A high sensitivity bridge for the measurement of deep states in semiconductors

The requirements of a capacitance measurement system for the assessment of deep levels in semiconductors are considered. It is concluded that a transformer ratio arm bridge used in the deflection mode operating at 1 MHz with a signal level of a few tens of mV is the most appropriate for high sensitivity measurements. A bridge has been designed which has a good noise performance and this has been used to measure capacitance transients resulting from charge exchange in deep levels where Delta C/C is as low as 10 -6 . The performance is compared with other systems and it is apparent that the bridge provides more than an order of magnitude improvement in sensitivity compared to the most appropriate commercial instruments and a similar improvement on other techniques reported in the scientific literature.