EFFECTS OF METAL-ION CHEMISORPTION ON GAAS SURFACE RECOMBINATION - PICOSECOND LUMINESCENCE DECAY MEASUREMENTS

n-GaAs/KOH-Se--/2-(aq) contacts have been studied using real time phot oluminescence decay techniques. This system is of interest because met al ion chemisorption improves the steady-state current-voltage propert ies of GaAs/KOH-Se--/2-(aq)/Pt cells, yielding 16% efficiency under si mulated 1-sun illumination conditions. In this work, the luminescence decay dynamics of thin epilayer GaAs samples under high level injectio n conditions were monitored in contact with KOH-Se--/2-(aq) solutions. The photoluminescence signals decayed more rapidly after metal ion ch emisorption than after a fresh etch, indicating that the metal ion tre atment induced a more active recombination and/or charge-transfer proc ess than the etch. A finite-difference simulation was used to model th e decays and to extract a minority carrier surface recombination veloc ity, S-min, for these systems. For etched GaAs surfaces, S-min = 5 x 1 0(3) cm s(-1), while GaAs surfaces that had been etched and then expos ed to 0.010 M Co(NH3)(6)(3+) (pH = 11) solutions displayed S-min = 2 X 10(5) cm s(-1). Qualitatively similar behavior was observed for Rh-, Ru-, and Os-treated GaAs surfaces as well. These data are fully consis tent with prior suggestions that the primary effect of metal ion chemi sorption is to increase the rate of hole transfer to the Se--/2-(aq) e lectrolyte, as opposed to decreasing surface recombination processes a t the GaAs/liquid contact.