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The photoconductive behavior of evaporated layers of lead monoxide in both the tetragonal and orthorhombic crystalline modifications has been investigated. Stoichiometry was controlled on a relative scale by controlling the oxygen pressure during sample preparation, yielding both n- and p-type material. Current—voltage characteristics, optical absorption, and variation of photocurrent with (1) wavelength, (2) applied field, and (3) light intensity are presented and discussed for the two forms. Energy band gaps of 2.0 eV for the tetragonal form and 2.6 eV for the orthorhombic form are indicated. A maximum resistivity of 3×1011Ω·cm with a μτ product of 4×10−7 cm2/V was measured for the tetragonal phase. The corresponding values for the orthorhombic phase were 1×1013Ω·cm and 1×10−9 cm2/V. Whereas in earlier pictures photosensitivity was explained as a contact phenomenon, the present data demand a model such as impurity sensitization or interparticle barrier modulation to explain the observed bulk photosensitivity.

The calcium-strontium phase system has been investigated in the liquid and solid state over the entire range of compositions. The liquidus and_ solidus curves were determined by differential thermal analysis whereas the solid state equilibria were studied by X-ray diffraction methods. Complete miscibility in both the liquid and solid state were observed with a minimum in the liquidus-solidus at 78 ± 2 weight % strontium and at 738°. Calcium, strontium and all calcium-strontium alloys exist in three crystalline modifications, face-centered cubic, hexagonal close-packed and body-centered cubic. There is a minimum in the b.c.c. h.c.p. transition, but the h.c.p. <=* f.c.c. transition in all alloys occurs at temperatures intermediate to the transition temperatures of the pure components. The variation of oo with atomic % at room temperature for f.c.c. alloys is linear in conformity with Vegard's law. At 415°the variation of both Oo and Co of the h.c.p. modification is linear with atomic per cent, for the calcium rich alloys; however, positive deviation from Vegard's law occurs with strontium-rich alloys. Positive deviation from Vegard's law also occurs in the strontium-rich b.c.c. alloys (615°).

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Coevaporation with vapor quenching has been used to combine metallic and nonmetallic elem.ents into new vitreous semiconductors. These binary glasses, formed with an excess of nonmetal over. a wide ran.ge of compositions exhibit semiconducting and optical properties differing from the correspondmg proper~Ies of either component alone or of any known crystalline compound formed between the comp.onents. Detal~e? investigation of the vitreous Bi-Se system indicates that an inten;ne?iate temperature :el?~n of the equilibrium phase diagram has been retained at room temperatU1:e. VanatIon of ban~¥aI?' resls~lv~ty, and phootosensitivity with composition are presented and interpreted m tenns of the eqUilibnum eXlstmg at ",620 C.

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The infrared photodetecting properties of new vitreous Bi–Se films are described. Such films are prepared by coevaporation and vapor quenching. A room-temperature D* value of 2×1011 cm/W·sec1/2 was measured at the peak sensitivity wavelength (∼1 μ) for an optimum composition film. Response times range between 0.3 and 3 msec. In addition, measurements were made of D* as a function of sample composition, incident photon flux, and temperature.