Optically controlled amorphous silicon photosensitive device

Amorphous silicon photovoltaic devices are often fabricated under conditions which lead to a nonuniform electric field in the intrinsic (i) layer including a field-free region at the rear of the cell. The field-free region can contribute a series resistance, especially if the device has been subjected to prolonged optical stress in sunlight. If a continuous blue light source is directed onto such a sample, the dc photocurrent will be strongly impeded by the series resistance. If, however, a weak source of red light which is amplitude modulated (e.g., chopped) is superimposed with the blue light, the resistance of the device will also be modulated. An audio frequency ac photocurrent will appear, in phase with the modulation present in the red light but of much greater amplitude than the red light itself could provide. Thus an optically controlled detector and amplifier is achieved.