We describe a new time-resolved probe of excited electronic states near surfaces of semiconductors, as applied to cleaved crystals of ZnTe. Electrons photoexcited to the conduction band by a 5-ps laser pulse are re-excited by a second pulse to states above vacuum energy. Analysis of the photoelectrons resulting from this resonant two-photon process yields data on energy distributions and relaxation times of electrons in the intermediate states. Preliminary evidence for persistent (∠150 ps) occupation of states up to 1.6 eV above the conduction band minimum in ZnTe is presented.
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Williams et al. (1982) studied this question.
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