Contactless evaluation of semi-insulating GaAs wafer resistivity using the time-dependent measurement.

A method based on time-dependent measurement of charge transients has been developed to evaluate the specific resistivity of semi-insulating wafers quickly, non- destructively and with good lateral resolution. The material is inserted between capacitive electrodes. The time-dependent charge distribution after application of a voltage step allows evaluation of the resistivity with high accuracy in the range 10high6- 10high9Omegacm. The technique has been elaborated to allow rapid contactless scanning of wafers for routine measurement of the lateral variation of resistivity with a resolution of about 2 mmhigh2. The results are in agreement with conventional Hall measurements. The mechanical and electronic systems are described in detail. Scans across wafers cut from as-grown as well as annealed ingots are presented.