Photocoupler consisting of light-emitting diode and SnO2-Si /n on p+/ junction device

A photothyristor with S-type negative resistance was formed by evaporating a transparent SnO2 electrode onto an Si epitaxial wafer (n on p+) covered with thin SiO2 film. The breakover voltage of the photothyristor is very sensitive to illumination; the wavelength of maxium sensitivity is 0.75 micron. This photothyristor has been combined with a commercial LED to form a photocoupler which can be used as a photosensitive phase shifter (with switch-on time of 25 nsec controlled by photodiode current), a photosensitive triac, and a photosensitive pulse oscillator (with repetition frequency controlled by photodiode current). It is found that In2O3 can be used in place of SnO2 for the transparent electrodes.