Imaging Hole-Density Inhomogeneity in Arsenic-Doped CdTe Thin Films by Scanning Capacitance Microscopy

Chun Sheng Jiang; John Moseley; Chuanxiao Xiao; Steven Harvey; Eric Colegrove; Wyatt Metzger; Mowafak Al-Jassim; Stuart Farrell

doi:10.1016/j.solmat.2020.110468

Imaging Hole-Density Inhomogeneity in Arsenic-Doped CdTe Thin Films by Scanning Capacitance Microscopy

Chun Sheng Jiang, John Moseley, Chuanxiao Xiao, Steven Harvey, Eric Colegrove, Wyatt Metzger, Mowafak Al-Jassim, Stuart Farrell

Materials Science

National Renewable Energy Laboratory

Research output: Contribution to journal › Article › peer-review

12 Scopus Citations

Abstract

We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 10¹⁵–10¹⁸/cm³ within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several μm and hole density varying by one order of magnitude (low 10¹⁶ to low 10¹⁷/cm³). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.

Original language	American English
Article number	Article No. 110468
Number of pages	6
Journal	Solar Energy Materials and Solar Cells
Volume	209
DOIs	https://doi.org/10.1016/j.solmat.2020.110468 https://doi.org/10.1016/j.solmat.2020.110468
State	Published - 1 Jun 2020

Bibliographical note

Publisher Copyright:
© 2020 Elsevier B.V.

NREL Publication Number

NREL/JA-5K00-76039

Keywords

As-doping
Carrier concentration
Cathodoluminescence (CL)
CdTe solar cell
Kelvin probe force microscopy (KPFM)
Scanning capacitance microscopy (SCM)

UN SDGs

This output contributes to the following UN Sustainable Development Goals (SDGs)

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Jiang, C. S., Moseley, J., Xiao, C., Harvey, S., Colegrove, E., Metzger, W., Al-Jassim, M., & Farrell, S. (2020). Imaging Hole-Density Inhomogeneity in Arsenic-Doped CdTe Thin Films by Scanning Capacitance Microscopy. Solar Energy Materials and Solar Cells, 209, Article Article No. 110468. https://doi.org/10.1016/j.solmat.2020.110468, https://doi.org/10.1016/j.solmat.2020.110468

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title = "Imaging Hole-Density Inhomogeneity in Arsenic-Doped CdTe Thin Films by Scanning Capacitance Microscopy",

abstract = "We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 1015–1018/cm3 within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several μm and hole density varying by one order of magnitude (low 1016 to low 1017/cm3). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.",

keywords = "As-doping, Carrier concentration, Cathodoluminescence (CL), CdTe solar cell, Kelvin probe force microscopy (KPFM), Scanning capacitance microscopy (SCM)",

author = "Jiang, {Chun Sheng} and John Moseley and Chuanxiao Xiao and Steven Harvey and Eric Colegrove and Wyatt Metzger and Mowafak Al-Jassim and Stuart Farrell",

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AU - Jiang, Chun Sheng

AU - Moseley, John

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AU - Harvey, Steven

AU - Colegrove, Eric

AU - Metzger, Wyatt

AU - Al-Jassim, Mowafak

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N2 - We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 1015–1018/cm3 within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several μm and hole density varying by one order of magnitude (low 1016 to low 1017/cm3). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.

AB - We report nanometer-scale hole-density imaging in As-doped CdTe films by scanning capacitance microscopy (SCM). The hole-density profiling is validated by contrasting a CdTe cross-section sample made by molecular-beam epitaxy with systematically increased As doping in a staircase pattern over the range of 1015–1018/cm3 within a single film. In polycrystalline films, the carrier distribution is significantly nonuniform, with inhomogeneity ranging from several hundred nm to several μm and hole density varying by one order of magnitude (low 1016 to low 1017/cm3). This nonuniformity is distributed randomly, independent of the grain structure and grain boundaries (GBs). Kelvin probe force microscopy (KPFM) maps the surface potential and is correlated to cathodoluminescence (CL) and SCM by imaging over identical areas. Higher potential and lower CL intensity are found on GBs but not by SCM contrast; this indicates positive GB charging and recombination, but not GB-specific hole-density changes. The overall KPFM potential image is in rough agreement with the SCM carrier distribution and indicates band-edge potential fluctuations. Nonuniform carrier concentration, potential fluctuations, and defect recombination can all cause voltage and performance loss in As-doped CdTe solar technology.

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KW - Carrier concentration

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KW - CdTe solar cell

KW - Kelvin probe force microscopy (KPFM)

KW - Scanning capacitance microscopy (SCM)

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ER -

Imaging Hole-Density Inhomogeneity in Arsenic-Doped CdTe Thin Films by Scanning Capacitance Microscopy

Abstract

Bibliographical note

NREL Publication Number

Keywords

UN SDGs

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