Lasers for large modulation bandwidth and low-threshold applications

Carrier transport and recombination dynamics are seen to be the intrinsic limitations to the performance of quantum well lasers. The carrier relaxation times as a function of quantum well width were measured in laser structures using a streak camera. Auger recombination rates were experimentally determined in compressively strained In x Ga 1-x As/InGaAsP/InP quantum wells from the large signal modulation of single mode lasers. In order to overcome the intrinsic limitations in present semiconductor laser designs, a new device concept has been demonstrated: the tunneling injection quantum well laser, in which the carriers are injected into the active lasing subband by resonant and sequential tunneling. The highest 3 dB modulation bandwidth (12.5 GHz) and the highest differential gain (6 X 10 -16 cm 2 ) for a single quantum well laser have already been demonstrated. To realize threshold currents of much less than 1 mA, quantum wire lasers are required. We present theoretical and experimental results on the performance characteristics of quantum wire lasers. The experimental structures are being realized in the In x Ga 1-x As/GaAs system by MBE growth and regrowth and electron beam lithography.