Intervalence Band Absorption and Carrier Heating in Type-II Sb-Based Lasers

摘要

The intervalence absorption in InAs/InGaSb/InAs type-Il 4 micrometers 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 absorption process (IVA) was resolved from that of the interband gain dynamics. The IVA absorption occurs at in-plane momentum k11 approximately 0.O25 Angstrom(exp-1) 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 N(exp 0.17) was deduced reflecting the enhancement of the electron hole wavefunction 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 the IVA resonance enhanced nonradiative Auger recombination transitions at higher temperatures. Thermal diffusion times of the order of approximately 100 micrometers that increases with temperature were measured.