Increase of temperature and crystallinity during electrical switching in microcrystalline silicon

We investigate electrical stressing and switching in hydrogenated microcrystalline silicon (µc-Si:H) by thermal, and optical and electrical measurements of Cr/µc-Si:H/metal thin-film structures. Boron-doped microcrystalline Si films of 30-50 nm thick are deposited by hotwire chemical vapor deposition (HWCVD) on Cr-coated glass at 160°C and contacted with Ag or Al. Switching in devices of size 5 to 30 µm is stimulated by a current-ramp from 10 nA to 50 mA. We find that the voltage across the µc-Si:H devices initially increases logarithmically with current, then saturates at 2~3 V, and finally drops to a low value of 1 to 1.5 V. This drop indicates a permanent decrease of device resistance to below 1 kΩ. During current stressing, the surface temperature increases with the bias current, and the surface reflectivity changes. After switching, a small increase in crystalline fraction can be observed by micro-Raman scattering measurements. The observations suggest electrothermal processes which cause changes in microstructure of the µc-Si bulk during current stress.