Investigation of the a-Si:H films by using thermal and light-induced annealing treatment in atomic hydrogen atmosphere in H-W-ECR CVD system

Abstract

To investigate the stability of hydrogenated amorphous silicon (a-Si:H) films, the thermal and light-induced annealing treatment in an atomic hydrogen atmosphere (TLAH) is carried out by using a new hot-wire-assisted microwave electron-cyclotron-resonance chemical vapour deposition system (H-W-ECR CVD) modified from a conventional microwave electronic cyclotron resonance chemical vapor deposition system (MWECR CVD). In order to compare with the TLAH method, the experiments of thermal annealing and thermal and light-induced annealing are also performed. Meanwhile, for the purpose of analysing the photoconductivity degradation quantitative, the photoconductivity degradation is assumed to obey the extended exponential law: 1/σph=1/σs-(1/σs-1/σ0)exp[−(t/τ)β], where the extended exponential β and the time constant τ are gained by the slope and the intercept of the line according to the linear relationship between ln (−ln ((σs−1−σph−1)/(σs−1−σ0−1))) and ln t, deduced from the extended exponential law; the photoconductivity saturation value σs can be obtained by Gaussian fitting according to the relationship between photoconductivity and light-soaking time in the logarithmic coordinate system. The experimental results show that the TLAH can improve the stability, microstructure and opto-electronic properties of the annealed a-Si:H films, obviously decrease their optical band gaps and remarkably move their photoluminescence spectrum (PL) peaks toward low energies.