Time-resolved photoluminescence studies of metal ion treated n-GaAs in electrolytes

Citation

Ryba, Gail Naomi (1993) Time-resolved photoluminescence studies of metal ion treated n-GaAs in electrolytes. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/mzj0-sz79. https://resolver.caltech.edu/CaltechTHESIS:01102013-103203745

Abstract

Using the technique of time-correlated photon counting, the time-resolved photoluminescence response of n-type gallium arsenide (n-GaAs) in contact with aqueous KOH – Se^2- - Se2^(2-) electrolytes was monitored before and after exposure to aqueous 0.010 M solutions of ruthenium, cobalt and osmium ions. Cobalt ions caused the rate of carrier loss from the GaAs to increase relative to that for untreated samples, as evidenced by faster decays. It was inferred that hole and/or electron transfer to the selenide redox species was catalyzed by the cobalt ions.

A model incorporating ambipolar diffusion, bulk trapping, radiative bimolecular recombination, surface trapping and surface charge transfer and employing a finite-difference algorithm was applied to the photoluminescence decays. Under high intensity illumination, the photoluminescence decays from the gallium arsenide samples with aluminum gallium arsenide overlayers could be fit using the expression for bimolecular kinetics, indicating that radiative recombination dominated the decays in these samples.

For the samples immersed in aqueous KOH – Se^(2-) – Se_2^(2-) solutions, with and without chemisorbed metal ions, a time-dependent increase in the GaAs photoluminescence indicated that changes occurred at the surface during the course of the experiment Prior to metal ion treatment, the lifetime in KOH - Se^(2-) – Se_2^(2-) solutions stabilized at about 3.7 ns, which could be fit with an effective surface hole capture rate constant of 5.1x10^3 cm/sec. After cobalt ion treatment photoluminescence decays with 1/e lifetimes on the order of 0.6 ns were measured and, if it is assumed that surface hole capture dominated the decay, correspond to a surface hole capture rate constant of 1.7x10^5 cm/sec. The 1/e lifetimes for ruthenium and osmium treated surfaces were never observed to be less than 1.5 ns and quickly returned to the 3.7 ns lifetimes observed prior to metal ion treatment It is inferred that the cobalt treated surface is more chemically inert under illumination than either ruthenium or osmium treated surfaces.

Preliminary measurements for GaAs immersed in acetonitrile with and without dimethylferrocene and dimethylferrocenium indicated that the rates of carrier loss at the surface are much higher than they are for the aqueous selenide redox species, even in the absence of the redox species. However, small increases in rate of loss were discernible after addition of redox couple to the acetonitrile, and further work is warranted.

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