Excitonic effects in the photoconductivity of quantum-well GaxIn1-xAs/InP structures

The photoconductivity spectra of quantum-well structures consisting of 50 alternating 7 to 12-mm-thick GaxIn1-xAs (x=0.47) layers forming quantum wells and 10 to 15-nm-thick InP barriers have been investigated. Characteristic excitonic peaks 11H, 11L, 13H, 22H, and 22L were observed in the high-quality structures. A strong temperature dependence was found for the 11H exciton, while no such dependence was observed for any of the other excitons. This is explained by the fact that the 11H state of an exciton falls in the range of energies which are forbidden for free carriers, while the remaining states are resonance states and overlap with the continuous spectrum. The thermal activation energy of photoconductivity was found to be 150+/-30 meV, much greater than the exciton binding energy and close to the depth of the potential well for electrons. This shows that the photosensitivity is due to above-barrier charge-carrier transfer and that the tunneling transfer between the wells is negligible. (C) 1997 American Institute of Physics.