Structural studies of GaN 1-x As x and GaN 1-x Bi x alloys for solar cell applications

Z. Liliental-Weber*, Roberto dos Reis, A. X. Levander, K. M. Yu, W. Walukiewicz, S. V. Novikov, C. T. Foxon

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations

Abstract

We have discovered materials with a wide tunability of the band gap that opens the possibility to achieve a desirable material for multi-junction solar cells. Two different alloy systems have been studied. GaN 1-xAs x alloys over the entire composition range were grown by plasma-assisted MBE at low temperature on crystalline and amorphous (glass) substrates. For growth on sapphire the alloys are amorphous in the composition range of 0.17<x<0.75, but for growth on glass the composition range for amorphous alloys extends to x∼0.1. The bandgap of the GaN 1-xAs x alloys ranges from 3.4-0.7 eV, covering a large part of the solar spectrum, therefore this material is potentially useful for solar energy conversion. The substitution of N by Bi in GaN forming GaN 1-x Bi x is extremely difficult since Bi and N have even larger differences in size and electronegativity. TEM studies of GaN 1-xBi x with x up to 0.2 show that the alloy is not entirely amorphous. Small crystallites embedded in an amorphous matrix are observed and Bi segregation was confirmed by Electron Energy Loss studies. A strong reduction in band gap is observed in samples with increasing Bi, suggesting the formation of a random alloy but low energy absorption tail may be related to the presence of the crystallites observed by TEM.

Original languageEnglish (US)
Pages (from-to)1586-1589
Number of pages4
JournalPhysica Status Solidi (C) Current Topics in Solid State Physics
Volume9
Issue number7
DOIs
StatePublished - Jul 1 2012

Keywords

  • Bandgap
  • Crystalline to amorphous transition
  • TEM studies

ASJC Scopus subject areas

  • Condensed Matter Physics

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