Polycrystalline and amorphous semiconductors

This chapter discusses two important applications of non-single crystal semiconductors: photovoltaic solar cells and large screen liquid crystal display. The electrical and optical properties of polycrystalline and amorphous semiconductors are described. Grain boundaries play a major role in determining the behaviour of polycrystalline materials, acting as energy barriers to current flow and as trapping centres for minority carriers. Grain size and doping levels work together with barrier heights to control material properties. Amorphous materials are characterised by lack of order, but can...

This chapter discusses two important applications of non-single crystal semiconductors: photovoltaic solar cells and large screen liquid crystal display. The electrical and optical properties of polycrystalline and amorphous semiconductors are described. Grain boundaries play a major role in determining the behaviour of polycrystalline materials, acting as energy barriers to current flow and as trapping centres for minority carriers. Grain size and doping levels work together with barrier heights to control material properties. Amorphous materials are characterised by lack of order, but can function as semiconductors with low carrier mobilities. Amorphous silicon, containing hydrogen (aSi:H) is used to make thin film transistors, acting as switches at each pixel point in a LCTV display, thus facilitating matrix addressing. It is also used to make cheap solar cells. Crystalline silicon dominates the commercial field of PV solar cells, but is under challenge from a number of polycrystalline materials, such as CdS:CuInSe.