Study of broadened waveguides in gallium indium arsenide antimonide/aluminum gallium arsenic antimonide quantum well lasers

The goal of this research is to improve the performance of GaInAsSb/AlGaAsSb quantum well lasers operating at ∼2 mum by incorporating thick waveguide regions. Previous researchers have shown a significant improvement in the slope efficiency of GaInAsSb/AlGaAsSb lasers by increasing the waveguide core thickness. These thick waveguides decrease free carrier absorption in the highly doped cladding regions. Further broadening of the waveguide core to 2--4 mum results in a decrease of the optical confinement factor, Gamma, with the gain region that could have additional benefits to laser performance that have not been analyzed yet. It is predicted that by reducing Gamma, filamentation should be inhibited resulting in improved beam quality. Additionally, the wider emitting aperture in the transverse direction should yield a lower beam divergence.;Key to the success of these thick waveguide structures is the injection efficiency, etainj. Electrons and holes are injected across a relatively large region and have a greater chance of recombining in the waveguide before they reach the quantum wells. Therefore, carrier transit time and recombination time in the waveguide will determine how well the device will perform. Injection efficiency also directly affects filamentation gain, and therefore beam quality. This study is the first to examine the affect of waveguide thickness on efficiency, carrier transport, and beam quality in electrically injected devices.;Multiple quantum well GaInAsSb/AlGaAsSb lasers with varying waveguide core thicknesses are characterized. The predicted improvement in beam quality is not seen. Simply minimizing Gamma is not effective for these electrically injected devices due to the corresponding decrease in etainj. Future work could focus on improving the carrier lifetimes using indirect bandgap barrier material such as AlGaAsSb with >40% Al composition to improve injection efficiency. Temperature performance of the thick waveguide laser is also examined. Spectral data show an atypical blue shift with increased current under pulsed conditions for waveguide core thicknesses of 3 and 4 mum. The blue shift is caused by the reduced Gamma and etainj that leads to large threshold current densities and an appreciable "band filling" effect.