The devices reported in Applied Physics Letters have a wide spectral detection range of 1000nm to 400nm (covering pretty much the visible spectrum up to infrared). The device uses a graphene layer as the top transparent electrode, also acting as an efficient collection layer for photo-generated carriers. The ZnO layer in between the graphene and Si layers acts as an antireflection layer that traps the incident light and enhance the light absorption, the researchers explain.
The built-in electric field at both graphene/ZnO and ZnO/Si interfaces enhances the charge separation of photo-generated electron and hole pairs and as a result, the sensitivity and response time of the device is significantly improved compared to graphene-silicon heterojunction devices.
By selecting appropriate band alignment and unique properties of different materials, the researchers managed to design a device with good sensitivity and a fast response time from the near UV to the infrared region. Turn-on response time was around 280μs for the experimental prototype, but the Taiwanese team expects this could be reduced to under 100μs
Because the self-powered photodetector has a simple architecture following a Si compatible fabrication process, they hope it could find many use cases in ultra-low power applications, including next generation optoelectronic devices.
Read the full article paper at: http://scitation.aip.org/content/aip/journal/apl/109/5/10.1063/1.4960357;jsessionid=JtScanfko5aNAkb29MIr5Egc.x-aip-live-02#f1