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The effects of transient and steady-state illumination on the electrical properties of single-crystal cuprous oxide have been investigated in the temperature range from 230 to -20°C. For samples equilibrated well within the region of Cu,O stability, conduction was governed by an acceptor level at 0.4 eV above the valence band as determined from the temperature dependence of the Hall effect. The presence of two minority carrier trapping levels was also established and trapping parameters were determined from an analysis of the transient photoconductivity. The 0.4-eV acceptor level was also found to be present in a sample equilibrated under conditions placing its composition in a region near the CuO-Cu,O phase boundary. For this sample, however, only a single deeper trapping level was observed. A third type of sample, equilibrated under conditions which placed its composition in a region near the Cu-Cu,O phase boundary, was characterized by both a high hole density and a high mobility with an acceptor level energy of 0.16 eV. Also, the presence of two effects, the thermal quenching of the steacly-state photoconductivity and its nonlinear dependence on light intensity, were shown to be consistent with the presence of deep traps in this material.

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Large area single crystals of Cu2O were grown by the process of high temperature annealing. Cu2O was prepared in finely polycrystalline form by the complete oxidation of Cu plate in air at temperatures of 1020°C to 1050°C. Subsequent annealing of the polycrystalline plates at higher temperatures allowed secondary recrystallization to occur. Single-crystal grains having surface areas larger than 1 in.2 were grown consistently on Cu2O plates having thicknesses of 0.010 in. to 0.060 in. In some cases, entire polycrystalline plates were transformed into single crystals, and as a result, individual single crystals having surface areas of 3 in.2 and larger were obtained. The annealing temperature and the annealing time were found to depend markedly on the plate thickness. Thick plates required lower temperatures and longer annealing times than the thinner plates. X-ray analysis of the large grains verified that they were single crystals without excess strain, and indicated preferred orientation, with the (211) and (311) planes predominating. Resistance profile measurements at room temperature on quenched samples showed that a variation in resistance exists through the thickness of the plate.

A great number of bands have been observed by light scattering and infrared absorption in Cu,O crystals corresponding to transitions most of which are normally forbidden in the perfect crystal. An analysis of the symmetry properties of the lattice modes in the presence of defects is given. I n particular the role of each symmetry site for the defects is investigated and the observed modes interpreted as being due to activated band modes and localized modes. Double phonon processes are observed as well as the normally allowed optical transitions for the perfect crystal.Un grand nombre de bandes sont observbes par diffusion de la lumibre et absorption infrarouge dans d u Cu,O correspondant t i des transitions pour la plupart interdites dans le cristal parfait. Une analyse des propribtbs de symktrie des modes du rbseau en presence de dkfauts est donnbe. E n particulier le role de chaque site de symktrie pour le d6faut est Btudie et les modes observes sont interpret& comme &ant diis h des modes de bande actives par les dkfauts ou a des modes localisks. Des processus A deux phonons sont observes aussi bien que les transitions normalement permises pour le cristal parfait.