Amorphous photocoupler consisting of a-SiC:H thin film light emitting diode and a-SiGe:H thin film photodiode

Hydrogenated amorphous silicon germanium (a-SiGe:H) thin films having the optical energy gap between 1.4–1.6 eV were prepared by the plasma enhanced chemical vapor deposition (PECVD) method. The photoconductivity of the a-SiGe:H increased from (2.1±0.5)×10−7 to (1.1±0.5)×10−5 S/cm by increasing the flow rate of hydrogen gas as well as increasing the substrate temperature from 190°C to 250°C. The a-SiGe:H was applied to the carrier generating layer in an infrared light film photodiode. The film photodiode has the structure of glass/indium tin oxide/SnO2/ p-a-SiC:H/i-a-SiGe:H/n-μc-Si:H/Al. The a-SiGe:H photodiodes can be operated at room temperature and have a greater response to infrared light from 700 to 900 nm wavelength than that of the conventional a-Si:H photodiode. Furthermore, the a-SiGe:H photodiodes are applied as the photodetector in an amorphous photocoupler in which the small optical energy gap of a-SiC:H thin film light emitting diode (TFLED) is the light emitting device.