Photocurrent spectra of monolithically integrated dual multiple quantum wells

Abstract

We have experimentally studied the vertical transport mechanism of photoexcited carriers in a p-i-n diode whose intrinsic layer contains two different quantum wells, GaAs/AlGaAs (MQW1) and InGaAs/AlGaAs (MQW2) isolated by a thick barrier by photocurrent (PC) spectroscopy. When the MQW2 layer located near the n-type substrate is illuminated from the n-side at wavelength below the GaAs band gap, the PC signal is more enhanced at the exciton resonances than the p-side illumination. For the MQW1 layer, on the other hand, pseudonegative PC peaks are observed at the exciton resonance wavelengths under low electric fields, while the normal positive excitonic peaks recover with increasing the electric field. These results are rigorously explained by considering that electron tunneling transport is dominant and that the transport from MQW1 to the n-electrode through MQW2 is blocked by the central thick barrier at low fields because shadowing effects of the front MQW1 layer decrease the number of photons absorbed in the MQW2 layer at the MQW1 resonances.