The III-IV compounds, i.e. those made from elements in groups III to V in the periodic table, such as gallium (Ga), indium (In), phosphorous (P), antimony (Sb) and arsenic (As), are used widely in the electronics and optoelectronics industries and are attracting growing interest from the sensor community.

While some existing magnetoresistors are based on materials such as InAs and InSb, high sensitivity Hall effect sensor have been fabricated from III-IV compounds including GaAlAs, InP, GaAs, InAlAs and InGaAs. The major sensor characteristics are defined by their material and shape and vary according to , the electron mobility, and E _g, the energy band gap: sensitivity rises with an increase in and the thermal characteristics improve at higher values of E _g. A small UK company, AHS Ltd, which arose from research at UMIST, is now using these compounds in unique 2-DEG sensing structures. The company has exploited the band gap engineering concept in the design of many of its sensors. MBE (molecular beam epitaxy) is used to deposit semiconductors such as GaAs as very thin films (~10-20nm) between two slightly thicker materials with a larger energy band gap. This results in a quantum well which is able to trap electrons in fixed quantum energy states; a so-called two-dimensional electron gas (2-DEG), a term that refers to the electrons confinement in two dimensions rather than being able to roam freely in the semiconductor as in conventional Hall sensors. This gives rise to...