Photoelectric properties of amorphous and crystalline films of antimony

Abstract

Thin films of antimony occur in amorphous and crystalline forms. For the thinnest films the amorphous phase is stable; at a critical thickness (corresponding to an optical transmission of about 30%) the film crystallizes spontaneously. The phase change has been detected by studying the variation of photoelectric emission with thickness for antimony films evaporated at pressures less than 5 × 10−8 Torr. At the transition there is an abrupt increase of about an order of magnitude in the photoelectric yield. A sudden decrease in the electrical resistance of the film, previously taken as an indication of the phase transition, occurs at a rather greater film thickness. It is suggested that the thinnest films are made up of islands of amorphous antimony; at the critical thickness crystallization occurs but the island structure is still retained. The decrease in resistance at greater thicknesses is probably due to coalescence of the islands. The photoelectric threshold of crystalline films of antimony thicker than about 15 nm is constant at (4.52 ± 0.01) eV. In the crystalline region the results are a good fit to the Fowler analysis. In the amorphous region the yield Y may be related to the photon energy h v by the empirical relation Y ∼ ∼ (h v — h v0)3, which has been found to apply to a number of semiconductors. Amorphous films have a threshold in the region of 4.7 eV.