An efficient and low-cost computer-controlled programmable duty cycle light-emitting diode pulse generator

The decay of photoconductivity from the steady state is widely utilized to characterize semiconductor materials such as hydrogenated amorphous silicon and its related alloys. We propose an efficient and low-cost light-emitting diode (LED) pulse generator with variable duty cycle and intensity to be used in measurements of photoconductivity response time. It is crucial to switch on/off the light swiftly. The circuit developed allows measurements of decay times ranging down to a few hundred nanoseconds. The LED pulse generator was successfully tested in measurements of the temperature dependence of the response time for an a-Si: H film and an a-Si(sub 1-x)C(sub x): H film.