Tunneling competition of photoexcited carriers in a system of monolithically integrated dual multiple InGaAs/AlGaAs and GaAs/AlGaAs quantum wells

Vertical transport of photoexcited carriers has been studied in a p–i–n diode whose intrinsic layer contains two different multiple quantum wells (MQW), GaAs/Al0.15Ga0.85As (MQW1) and strained In0.15Ga0.85As/Al0.15Ga0.85As (MQW2) isolated by a thick Al0.15Ga0.85As barrier. Pseudo-negative photocurrent (PC) peaks are observed at exciton resonance wavelengths of MQW1 located far from the n-electrode under low electric fields, while the normal positive excitonic peaks recover with increasing the electric field. Moreover, the PC intensity of MQW1 as a function of inverse electric field shows linear dependence due to Fowler–Nordheim-type tunneling with a slope change. The observed PC intensity crossover is rigorously explained by tunneling probability calculations, because of differences in the thickness and height of the transport limiting tunneling barriers, assuming dominance of electron tunneling transport for the PC responses.