Photovoltaic study of the substrate-layer interface for Sn-doped GaAs grown by metalorganic vapor phase epitaxy

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Abstract
Photovoltaic spectra have been obtained for Sn-doped GaAs epitaxial layers grown by metal-organic vapor phase epitaxy (MOVPE) on Cr-doped semi-insulating GaAs substrates with a view to studying the substrate-layer interface characteristics. The photoresponse was found to be relatively strong and extended into the near infrared to λ≂2 μm. The photosignal is due to carrier excitation at the interface, where a high density of deep traps creates a depletion region and a potential barrier. The shape of the spectral response can be analyzed to yield information on the nature of these traps. They are found to be EL2 and Cr-related electron and hole traps in concentrations which depend on the layer growth conditions. The barrier height deduced directly from the spectra is about 0.6 eV, and is attributed to Fermi level pinning at the Cr2+ electron trap level.