Investigation of the amorphous to microcrystalline phase transition of thin film prepared by electron cyclotron resonance chemical vapor deposition method

Hydrogenated silicon (Si:H) thin film growth by hydrogen dilution method and its phase transition were investigated in an electron cyclotron resonance chemical vapor deposition (ECR-CVD) system. These amorphous and microcrystalline structured silicon thin films were deposited on glass and silicon substrates. The structure, optical and electrical properties of these films were identified by Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, scanning electron microscope (SEM), UV-visible spectroscopy, and dark/photo conductivity measurements. The dilution ratio (H₂/SiH₄) was varied to obtain different qualities of silicon thin films and we found that a phase transition from amorphous to microcrystalline could be obtained when dilution ratio (H₂/SiH₄) is above 0.71. These films with lower microstructure parameter (R*=0.07) and hydrogen content (C_H=18%) have low optical gap (1.85), and exhibit the highest photo conductivity (Ã_ph) of 2.2E-5Ω^-1cm^-1 and lowest dark conductivity (Ã_d) of 1E-9Ω^-1cm^-1 at the phase transition boundary. Due to proper atomic hydrogen could break the weaker SiSi and SiH bonds to form the rigid structure, and then the lower microstructure parameter and hydrogen content could be achieved. The lower hydrogen content in films makes the optical gap to be lower for absorbing more photons which is the reason why there is a better photo response at the phase transition boundary. Furthermore, high-quality hydrogenated silicon thin films are realized through the diluted control of both silane and hydrogen flow rates. Finally, we demonstrate that high quality intrinsic hydrogenated silicon thin films deposited with high growth rate (~1nm/s) using ECR-CVD, are suitable as absorber in a-Si solar cells.