Sensitive Recording Alternating-Current Hall Effect Apparatus

An apparatus is described which will measure mobilities of the order of 10−2 cm2/volt sec in semiconductors. It is especially suited for measuring Hall voltage in samples of very low conductivity—as low as 10−11 ohm−1 cm−1. This sensitivity is achieved by use of a magnetic field which is automatically reversed every six seconds, an oscillator of frequency 24 cps, and an ac amplifier and phase sensitive detector with a recorder output. Such an arrangement lends itself to quick independent testing of the component units and easier interpretation of unusual experimental results. A novel feature is the use of an Amplidyne control circuit for regulation of the magnet current and reduction of the time required to reverse the magnetic field.