MANY-BODY EFFECTS AND CHARGE-CARRIER KINETICS STUDIED BY ELECTROOPTICAL EXPERIMENTS IN TYPE-I HETERO N-I-P-I STRUCTURES WITH SELECTIVE CONTACTS

We report on a comparative study of the electro-optical properties of a tunable two-dimensional electron plasma by transmission, photocurren t (PC), and photoluminescence (PL) measurements. The sheet electron de nsity n((2)) in the pseudomorphic strained InGaAs quantum wells of the investigated type-I hetero n-i-p-i structure can be tuned between zer o and more than 5 . 10(12) cm(-2) by applying a voltage U-pn between t he selective and ohmic n- and p-contacts. A direct relation between n( (2)) and U-pn can be determined by capacitance measurements. Many part icle effects (bleaching of the exciton, shift of the absorption edge d ue to bandfilling, renormalization of the bandgap) have been studied a s 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 inve stigated by a detailed comparison of absorption, PL and PC measurement s 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 in to the p-layers by tunnelling or thermally assisted hopping. The first process is monitored by FL, while the escape process, which varies st rongly with the U-pn bias dependent potential barrier height and width , contributes to the PC. Both recombination paths are compared with th e e-h generation rate determined by the absorption coefficient, which is extracted from transmission experiments.