Influence of the Plasma Regime on the Structural, Optical, Electrical and Morphological Properties of a-Si:H Thin Films

摘要

In this work we report how it is possible to control the plasma regime near the substrate surface, from predominantly α to predominantly γ', passing trough and intermediate α-γ' regime, and simultaneously control the energy of the ions striking the substrate during a-Si:H deposition from a silane glow discharge in a modified triode type PECVD reactor. To do so, we apply a DC voltage (V_(pol)) to a set of grids placed in front of the r.f. electrode and by doing this, we control the energy of the ions striking the substrate during the film's growth and the plasma regime near the substrate. Under a plasma of the γ' regime, the surface roughness is high and the films are poorly compact. In the α-γ' regime, the ion bombardment is moderate and the films are highly smooth and compact. In the a regime the ion bombardment is higher and so the films can become more compact but the surface roughness increases and the electrical properties deteriorate. The results achieved show that the best transport properties are achieved for the films deposited in the α-γ' regime corresponding to a V_(pol) of 38 V. Under this condition the films presented a dark conductivity, σ_d = 6.2xl0~(-12)(Ωcm)~(-1), activation energy, ΔE≈0.9 eV, hydrogen content, C_H = 9%, factor of microstructure R = 0.085, photosensitivity, S = 2xl0~7, and an optical gap E_(op)≈1.77 eV).