Grain boundary effect in polycrystalline InP films from optical reflectance measurements

Abstract

Polycrystalline InP films were deposited by d.c. magnetron sputtering of an InP target on glass substrates. The effect of inter-crystalline barrier on the carrier transport in InP films has been studied critically. The grain boundary potential, the density of trap states at the boundary region and the carrier concentration in the films were obtained by utilizing an optical technique, developed on the basis of the Dow-Redfield model. The roughness (30–40 nm) of the surface of the film was determined by measuring the diffuse reflectance by a spectrophotometer while the band gap (~1.35 eV) was determined from the transmittance versus wavelength traces. The barrier height in InP films was found to be in the range 0.16 to 0.22 eV, while the corresponding density of trap states in the grain boundary region was ~0.3–7.0 × 10 12cm −2. It was observed that the experimental plot of normalised absorption coefficient below the band gap showed excellent agreement with the theoretical model based on the consideration of both the electric field and the mechanical stress to be present in the film.