Optimisation of the RF power density to obtain good quality hydrogenated amorphous silicon films in a home-made glow discharge system

A set of hydrogenated amorphous silicon (a-Si:H) films were prepared in a home-made chemical vapour deposition (CVD) system by varying, 20 MHz RF power density from 20 to 130 mW/cm(2) to find the optimised value of the RF power density. The other deposition parameters such as substrate temperature, T-s, total chamber pressure, P, silane (SiH4) gas flow rate and deposition time were kept constant at values 300 degreesC, 200 mTorr, 12 sccm and 4 h, respectively. Films were characterised by constant photocurrent method, darkconductivity, photoconductivity, and optical transmission measurements. The best film is deposited at the power density of 69 mW/cm(2) and it has a deep defect density, Nd = 2.3 x 10(15) cm(-3), an optical gap, E-g(Tauc) = 1.69 eV, a thickness, d = 3.49 mum, an Urbach parameter, E-0 = 54 meV and a photocarrier mobility-lifetime product mutau = 2.1 x 10(-5) cm(2)/V. We have also studied the influence of deep defect density and structural disorder on the magnitude of steady-state photoconductivity. (C) 2003 Elsevier B.V. All rights reserved.