A capacitance meter of high absolute sensitivity suitable for scanning DLTS application

A new type of capacitance meter is developed that is designed to measure lowest capacitance changes of space charge structures in semiconductors. It is especially suitable for carrying out scanning DLTS experiments because here not the usually given relative sensitivity but the absolute sensitivity of the measurement is important. From principal considerations an optimum bridge circuit configuration is derived allowing very high sensitivity. The bridge is a resonance-tuned LC bridge working at 28 MHz in deflection mode with automatic slow zero bridge balance during the measurement. For a 2 pF sample and a 100 mV applied ac signal at an integration time constant of 1 s a correlator DLTS system with this bridge gives a noise level equivalent to an initial capacitance change of 6 × 10−7 pF, corresponding to only 60 excited atoms. It is shown that this value in principle can be further improved.