The impact of processing conditions and post-deposition oxidation on the opto-electrical properties of hydrogenated amorphous and nano-crystalline Germanium films

Thierry de Vrijer, Ashwath Ravichandran, Bilal Bouazzata, Arno H.M. Smets

Research output: Contribution to journalArticleScientificpeer-review

1 Citation (Scopus)
9 Downloads (Pure)

Abstract

Low-cost multijunction photovoltaic devices are the next step in the solar energy revolution. Adding a bottom junction with a low bandgap energy material through plasma enhanced chemical vapor deposition (PECVD) processing could potentially provide a low-cost boost in conversion efficiency. A logical candidate for this low bandgap material is germanium. In this work we investigate the growth of PECVD processed hydrogenated amorphous/nano-crystalline germanium (a/nc-Ge:H), by characterizing over 100 samples, processed with a wide range of deposition pressures, powers, temperatures and GeH4 dilution in hydrogen, using elemental analysis, vibrational analysis and analysis of the opto-electrical properties. We have identified a small processing window in which nc-Ge:H films are processed reproducibly. We also report on the strong correlation between the refractive index of the films and the presence- and extent of post-deposition oxidation. Notably, the oxidation generally increased the photoresponse of the films, as it results in a decrease of room temperature σd by 1-3 orders of magnitude. However, oxidation results in an increase of the bandgap energy and therefore impedes the development of a low bandgap material. The lowest E04 we report is about 1.1eV, with an ETauc of 0.9eV and an σphd of 3.4.

Original languageEnglish
Article number120507
Pages (from-to)1-9
Number of pages9
JournalJournal of Non-Crystalline Solids
Volume553
DOIs
Publication statusPublished - 2021

Keywords

  • a-Ge:H
  • germanium
  • germanium oxide
  • nanocrystalline
  • oxidation
  • PECVD

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