Carrier dynamics and optical properties of gallium arsenide- and indium phosphide-based strained quantum well lasers.

Abstract

As material quality and processing techniques continue to improve over the years, the performance of optoelectronic devices using multiple quantum wells has reached the point where intrinsic material characteristics, such as carrier transport, recombination lifetime, etc., are expected to be important issues. These intrinsic characteristics have been investigated with respect to laser and modulator structures. Carrier transport was investigated in AlGaAs/GaAs and InGaAs/InAlAs modulator structures using an all-optical time-of-flight technique, allowing temporal resolution of $\sim$1 ps. The observed fast transport times can only be explained by a field-dependent carrier emission out of the quantum well, after which transport through the continuum states can occur. The carrier relaxation processes to the quantum well, including the carrier diffusion, capture into the quantum well and relaxation in the well, have been studied. If the electron-hole (e-h) recombination time by stimulated emission for a laser at high injection approaches these relaxation times, the carrier distribution in the quantum well can be "hot" and is not described by a quasi Fermi distribution. This creates serious limitations for the laser performance by introducing gain-compression enhanced Auger rates and other hot-carrier related effects. These Auger recombination rates have been measured in compressively strained In$\sb{x}$Ga$\sb{1-x}$As/InGaAsP/InP quantum wells for the first time. The Auger recombination rates were derived from the measured turn-on delay times during large-signal modulation of single mode lasers. A new device concept has been demonstrated to overcome these intrinsic processes. In this device, termed the tunneling injection quantum well laser, carriers are transported to the active lasing subband by resonant and sequential tunneling. Record performance compared to other single quantum well lasers has been demonstrated in terms of differential gain and modulation bandwidth, showing the potential for this new device.