Theory of low temperature capacitance measurements on amorphous silicon thin film solar cells

A theory of low temperature capacitance measurements on thin film amorphous silicon structures, like p-i Schottky diodes or p-i-n solar cells, is presented. As the interface effects and the glow discharge deposition process dramatically affect the intimate structure of thin film materials, the material properties of thin films are extremely different from the material properties of thick layers. The theory takes into account the effect of the finite dimensions of the semiconductor layers in order to explain the experimental results. A small signal approximation leads to a simple analytical expression of the capacitance which can be easily used for measurement fitting. An extensive analysis of parameter sensitivity is presented together with some examples of how experimental results can be interpreted. To date, low temperature capacitance measurements appear to be the first characterization technique of thin doped layers included in a thin film structure.