Possible origin of large response times and ambipolar diffusion lengths in hot-wire-CVD silicon films

We measured the response time tau(R) and the ambipolar diffusion length L-amb in amorphous (a-Si:H) and microcrystalline silicon films (mu c-Si:H) prepared by hot-wire chemical vapor deposition (KW-CVD). The response times in the amorphous and microcrystalline HW films were larger by factors of 100 and 1000, respectively, than in standard PE-CVD a-Si:H films (1-2 mu s). The ambipolar diffusion length of the HW-CVD films was about twice as large as in conventional glow-discharge films. Strong doping of microcrystalline HW films with trimethylboron (TMB) led to a reduction of the response time. The results hint to a positive effect of the compact microstructure of HW-CVD films. We suggest the dark conductivity activation energy, E-act, and response time, tau(R), to be used as suitable parameters to describe optoelectronic film properties.