Temperature dependence of photoresponse in p-type ${\mathrm{G}\mathrm{a}\mathrm{A}\mathrm{s}/\mathrm{A}\mathrm{l}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}$ multiple quantum wells: Theory and experiment

Bound-to-continuum (BC) absorption and photoresponse in p-type quantum well infrared photodetectors are investigated theoretically and experimentally as a function of polarization and temperature. Using the $8\times 8$ envelope-function approximation model, the quantum well electronic structure and wave functions are calculated and then the BC absorption curves are obtained on an absolute scale as a function of photon energy, light polarization, and temperature. Since optimum absorption obtains for structures with the second light-hole (LH2) state at the top of the well, a nonoptimized long-wavelength infrared structure and an optimized mid-wavelength infrared structure were grown by molecular-beam epitaxy and their characteristics measured to test the theory. Whereas the optimized sample has the LH2 resonance at the top of the well, the nonoptimized sample has light-hole quasibound states within the heavy-hole continuum. This different placement of the light-hole states produces a different temperature and polarization dependence of the absorption process in these samples. Our temperature-dependent photoresponse measurements corroborate most of the theoretical findings with respect to the long-wavelength threshold, shape, and polarization and temperature dependence of the spectra.