Carrier-gain dynamics in ${\mathrm{In}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As strained-layer single-quantum-well diode lasers: Comparison of theory and experiment

We present measurements and calculations of femtosecond gain dynamics in ${\mathrm{In}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/${\mathrm{Al}}_{\mathit{y}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{y}}$As strained-layer single-quantum-well diode lasers using a multiple-wavelength pump-probe technique. To aid in the interpretation of gain dynamics induced by both interband absorption and stimulated emission of photons, we develop a detailed theoretical model for gain dynamics in quantum-well laser diode structures and compare it with experimental measurements. In the model, transient gain and differential transmission are computed in a multiband effective-mass model including biaxial strain, valence subband mixing, and polar-optical-phonon scattering both within and between subbands. Transient photogeneration of electron-hole pairs by the pump pulse and subsequent relaxation of carriers by polar-optical-phonon scattering are calculated in a Boltzmann-equation framework.