Effective Separation of Photogenerated Electron–Hole Pairs by Radial Field Facilitates Ultrahigh Photoresponse in Single Semiconductor Nanowire Photodetectors

• Published in: Journal of physical chemistry. C Vol. 124; no. 41; pp. 22808 - 22816
• Main Authors: Sett, Shaili, Raychaudhuri, A. K
• Format: Journal Article
• Language: English
• Published: American Chemical Society 15.10.2020
• Subjects: C: Physical Processes in Nanomaterials and Nanostructures
• ISSN: 1932-7447; 1932-7455
• DOI: 10.1021/acs.jpcc.0c06582

We report an investigation on the observation of ultrahigh photoresponse (photogain, G Pc > 106) in single nanowire photodetectors of diameter <100 nm. The investigation, which is a combination of experimental observations and theoretical analysis of the ultrahigh optical response of semiconductor nanowires, has been carried out with an emphasis on Ge nanowires. Semiconductor nanowire photodetectors show a signature of photogating where G Pc rolls off with increasing illumination intensity. We show that surface band bending due to depleted surface layers in nanowires induces a strong radial field (∼108 V/m at the nanowire surface) that causes physical separation of photogenerated electron–hole pairs. This was established quantitatively through a self-consistent theoretical model based on coupled Schrodinger and Poisson equations. It shows that carrier separation slows down the surface recombination velocity to a low value (<1 cm/s), thus reducing the carrier recombination rate and extending the recombination lifetime by a few orders of magnitude. An important outcome of the model is the prediction of G Pc ∼ 106 in a single Ge nanowire (with diameter 60 nm), which matches well with our experimental observation. The model also shows an inverse dependence of G Pc on the diameter that has been observed experimentally. Though carried out in the context of Ge nanowires, the physical model developed has general applicability in other semiconductor nanowires as well.