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.

Formation of Highly Crystallized β‐PbO Thin Films by Cathodic Electrodeposition of Pb and Its Rapid Oxidation in Air

“…Besides ZnO, electrodeposition of a crystalline oxide thin film of Pb II (PbO) from an aqueous solution of Pb(NO 3 ) 2 has been reported by Zhitomirsky et al [19] PbO has two crystal systems, a (tetragonal) and b (orthorhombic), both of which exhibit n-type semiconductivity, with bandgap energies of 1.9 and 2.7 eV, respectively. [20] The a phase is usually stable at low temperatures, while the b phase is stable at high temperatures or in the presence of trace impurities. Zhitomirsky The process of electrodeposition of b-PbO thin films from aqueous solutions of Pb II salts has been studied in detail.…”

Photo-Seebeck effect in tetragonal PbO single crystals

“…12 Both the polymorphs of the lead monoxide, tetragonal (α-PbO) and orthorhombic (β-PbO) phases, are known to be photoconductive and having indirect band gaps of E g = 1.9 and 2.7 eV, respectively. [12][13][14] In this study, we demonstrate the photo-Seebeck effect in α-PbO single crystals as functions of photon energy and photon flux density. We find that the electrical conductivity increases and the Seebeck coefficient decreases with increasing photon flux density.…”

Laser-assisted deposition of PbO films

“…oxygen, carbon dioxide, water and Ar [3], vacuum sputtering [4] and by exposing Pb films to a radio-frequency oxygen plasma [5]. The thickness of the PbO films deposited by these techniques varies from 3-8nm [5] to 50-70/xm [2]. Films with both crystal modifications have been grown.…”

“…Films with both crystal modifications have been grown. According to Schottmiller [2] and Tompsett and Noble [3] the crystal modification of the deposited films depends on the deposition rate. Kramarenko et al [4] reported that the film crystal structure depends on the substrate temperature; in their experiments the yellow orthorhombic modification has been obtained at room temperature of the substrate and the red tetragonal modification at substrate temperature 200 °C.…”

“…So far lead monoxide thin films have been grown by the following techniques: thermal evaporation in oxygen atmosphere [2], thermal evaporation in presence of various gases, e.g. oxygen, carbon dioxide, water and Ar [3], vacuum sputtering [4] and by exposing Pb films to a radio-frequency oxygen plasma [5].…”