title: The effects of shell layer morphology and processing on the electrical and photovoltaic properties of silicon nanowire radial p+ - n+ junctions.
abstract: Single wire p(+)-n(+) radial junction nanowire solar cell devices were fabricated by low pressure chemical vapor deposition of n(+) silicon shell layers on p(+) silicon nanowires synthesized by vapor-liquid-solid growth. The n(+)-shell layers were deposited at two growth temperatures (650 °C and 950 °C) to study the impact of shell crystallinity on the device properties. The n-type Si shell layers deposited at 650 °C were polycrystalline and resulted in diodes that were not rectifying. A pre-coating anneal at 950 °C in H2 improved the structural quality of the shell layers and yielded diodes with a dark saturation current density of 3 × 10(-5) A cm(-2). Deposition of the n-type Si shell layer at 950 °C resulted in epitaxial growth on the nanowire core, which lowered the dark saturation current density to 3 × 10(-7) A cm(-2) and increased the solar energy conversion efficiency. Temperature-dependent current-voltage measurements demonstrated that the 950 °C coated devices were abrupt junction p(+)-n(+) diodes with band-to-band tunneling at high reverse-bias voltage, while multi-step tunneling degraded the performance of devices fabricated with a 950 °C anneal and 650 °C coating. The higher trap density of the 950 °C annealed 650 °C coated devices is believed to arise from the polycrystalline nature of the shell layer coating, which results in an increased density of dangling bonds at the p(+)-n(+) junction interface.
authors: Department of Electrical Engineering, Material Research Institute, The Pennsylvania State University, University Park, PA16802, USA.
authors: Xin
authors: X
authors: Wang
authors: Yue
authors: Y
authors: Ke
authors: Chito E
authors: CE
authors: Kendrick
authors: Xiaojun
authors: X
authors: Weng
authors: Haoting
authors: H
authors: Shen
authors: Mengwei
authors: M
authors: Kuo
authors: Theresa S
authors: TS
authors: Mayer
authors: Joan M
authors: JM
authors: Redwing