Modifications to the Boonton 72BD capacitance meter for deep-level transient spectroscopy applications

Abstract

For accurate determination of the activation energy of a deep-level trap by deep-level transient spectroscopy (DLTS), it is desirable to measure the thermal emission rate over at least two orders of magnitude. Thus, the least time required to acquire DLTS capacitance data over this range will be directly proportional to 100 times the minimum response time of the capacitance meter employed. When an unmodified Boonton 72BD capacitance meter is overloaded by a strong stimulating pulse, erroneous signals caused by the recovery of its overload detection circuitry and 1-MHz amplifier will be superimposed on the first 200 ms of a transient waveform. Therefore, accurate data would require that each transient be captured for times as long as 20 s. In this paper, simple modifications to this instrument are described which significantly improve data-acquisition speed and data quality. This is accomplished by eliminating overload recovery delays and by minimizing noise produced by digital circuitry. Specifically, overload recovery delays are avoided by installing a fast relay which grounds the input of the 1-MHz amplifier during application of the stimulating pulse and by deactivating the internal overload detection circuitry. The noise produced by digital circuitry is reduced by stopping the multiplexing of the light-emitting diode display.