He Jiajing, Chen Kaixiang, Huang Chulin, Wang Xiaoming, He Yongning, Dan Yaping
State Key Laboratory of Advanced Optical Communication Systems and Networks, University of Michigan - Shanghai Jiao Tong University Joint Institute, Shanghai Jiao Tong University, Shanghai 200240, China.
School of Microelectronics, Xi'an Jiao Tong University, Xi'an, Shaanxi 710049, China.
ACS Nano. 2020 Mar 24;14(3):3405-3413. doi: 10.1021/acsnano.9b09406. Epub 2020 Mar 5.
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 × 10 cm. 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.
在过去几十年中，基于半导体薄膜、纳米线和二维原子层的光电导体受到了广泛研究。然而，目前尚无明确的光增益方程可用于拟合和设计这些器件的光响应。在这项工作中，我们基于实验观察成功推导了硅纳米线光电导体的明确光增益方程。通过标准光刻技术对浓度约为8.6×10 cm且掺硼的绝缘体上硅晶圆的器件层进行图案化来制备硅纳米线。发现所制备的硅纳米线具有约32 nm宽的表面耗尽区。该耗尽区保护沟道中的电荷载流子免受表面散射影响，使得电荷载流子迁移率与纳米线尺寸无关。在光照下，耗尽区对数式变窄，纳米线沟道相应变宽。光霍尔效应测量表明，纳米线光电导并非由载流子浓度增加所致，而是由纳米线沟道变宽引起。因此，纳米线光电导体可建模为与纳米线表面附近的浮动肖特基结相连的电阻器。基于肖特基结的光响应，我们推导了作为光强和器件物理参数函数的纳米线光电导体的明确光增益方程。增益方程与实验数据拟合良好，据此我们提取出少数载流子寿命为几十纳秒，这与文献报道的纳米线中的少数载流子寿命一致。
