A method of observation of interface states for ultra-thin insulating layer/semiconductor interfaces was developed by use of X-ray photo-electron microscopy measurements under bias. The analysis of the energy shift of the semiconductor core level as a function of the bias voltage gives energy distribution of interface states. When the atomic density of SiO2 layers was low (e.g., SiO2 layers formed at 350C), only one interface state peak was observed near the mid-gap, and it was attributed to isolated Si dangling bonds at the interface. For SiO2 layers with a high atomic density (e.g., SiO2 layers formed at 700C), on the other hand, two interface state peaks, one above and the other below the mid-gap, were observed, and they were attributed to Si dangling bonds interacting weakly with a Si or oxygen atom in SiO2. Interface states could be passivated by cyanide treatment which simply involved the immersion in cyanide solutions such as KCN and HCN solutions. When the cyanide treatment was applied to |indium tin oxide/SiO2/mat-textured single crystalline Si| metal-oxide-semiconductor (MOS) solar cells, the photovoltage was greatly increased, leading to a high conversion efficiency of 16.2%. When the cyanide treatment was performed on polycrystalline Si (poly-Si)-based MOS diodes, a greater effect in comparison to that for single crystalline Si-based MOS diodes was observed due to the elimination of defect states in poly-Si as well as Si/SiO2 interface states. The cyanide treatment could also increase the conversion efficiency of pn-junction single crystalline and poly-Si solar cells.

Methods of Observation and Elimination of Semiconductor Defect States. H.Kobayashi, Y.L.Liu, Y.Yamashita, J.Ivánčo, S.Imai, M.Takahashi: Solar Energy, 2006, 80[6], 645-52