Photoconductivity in Tetragonal and Orthorhombic Lead Monoxide Layers

Abstract

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.