The Dependence of Optical Constants on Selenium and Sulphur-Doping in a-Si:H

Abstract

Hydrogenated amorphous silicon–selenium and silicon–sulphur thin films were prepared by the decomposition of SiH4 and H2Se/H2S gas mixtures in an rf plasma glow discharge at a substrate temperature of 230 °C. Optical and electrical measurements show that increasing the selenium content above the gas ratio, H2Se/SiH4 = 10—3, results in an increase in the size of the optical (Tauc) gap and a decrease in the dark conductivity. The band gap of Se‐doped a‐Si:H was found to be between 1.79 and 1.89 eV as the gas ratio (H2Se/SiH4) increased from 10—4 to 10—1 and for S‐doped a‐Si:H lied between 1.80 and 1.96 eV as the gas ratio (H2S/SiH4) increased from 6.8 × 10—7 to 10—4. The refractive index n was calculated from transmission spectra and the value of n was found to decrease with increasing wavelength as well as doping concentration in the wavelength range of 650 to 950 nm. The Urbach energy and defect density were obtained from subgap absorption measurements.

Effect of illumination on hydrogenated amorphous silicon thin films doped with chalcogens

“…The increase in ph and decrease in the activation energy indicate the movement of Fermi level towards the conduction band edge. In comparison of similar doping concentration, that is, H 2 Se/SiH 4 & H 2 S/SiH 4 = 10 À4 , the ph in the Se-doped film was found higher than S-doped films because of lower defect density in the Se-doped films [28]. Fig.…”

“…2. The H 2 Se and H 2 S vapor were mixed with silane gas (SiH 4 ) in order to achieve Se and S doping, respectively [28]. Thickness of the films was measured using Surface Profiler (DekTaK3).…”

Optical properties of Se or S-doped hydrogenated amorphous silicon thin films with annealing temperature and dopant concentration

“…The a-Si,Se:H and a-Si,S:H thin films were prepared in an RF plasma glow discharge (13.56 MHz) using plasma enhanced chemical vapor deposition (PECVD) by the decomposition of H2Se and H2S vapors mixed with silane gas (SiH4) on 7059 corning glass at a substrate deposition temperature of 230 • C, respectively [41,42]. The thicknesses of the films measured by a surface profiler (Dektak stylus-Veeco Instruments Inc.) ranged from 0.24 to 5.44 m. The absence of sharp peaks in the X-ray diffraction (XRD Phillips-Holland Diffractometer, model X pert PRO) patterns confirmed the amorphous nature of the films.…”

“…Lately, Sharma et al have investigated the effect of Se or S doping on a-Si:H and studied the change in conduction mechanism with temperature[40,41]. Use of Se and S as dopants in films grown by capacitively coupled RF glow discharge decomposition of silane (SiH 4 ), hydrogen sulfide (H 2 S) and hydrogen selenide (H 2 Se) diluted in helium (He) results in silicon dangling bonds being terminated in the same way as hydrogen…”