Optical and electrical investigation of semiconducting amorphous Si:P alloy thin films

• Published in: Journal of applied physics 1995-01, Vol.77 (1), p.301-307
• Main Authors: Li, X.-H., Carlsson, J. R. A., Gong, S. F., Hentzell, H. T. G., Liedberg, B.
• Format: Article
• Language: English
• ISSN: 0021-8979; 1089-7550
• DOI: 10.1063/1.359392

Measurements are reported on the infrared (IR) absorption, the optical band gap, and the dark conductivity of amorphous silicon-phosphorus alloy thin films (a-Si:P) with 20–44 at. % P prepared by coevaporation of Si and P. The results show that the optical band gap can be tailored in a range of 1.5–2.15 eV by varying the P concentration and the annealing temperature. The band gap for the sample with 20 at % P is the widest (1.70–1.82 eV) when annealed at temperatures ≤600 °C. From the IR-absorption study, a stretching mode associated with Si—P bonds at 465–474 cm−1 has been found for all alloy films. An evolution (shift or sharpening) of the Si—P absorption band with annealing temperature and P concentration have also been observed. Based on the IR-absorption study the change of bonding structures in the alloy films is discussed. Conductivity measurements show that two electron conduction processes mainly exist in the investigated temperature range: extended-state conduction in the conduction band at high temperatures and hopping conduction in the band tail at low temperatures. The transition temperature is around room temperature (14–55 °C), indicating that the carriers may mainly drift by hopping even at room temperature. The correlation between the optical band gap and the bonding structure is discussed.