Influence of surface morphology of the polycrystalline silicon on field electron emission

摘要

Electron field emission from polycrystalline silicon films has been investigated. The polycrystalline silicon was deposited by LP CVD. Polysilicon layers were in situ and diffusion doped with POCL_3 at 900, 950 °C for 30 min. Sharpening of asperities on polysilicon layer surface was performed by thermal oxidation in dry O_2 or H_2O at different temperatures in the range 900 to 1100 °C. After oxidation and removing of the oxide the surface of polycrystalline silicon has developed asperities, especially in case of oxidation at lower temperature. The asperities on polysilicon surfaces have special irregularities, i.e. different sizes (height-base ratio) and shapes. The surface morphology was estimated by scanning electron microscope (SEM). The measurement of emission current from samples was performed in a high vacuum system, which could be pumped to stable pressure of 10~(-6) Torr. The emission areas and local field enhancement factors have been determined and used to establish a relationship among current-voltage curves for polycrystalline silicon with different surface morphology. The polycrystalline silicon layers are characterized by a relatively high emission current. This is connected with large emission area.