Interplay of excitonic radiative recombination and ionization in photocurrent spectra of thick barrier GaAs/AlAs multiple quantum wells

We have studied photocurrent (PC) spectroscopic features of a relatively thick barrier GaAs/AlAs multiple quantum well p-i-n diode at 18K, It is found that the PC spectra do not reflect the photoabsorption spectral lineshape under the low field condition and show negative PC peaks at the exciton resonance wavelengths where the absorption coefficient is maximum. These PC dips are qualitatively explained by considering the distribution of photogenerated carriers and competition between the carrier transport and recombination. A tunneling model calculation is carried out to successfully explain the PC spectral features as well as the field dependence of PC intensity by taking into account the photogenerated carrier distribution and the excitonic absorption lineshape variations with the field.