Semiconductor nanowires are inspiring new devices that make use of their low dimensionality (1D) and large surface area (at a given volume), such as flexible electronics or optical interconnections on a chip. They are also promising as photodetectors. Their dielectric properties (which are very different from their environment) and their diameter (often smaller than the wavelength of the detected light) allow the engineering of their refractive index or electrical capacity, associated with the absorption characteristics of solid material.

There are two ways to activate a photocurrent in a GaN nanowire. The first way is by absorbing photons of energy higher than the gap of GaN (ultraviolet), which leads to electronic transitions known as interbands. The second way is by absorbing "resonant" infrared energy photons, tuned to the permitted electronic transitions inside the GaN conduction band. The geometry of the heterostructure thus allows fine-tuning the wavelength to be detected.

GaN/AlN heterostructures are well suited for these two processes, respectively in the UV-B and in the 1.55 µm near-infrared window of telecommunications. GaN has the extra advantage of being robust and resistant to extreme environments.

Physicists at the Inac have manufactured photodetectors consisting of a GaN nanowire containing GaN/AlN heterostructures. These nanowires were isolated and observed by transmission electron microscopy. In determining the dimensions of the heterostructure and the doping profile in the nanowires, the researchers were able to optimize the effectiveness of the devices.

They finally obtained a UV-B detector nearly one hundred times more sensitive than the current state of the art, as well as the first 1.55 µm photodetector to be included in a nanowire.

This work was conducted in collaboration with researchers from the CNRS, the Institut Néel (Université Grenoble Alpes) and the Justus Liebig University in Giessen (Germany). In addition, the work benefited from the use of the CEA-Minatec nanocharacterization facility.