Photoconductivity in InGaAs/InP quantum well heterostructures-inter-sub-band and sub-band-continuum transitions

The authors consider the photoconductive response of undoped and modulation-doped multi-quantum-well heterostructures of InGaAs/InP. Optical transitions between confined sub-band levels, between sub-bands and extended miniband states, as well as fundamental band-gap transitions are identified and studied as a function of temperature T. The photoconductivity generally shows a phase reversal and vanishing amplitude in the approximately=100 K range. The photoconductivity signal in all samples is negative at low T. This is the result of Coulomb scattering of the finite equilibrium number of electrons in the well, when photoexcited holes appear in the well. Contacts are shown to greatly influence the response. Their influence is studied by comparing with contact less, radio frequency measurements. By identifying excitations to the minibands at the quantum well edge energies they determine the band offsets. Sub-band energies are calculated and compared with the experimental values.