Measurement of Carrier Lifetime and Absorption Recovery Time in Reverse-Biased GaAs/AlGaAs Single Quantum Well Laser Structures with Optical Pulse Mixing

We describe an optical pulse mixing experiment with a two-segment GaAs/AlGaAs single quantum well, graded-index separate confinement heterostructure laser to determine the effective lifetime of photogenerated carriers in a short reverse-biased segment with subpicosecond resolution. This lifetime is of importance if such
a segment is used as a fast photodetector or as a saturable absorber in a monolithic mode-locked laser structure. We found that the lifetime depends not only on the applied bias but also on the excitation pulse energy. Lifetimes shorter than 5 ps have been observed. The strong dependence on excitation pulse energy is attributed to screening effects of the escaped carriers. A simple model based on an exact solution of the one-dimensional Schroedinger equation for a particle in a quantum well in an electric field together with an electrical equivalent circuit verifies this assumption.