Many body effects and charge carrier kinetics studied by electro-optical experiments in type-I hetero n- i- p- i structures with selective contacts

Abstract

We report on a comparative study of the electro-optical properties of a tunable two-dimensional electron plasma by transmission, photocurrent (PC), and photoluminescence (PL) measurements. The sheet electron density n (2) in the pseudomorphic strained InGaAs quantum wells of the investigated type-I hetero n- i- p- i structure can be tuned between zero and more than 5·10 12 cm −2 by applying a voltage U pn between the selective and ohmic n- and p-contacts. A direct relation between n (2) and U pn can be determined by capacitance measurements. Many particle effects (bleaching of the exciton, shift of the absorption edge due to bandfilling, renormalization of the bandgap) have been studied as a function of the sheet electron density n (2) in the quantum wells. The carrier dynamics in the type-I hetero n- i- p- i structure was investigated by a detailed comparison of absorption, PL and PC measurements as a function of the applied voltage U pn. A photogenerated hole in the quantum well can either recombine in the quantum well or escape into the p-layers by tunnelling or thermally assisted hopping. The first process is monitored by PL, while the escape process, which varies strongly with the U pn bias dependent potential barrier height and width, contributes to the PC. Both recombination paths are compared with the e- h generation rate determined by the absorption coefficient, which is extracted from transmission experiments.