Effects of metal ion chemisorption on gallium arsenide surface recombination: picosecond luminescence decay measurements

Abstract

n-GaAs/KOHSe-/2-(aq) contacts have been studied using real time photoluminescence decay techniques. This system is of interest because metal ion chemisorption improves the steady-state current-voltage properties of GaAs/KOHSe-/*-(aq)/Pt cells, yielding 16% efficiency under simulated 1-sun illumination conditions. In this work, the luminescence decay dynamics of thin epilayer GaAs samples under high level injection conditions were monitored in contact with KOHSe-/2-(aq) solutions. The photoluminescence signals decayed more rapidly after metal ion chemisorption than after a fresh etch, indicating that the metal ion treatment induced a more active recombination and/or charge-transfer process than the etch. A finite-difference simulation was used to model the decays and to extract a minority carrier surface recombination velocity, Smin, for these systems. For etched GaAs surfaces, Smin = 5 X lo3 cm s-I, while GaAs surfaces that had been etched and then exposed to 0.010 M C O ( N H~)~~+ (pH = 11) solutions displayed Smin = 2 X lo5 cm s-l. Qualitatively similar behavior was observed for Rh-, Ru-, and Os-treated GaAs surfaces as well. These data are fully consistent with prior suggestions that the primary effect of metal ion chemisorption is to increase the rate of hole transfer to the Se-/2-(aq) electrolyte, as opposed to decreasing surface recombination processes at the GaAs/liquid contact.

Theoretical and Experimental Upper Bounds on Interfacial Charge-Transfer Rate Constants between Semiconducting Solids and Outer-Sphere Redox Couples

“…Strong adsorption increases the effective surface concentration of acceptor species above that calculated for a random distribution of acceptors, thereby facilitating increased charge-carrier capture rates. Additionally, intermediate capture of charge carriers by surface states prior to subsequent transfer into the acceptor ion, ,, inner-sphere bridges to the redox center from the electrode, and other such processes might also be important in producing very high apparent k et values. , Experiments conducted under such situations do not measure the rate constant for transfer to outer-sphere, nonadsorbed, randomly distributed acceptors at inert semiconductor surfaces, but measure the capture velocity for a fundamentally different charge-transfer process. Adsorption appears to be of concern in a previously investigated system for which real-time luminescence quenching measurements of the charge-carrier decay dynamics had been interpreted as exhibiting k et values larger than theoretically expected , and possibly could affect rate constants for InP/KCl(aq)−Fe(CN) 6 3-/4- contacts in the absence of an oxide overlayer or could establish the upper limit for charge transport through the InP oxide overlayer.…”

Progress in Understanding Electron-Transfer Reactions at Semiconductor/Liquid Interfaces

“…37 The luminescence data obtained by Ryba mainly served to verify that adsorbed metal ions acted primarily as electrocatalysts for minority carrier capture at the solid/liquid interface, as opposed to acting to reduce surface recombination by passivating surface states. 38 The data, however, also yielded evidence for relatively rapid charge carrier quenching at the n-GaAs/KOH-Se -/2contact. The data in Ryba's measurements were obtained under high level injection conditions, so that either electron or hole quenching would produce a reduction in the observed luminescence signal.…”

Reactions of Etched, Single Crystal (111)B-Oriented InP To Produce Functionalized Surfaces with Low Electrical Defect Densities

“…D. Surface Recombination Velocity Measurements. Time-resolved photoluminescence measurements were performed using a time-correlated single-photon-counting apparatus that has been described previously. , Rhodamin 6G (Exciton) was used in the dye laser to provide an excitation at 600 nm. The repitition rate was set to 152 kHz to ensure that the delay between pulses was substantially larger than the time scale for the observed InP luminescence decay (6 ms).…”