a slope efficiency of 0.42 W/A at 15 °C. The lasers can be operated at 150 °C with 25 mW output power. These results demonstrate very well the temperature insensitive lasing performance expected in nearly ideal QD lasers due to the high density of states localized at the transition energy, which allow a very robust ground state lasing.