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A systematic study of the surface of InP annealed under an arsenic pressure is reported. Comparison with data obtained on clean InP and InAs reveal that the surface phosphorus is exchanged with the impinging arsenic down to the two top monolayers, where the reaction stops. Important changes in the surface electronic properties are concurrently observed, especially the shift of the surface states away from the band gap and the decrease of the surface recombination velocity. From both structural and electronic points of view, this object may be seen as bulk InP with an InAs surface fitted on it, and hence, as a first example of a new class of objects, bulk III-V materials with tailored III-V surfaces.

We report the first simultaneous measurements of the photoluminescence yield and of the basic electronic properties (density of states, position of the Fermi level) of InP surfaces subjected to various treatments under ultrahigh vacuum conditions. The surface densities of states located near the band edges are found to govern the surface recombination process. Annealing under As pressure which moves these densities out of the band gap is shown to yield a surface with low surface recombination, in agreeement with this framework.

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Having previously studied the local order of GexSe1-x glasses between pure selenium and x = 1/3, we have now prepared samples for 1/3 ≤ x ≤ 1/2. Glassy materials have been obtained up to x = 0.44 and, at higher x values, the samples are made of GeSe crystallites embedded in a glassy matrix of GexSe1-x, with x = 0.41 ± 0.01, the percentage of glass going to zero when x goes to 1/2. Raman scattering measurements have been performed on a set of such samples, at room temperature. The results lead to the following model of local order : for 1/3 ≤ x ≤ 0.42, the glasses have a GeSe2-like local order with four-coordinated Ge atoms and two-coordinated Se atoms, Se—Se bonds and two Ge—Ge bonds per Ge atom being statistically forbidden; for x ≽ 0.43 strong indications appear for a GeSe-like local order, with both three-coordinated Ge and Se atoms : such a type of coordination has never been previously reported for glasses