Development of thin film photocoupler consisting of amorphous silicon carbide light emitting diode and amorphous silicon germanium photodiode

Abstract

Amorphous thin film photocouplers consisting of amorphous silicon carbide (a-SiC:H) thin film light emitting diodes and amorphous silicon germanium (a-SiGe:H) thin film photodiodes and photoresistors have been developed. The amorphous photocouplers are designed for operation in the infrared regions. The a-SiGe:H thin films were prepared by the glow discharge plasma CVD method from the gas mixture of silane (SiH4) and germane (GeH4). The research started from the installation of GeH4 gas line system, followed by the optimizations of preparation conditions for obtaining high photo-conductivity undoped a-SiGe:H films. The results showed that the optical energy gap of a-SiGe:H decreased when the flow rate of GeH4 increased, and the optimal substrate temperature was about 250 ํC. It was also found that the dilution of hydrogen gas (H2) with an appropriate flow rate was another important factor to obtain high photo-conductivity a-SiGe:H. In the work, a-SiGe:H having high photo-conductivity (10 -6 - 10 -4 S/cm) and small optical energy gaps of 1.4-1.6 eV were prepared. The amorphous p-i-n junction photodiodes, using the a-SiGe:H as active layers, were fabricated and had good responses to the infrared light. The developed a-SiGe:H thin film photodiodes were applied as the light detectors in the amorphous photocouplers. The results showed that the photocouplers could be operated in the infrared light (wavelength 100-900 nanometer). The amorphous photocouplers have potentials to be used in various electronics applications; for examples, measurement of material sizes, optical communication, and optoelectronics, etc.