Apparatus for the Measurement of the Hall Effect in Semiconductors of Low Mobility and High Resistivity

An apparatus for the measurement of the Hall effect in materials of low mobility and high resistivity is described. An ac technique is used: The sample is rotated in a static magnetic field at 20 cps, an electric field is applied at 13⅓ cps, and the Hall signal, preamplified by field-effect transistors mounted on the rotating shaft near the sample, is synchronously detected at 33⅓ cps. Hall mobilities as small as 0.2 cm2/Vsec in samples of resistance up to 109 Ω can be measured with negligible detector loading. A discussion is also given of the fundamental limitations of Hall effect measuring equipment. Typical Hall mobilities in iodine single crystals and in iodine complexed 1:1 with poly-n-vinyl carbazole are reported.