Determining p-n Junction Band Gap

The present chapter describes a new technique for the accurate and reliable determination of p-n diode bandgap energy. The method makes no assumptions about the ideality factor and therefore differs from many experimental techniques. The well-known linear variation of p-n diode terminal voltage with temperature at fixed forward current is still used, but it is shown that if the current through the diode is switched in controlled steps, then it is possible to determine the temperature difference needed to maintain a constant diode terminal voltage. The ideality factor and bandgap can then be accurately determined over a small temperature range at well-defined voltage-temperature points, termed the measurement trajectory. An application is presented using a carefully programmed microcontroller circuit to determine the temperature trajectory for the 1N4148 silicon and OA91 germanium diodes. The microcontroller is being used increasingly in university science laboratories for its availability and simplicity of use [1]. The results show good agreement with the literature values for silicon bandgap energy but give a 30% higher value for germanium.