Intervalence band absorption and carrier heating in type-II Sb-based lasers

The intervalence absorption in InAs∕InGaSb∕InAs type-II 4μm quantum well laser structure was investigated using band-edge nonlinear pump-probe spectroscopy techniques where two pump beams chopped at different frequencies are used to excite the sample. The spectrally resolved probe nonlinearity is measured at the sum frequency. Given their different characteristic nonlinearities, the contribution of the intervalence band absorption process (IVA) was resolved from that of the interband gain dynamics. The IVA absorption occurs at in-plane momentum k‖∼0.025Å and is not resonant with the interband lasing energy, therefore does not compete with the interband transition at low temperature and low carrier densities. A density dependent interband transition matrix element of N0.17 was deduced reflecting the enhancement of the electron hole wave function overlap due to the space-charge fields in the type-II wells. Significant lattice heating observed above 80K is reflected in the growth of an out of phase slow signal, resulting from the reduction of lattice thermal conductivity and a possible IVA resonance enhanced nonradiative Auger recombination transitions at higher temperatures. Thermal diffusion times of the order of ∼100μs that increases with temperature were measured.