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Anomalous behavior of the optical band gap of nanocrystalline zinc oxide thin films

Published online by Cambridge University Press:  31 January 2011

V. Srikant  and
D. R. Clarke
V. Srikant
Affiliation:
Materials Department, College of Engineering, University of California, Santa Barbara, California 93106
D. R. Clarke
Affiliation:
Materials Department, College of Engineering, University of California, Santa Barbara, California 93106
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Abstract

The optical band gap of ZnO films on fused silica in the carrier concentration regime of 1018−1020/cm3 is reported. Contrary to theoretical predictions there is an anomalous increase in the band gap of ZnO films at a carrier concentration of 5 × 1018/cm3, followed by an abrupt decrease at a critical concentration of 3−4 × 1019/cm3 before the optical band gap rises again. Similar observations have been made before, but an explanation of these observations was lacking. We propose a model based on the existence of potential barriers at the grain boundaries, causing quantum confinement of the electrons in the small grains realized in these films. Quantum confinement leads to the initial rise in the optical band gap. On increasing the carrier concentration to the critical value, the potentials at the grain boundaries collapse, leading to the abrupt decrease in the optical band gap. Above this carrier concentration the films behave according to existing many-body theories.

Type
Articles
Information
Journal of Materials Research , Volume 12 , Issue 6 , June 1997 , pp. 1425 - 1428
Copyright
Copyright © Materials Research Society 1997

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References

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