Improved electrical properties in nanocrystalline Si formed by metal induced growth

In recent work, the electrical properties of metal-induced-grown (MIG) Si thin films were studied by using current-voltage (I-V) data from a metal/Si Schottky contact. It was found that controlling the doping level of the films and annealing in forming gas (15% H₂ and 85% N₂) can improve the quality of the nc-Si films. From SIMS analysis on the nc-Si film deposited from a highly doped target, the nc-Si can duplicate the doping level of the sputtering target. Study of p-type doped nc-Si films showed that the fabrication of Schottky diodes on nc-Si films made from an extremely high-doped target (∼10²⁰ cm^-3) or low-doped target (∼10 ¹⁵ cm^-3) was not successful. For highly doped p-type films, tunneling causes Ohmic conduction instead of rectifying conduction. For the nc-Si film deposited from a low-doped p-type target, the film shows conversion to n-type characteristics when measured by a hot probe. This might be due to defects or oxygen in the film. N-type films at the middle doping level (∼10¹⁷ cm^-3) gave good Schottky diodes after annealing the film in forming gas at 700°C. The Schottky diodes fabricated by high work-function metal (Au) gave the rectifying ratio of ∼10 ³. Several techniques, e.g. slow/fast two-step sputtering at low working pressure and surface polishing, were used to improve the photo response of Schottky photodiodes. The open-circuit voltage (V_oc) of 0.164V and short-circuit current density (J_sc) of 2.5 mA/cm² were achieved under 100mW/cm² illumination.