Researchers at IIT-Madras have developed an alternative to the silicon photodetector, which is a major component in modern appliances. A nanoscale photodetector developed by IIT-Madras has higher energy efficiency compared to existing materials.

A photodetector or photosensor converts light radiation into an electrical signal, which results in excess charge carriers. They are used in applications ranging from high-tech night vision equipment, camera, optical spectroscopy systems and optical communications to everyday appliances such as automatic door opening systems, barcode readers and intelligent lighting systems.

Prof Somnath C Roy, Department of Physics, who led the research, says they have "demonstrated a device made from a common oxide material that is highly stable and versatile and achieves excellent response to a wide-spectrum of light because of unique core-shell nanostructure-based design".

The geometry of nanowires makes them efficient for light detection. Nanowires are crystalline wires whose diameter is one-thousandth that of human hair.

The higher surface-to-volume ratio and short channel length of the nanowire devices make them more photo-sensitive than the larger bulk photodetectors made from the same materials. Different kinds of nanowires detect different types of light sources; the detector developed at IIT-Madras can identify ultraviolet (harmful to human tissue) and visible light.

The device was fabricated via single-step photolithography comprising a cupric oxide and cuprous oxide core-shell architecture - that is, cupric oxide nanowire as the inner core and the cuprous oxide nanoparticles layer as the outer shell.

The electrical contacts are taken from the outer cuprous oxide shell. When light falls on this single nanowire device, charges are generated in both the inner core and outer shell; however, due to the specific alignment of the energy bands, charges relevant to the photodetection process migrate towards the outer shell.

The performance of the device is comparable with the reported silicon- or germanium-based photodetectors. Efforts are underway to explore nanowire transistor for single-photon detection and high-speed applications in nanophononics.