Properties of semiconductors useful for sensors

Different types of solid state sensors demand different basic properties of the semiconductor materials from which they are made. The best transistor material is not necessarily the best material for a certain sensor. One must choose a semiconductor for a particular sensor on the basis of its fundamental properties, such as energy band structure. For example, piezoresistance sensors are made of silicon or germanium mainly because a large effect occurs only in semiconductors, such as these, having complex band edge structures. On the other hand, an intrinsic infrared photon detector requires an energy gap Egcorresponding to the longest wavelength λmto be detected, [Eg(eV)=1/λm(µm)] as well as a direct gap. Compatibility with integrated circuitry may sometimes be a consideration also. A review is given of the materials requirements of effects and devices useful in solid state sensing, and of the present state of development of semiconductors important for sensor applications. Materials discussed include Si, Ge, III-V compounds, II-VI compounds, IV-VI compounds, and others. Problems and prospects for future development are indicated.