EXCITON-TRANSITIONS IN INGAAS/INP QUANTUM-WELLS INVESTIGATED BY PHOTOCURRENT SPECTROSCOPY

A detailed analysis of the exciton resonances dominating the intersubband transitions of InGaAs/InP multi-quantum wells grown by chemical beam epitaxy is presented. Pin diodes with a mesa structure, containing several quantum wells within the intrinsic region, were investigated. Photocurrent spectra were detected as a function of temperature and the exciton peaks HH-E(1), LH-E(1) and HH-E(2), identified by a comparison with calculations, were observed up to room temperature. Full bleaching of the exciton features, induced by exciton localization effects, was reached at low temperature. In agreement with optical absorption data, the temperature dependence of the exciton peaks was studied by lineshape fitting: a homogeneous broadening contribution ascribed to the interaction with LO phonons was found. Capacitance-voltage measurements at Variable temperature (10-300 K) were performed: the temperature dependence of the space charge region width and impurity density profile was studied. The photocurrent corresponding to the (n = 1) heavy hole to electron exciton transition (HH-E(1)) was measured as a function of the reverse bias, temperature and illumination intensity. At zero bias, strong thermal activation of the photocurrent was measured, while, as a function of the reverse bias, some shoulders were observed in the low-temperature characteristics. Thermionic emission over the barriers and phonon-assisted tunnelling were identified as the dominant contributions to the perpendicular transport of photoexcited carriers.