Investigations of the n-GaAs-electrolyte interface using time-resolved photoluminescence

Abstract

The time-resolved decay of band-to-band photoluminescence for n-GaAs ( n o = 5 × 10 17 cm −3 and 1 × 10 18 cm −3 ) in contact with aqueous electrolyte was investigated both experimentally (by a sampling technique) and theoretically (by computer simulation) by varying the excitation intensity with an externally applied potential near the point of zero photocurrent under steady state illumination ( −0.5 V (SCE)). The band-to-band luminescence decay was observed experimentally at an excitation wavelength of 636 nm in a range of excitation intensity between 1440 and 0.49 kW cm −2 corresponding to initial excess carrier densities p i between 5.5 × 10 16 and 2 × 10 16 cm −3 . The time behaviour of the luminescence was characterized by a monoexponential least squares fit. A new effect was found concerning the dependence of the decay time on the excitation intensity. There is a maximum of the monoexponential decay time in the range of linear recombination ( p i ⩽n o ) which descends steeply towards high intensities. This maximum can also be found by mathematical simulation. The analysis of the time- and spatially resolved potential, hole and electron density profiles suggests (1) that the occurrence and the shape of the maximum are due to the photocurrent and (2) that it depends on the ratio of the surface recombination and the photocurrent. In the high injection region ( p o >n o ) quadratic recombination dominates the decay kinetics and hence the decay time decreases sharp above p i |n o ≈ 1 .