The effects of shell layer morphology and processing on the electrical and photovoltaic properties of silicon nanowire radial p super(+)-n super(+) junctions

Single wire p super(+)-n super(+) radial junction nanowire solar cell devices were fabricated by low pressure chemical vapor deposition of n super(+) silicon shell layers on p super(+) silicon nanowires synthesized by vapor-liquid-solid growth. The n super(+)-shell layers were deposited at two growt...

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Bibliographic Details
Published in:Nanoscale 2015-04, Vol.7 (16), p.7267-7274
Main Authors: Wang, Xin, Ke, Yue, Kendrick, Chito E, Weng, Xiaojun, Shen, Haoting, Kuo, Mengwei, Mayer, Theresa S, Redwing, Joan M
Format: Article
Language:English
Subjects:
Annealing
Coating
Density
Deposition
Devices
Diodes
Nanowires
Silicon
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Summary:Single wire p super(+)-n super(+) radial junction nanowire solar cell devices were fabricated by low pressure chemical vapor deposition of n super(+) silicon shell layers on p super(+) silicon nanowires synthesized by vapor-liquid-solid growth. The n super(+)-shell layers were deposited at two growth temperatures (650 degree C and 950 degree C) to study the impact of shell crystallinity on the device properties. The n-type Si shell layers deposited at 650 degree C were polycrystalline and resulted in diodes that were not rectifying. A pre-coating anneal at 950 degree C in H sub(2) improved the structural quality of the shell layers and yielded diodes with a dark saturation current density of 3 10 super(-5) A cm super(-2). Deposition of the n-type Si shell layer at 950 degree C resulted in epitaxial growth on the nanowire core, which lowered the dark saturation current density to 3 10 super(-7) A cm super(-2) and increased the solar energy conversion efficiency. Temperature-dependent current-voltage measurements demonstrated that the 950 degree C coated devices were abrupt junction p super(+)-n super(+) diodes with band-to-band tunneling at high reverse-bias voltage, while multi-step tunneling degraded the performance of devices fabricated with a 950 degree C anneal and 650 degree C coating. The higher trap density of the 950 degree C annealed 650 degree 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 super(+)-n super(+) junction interface.
ISSN:2040-3364
2040-3372
DOI:10.1039/c5nr00512d