Electronic Properties of Hydrogenated Amorphous Silicon--Germanium Alloys and Long-Range Potential Fluctuations

S. R. Sheng, G. S. Sun, J. Liebe, A. Kattwinkel, R. Braunstein, B. P. Nelson, B. Von Roedern, K. Bärner

Research output: Contribution to journalArticlepeer-review

8 Scopus Citations


The charge transport properties and microstructure of hydrogenated amorphous silicon-germanium alloys (a-SiGe:H) prepared by the hot-wire chemical vapor deposition (HWCVD) process as a function of alloy composition have been investigated in detail by employing the photoconductive frequency mixing and small angle X-ray scattering techniques. Evidence for the presence of long-range potential fluctuations in a-SiGe:H alloys is revealed from the measurements of electric field dependence of the drift mobility. The effect of the long-range potential fluctuations is enhanced by the addition of Ge to the alloy system that results in the deterioration of the opto-electronic properties of a-SiGe:H alloys. Through the drift mobility field dependence, the depth and range of the potential fluctuations as a function of alloy composition are determined, and subsequently the charged defect density. It was found that at a composition of ∼ 10% Ge in Si, the photoresponse begins to decrease monotonically with increasing Ge content due to the decreases in the drift mobility and lifetime as a result of an increase in the concentration of charged defects, which lead to the long-range potential fluctuations whose depth increases, while the range decreases. The sharp changes in these parameters are demonstrated to be attributed to a concurrent abruptly increased structural heterogeneity due to the introduction of microvoids.

Original languageAmerican English
Pages (from-to)490-496
Number of pages7
JournalMaterials Science and Engineering: A
Issue number1-2
StatePublished - 2002

NREL Publication Number

  • NREL/JA-520-32592


  • Amorphous semiconductors
  • Electronic transport
  • Long-range potential fluctuations


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