Low temperature Hall measurements in a cryostat with a built-in magnet

A double AC method is described for measuring the Hall voltage of thin semiconductor samples in the temperature range 4-300 K. The magnetic field is produced inside the cryostat by means of a built-in electromagnet. By this new arrangement fields up to 1 Wb m -2 are achieved at field frequencies of 2 kHz or less. Hall voltages of some 10 nV have been measured. The upper limit of sample resistance is at 10 G Omega . The smallest detectable mobility is of the order of 10 -4 cm 2 V -1 s -1 . Comments are given concerning the proper selection of current frequency and magnetic field frequency. Results of mobility and carrier concentration for a high and a low resistivity sample are given as a function of temperature.