News

Home > News > SJTU Research Team’s Findings Changing the Classical Photoconductive Gain Theory

SJTU Research Team’s Findings Changing the Classical Photoconductive Gain Theory

March 06, 2020      Author: University of Michigan - Shanghai Jiao Tong University Joint Institute

Recently, Professor Dan Yaping’s Research Team from University of Michigan - Shanghai Jiao Tong University Joint Institute published their latest research paper titled “Explicit Gain Equations for Single Crystalline Photoconductors” in the international top academic journal ACS Nano (IF: 13.903). The corresponding author is Professor Dan Yaping, and the co-first authors are doctural student He Jiajing and doctoral graduate Chen Kaixiang. Doctoral student Wang Xiaoming, Professor He Yongning from Xi’an Jiao Tong University and his student Huang Chulin also participated in the research.

 

Research Paper Link: https://pubs.acs.org/doi/pdf/10.1021/acsnano.9b09406

 

Abstract

 

 

Photoconductors based on semiconducting thin films, nanowires, and two-dimensional atomic layers have been extensively investigated in the past decades. However, there is no explicit photogain equation that allows for fitting and designing photoresponses of these devices. In this work, we managed to derive explicit photogain equations for silicon nanowire photoconductors based on experimental observations. The silicon nanowires were fabricated by patterning the device layer of silicon-on-insulator wafers by standard lithography that were doped with boron at a concentration of 8.6 × 1017 cm3. It was found that the as-fabricated silicon nanowires have a surface depletion region 32 nm wide. This depletion region protects charge carriers in the channel from surface scatterings, resulting in the independence of charge carrier mobilities on nanowire size. Under light illumination, the depletion region logarithmically narrows down, and the nanowire channel widens accordingly. Photo Hall effect measurements show that the nanowire photoconductance is not contributed by the increase of carrier concentrations but by the widening of the nanowire channel. As a result, a nanowire photoconductor can be modeled as a resistor in connection with floating Schottky junctions near the nanowire surfaces. Based on the photoresponses of a Schottky junction, we derived explicit photogain equations for nanowire photoconductors that are a function of light intensity and device physical parameters. The gain equations fit well with the experimental data, from which we extracted the minority carrier lifetimes as tens of nanoseconds, consistent with the minority carrier lifetime in nanowires reported in literature.