Electronic properties of amorphous phosphorus prepared by chemical transport in a glow discharge

Abstract

Amorphous films of phosphorus, between 3 and 20 μm thick, have been prepared by chemical transport in a low-pressure hydrogen plasma. The conductivity of a number of specimens with different metal electrodes was measured in vacuo as a function of temperature between room temperature and 450 K. After desorption of moisture on the specimen surface, room temperature conductivities between 10⁻¹² and 10⁻¹⁵ Ω⁻¹ cm⁻¹ are observed; activation energies lie between 0.9 and 1.1 eV and pre-exponential factors between 200 and 1000 Ω^−l cm⁻¹. The spectral dependence of the photoconductivity shows a sharp onset of the response at 1.1 eV and leads to estimates of between 2.5 and 3 eV for the optical gap. On the basis of the results it is suggested that transport takes place in extended states.