Monitoring of state of charge in MOS capacitors by pulsed photocurrent

pulsed illumination of a biased mos capacitor through windowed gates induces a photocurrent which can be used to monitor shifts of bias voltage, in response to a gaseous chemical stimulus. if collimation requirements are relaxed, to allow the use of comparatively simple led light sources, increased window area must be adopted to compensate for the reduced light intensity. experimental and modelled responses demonstrate that useful information may still be obtained, limited by the convolution of response with a finite beam diameter and constrained by window size.