Microcomputer controlled C-V plotting in semiconductor devices

The teaching of semiconductor physics and semiconductor devices can be enhanced by simple experiments carried out on commercially available devices, for example investigations of the I-V characteristics of a diode. A technique which is widely used for determining the impurity concentrations at p-n junctions is to measure the capacitance of a reverse biassed diode as a function of bias voltages: this is known as a C-V plot (e.g. Hilibrand and Gold 1960). The behaviour of real devices is far from straightforward. The author has run a C-V plotting experiment at Liverpool Polytechnic for a number of years. It seemed an experiment which lent itself to the computer collection of data, with subsequent rapid analysis and graphical display on the TV screen. The article describes how, using a BBC microcomputer, this has been achieved.