Light absorption and IR photodetectors in P-doped quantum wells

A procedure is proposed for calculating the light absorption due to transitions from bound to free hole states in semiconductor quantum wells. The continuum spectrum is described via the scattering states approach. In calculating the transition matrix elements account is taken of the position dependence of Luttinger parameters. It is shown that in symmetric structures it suffices to calculate the wave functions of only one block of the Luttinger-Kohn Hamiltonian. Example calculations in GaAs/AlGaAs quantum wells indicate that bound-free absorption may dominate over bound-bound absorption in the wave length range of interest for practical applications. It is also found that the position of the absorption peak is essentially influenced by states with nonzero transverse wave vector, due to the high nonparabolicity of the valence band dispersion. This implies that energies of virtual states in the continuum cannot be simply deduced from the absorption profile. Transitions from the heavy hole ground state to continuum give the principal contribution to absorption, the light holes contribution being an order of magnitude lower. Bound-free absorption is also calculated in strained InGaAs/GaAs p-doped quantum wells for various values of the mole fraction x. Values of absorption exceeding those in unstrained GaAs/AlGaAs structure by at least a factor of 2 are found. Calculated results show very good agreement with experimental measurements.