Negative peaks in photocurrent spectra of thick barrier GaAs/AlAs multiple quantum wells

We have experimentally studied photocurrent (PC) spectral features of a relatively thick barrier multiple quantum well (MQW) p-i-n diode at 18 and 80 K as a function of axial electric field. It is found that PC spectra do not always reflect the photoabsorption spectral line shape under the low field condition and show negative peaks at the exciton resonance wavelengths. These PC dips are qualitatively explained by considering the distribution of photogenerated carriers within the intrinsic region and competition between carrier transit and recombination times. Furthermore, the dominance of electron-tunneling transport for the low temperature PC mechanism explains enhanced negative peaks in the PC spectra at 80 K when the tunneling assisted drift is reduced.