Although amorphous silicon has poorer electronic properties than crystalline silicon, it offers the important technical advantage of being deposited inexpensively and uniformly over a large area. The applications are therefore almost entirely in situations in which either a large device or a large array of devices is needed. The technology which has received the most attention is the photovoltaic solar cell - large scale power production obviously depends on the ability to cover very large areas at a low cost. Input and output devices such as displays, photocopiers and optical scanners also take advantage of the large area capability. Each of these applications requires an electronic device whose size matches the interface with human activity - either a display screen or a sheet of paper - with typical dimensions of 25 cm or larger.

The electronic devices are made up of a few different circuit elements, such as transistors, sensors, light emitting diodes etc. Sections 10.1-10.3 describe how the design of these elements is adapted to the specific properties of a-Si:H. A few of the actual and potential applications are then discussed.

Light sensors

Light sensors made from a-Si: H are either p-i-n or Schottky barrier structures. Unlike crystalline silicon, a p-n junction is ineffective without the undoped layer, because of the high defect density in doped a-Si:H. Illumination creates photoexcited carriers which move to the junction by diffusion or drift in the built-in potential of the depletion layer and are collected by the junction.