Bound-free intersubband absorption in p-type doped semiconductor 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. Example calculations in GaAs/${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As quantum wells indicate that bound-free absorption may dominate over bound-bound absorption in the wavelength 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-hole contribution being an order of magnitude lower. Calculated results show very good agreement with experimental measurements [K. M. S. V. Bandara et al., Phys. Rev. B 48, 7999 (1993)].