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

Research output: Contribution to journalArticlepeer-review

10 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 languageAmerican English
Article numberArticle No. 110468
Number of pages6
JournalSolar Energy Materials and Solar Cells
Volume209
DOIs
StatePublished - 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)

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