Self-Powered UV–Near Infrared Photodetector Based on Reduced Graphene Oxide/n-Si Vertical Heterojunction

Reduced graphene oxide (rGO)/n-Si p-n vertical heterojunction is employed in making self-powered photodetector with properties like high sensitivity and fast response time. Efficient transfer of photogenerated charge carriers is allowed via establishing contacts between the semiconductor layers. High sensitivity of the self-powered photo detector is observed in the spectrum of light from 365 to 1200 nm. It is also accompanied by various parameters like high photoresponsivity, fast response and recovery time under illumination of 600 nm. The electric field at the interface of reduced Graphene oxide and n-Silicon results in high photoresponse of the device.

Graphene is well suited for the next generation of optoelectronic devices due to its properties like low light absorbance even in broad spectrum of light, high charge carrier mobility, high current carrying capacity and fast carrier dynamics. Fabrication of graphene includes various approaches like mechanical exfoliation, epitaxial growth and chemical vapour deposition. In order to enhance its properties with high solubility, scalability and cost effectiveness, chemical method is involved to prepare graphene oxide and reduced graphene oxide. The modulation in electrical conductivity and light transmittance of the graphene is achieved by controlling the reduction level and the thickness of reduced graphene oxide film. Zero band gap in graphene is expanded to a relative wide band gap in the reduced graphene oxide making it feasible in the field of optoelectronics. Due to its fascinating properties a study is proposed by authors to investigate the effects of reduced graphene oxide on the self-powered photo detectors.

The characteristics of reduced graphene oxide film were studied using transmission electron microscopy, x-ray diffraction and Raman spectroscopy. X-ray diffraction method showed the reduction in the oxygen containing functional groups of reduced graphene oxides. This in turn increases conductivity and also improves sensitivity of the reduced graphene oxide films. However, to ensure proper band gap, reasonable amount of oxygen containing functional groups are required. Higher the reduction level in graphene oxide higher is the conductivity in the film. This high conductivity shifts the Fermi level further away from vacuum level and also leads to higher built-in electric field. The performance of the photo detectors also rely upon the thickness of the reduced graphene oxide films.

Professor Ting Zhang and colleagues from Suzhou Institute of Nano-Tech and Nano-Bionics, CAS and Professor Yi Wang from C&N Intl. Co. Ltd  in China developed a novel self-powered photo detectors with built-in electric field to meet the properties of an ideal photo detectors such as high sensitivity, fast response and recovery time, zero bias operation, wide spectrum and low fabrication cost. The reduced graphene oxide film not only acts as electron-hole pair generator but also act as hole collector. This minimises the carrier decay that occurs during the transport of photogenerated electrons and holes and acts independently without the need for external power making it highly suitable for micro and nano electronic devices.

The self-powered photo detectors are applicable to various fields such as UV radiation surveillance, flame detection, communication and biomedical imaging.