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Surface Characterization of Ga-doped ZnO layers

Published online by Cambridge University Press:  05 April 2011

J.D. McNamara ,
J.D. Ferguson ,
M. Foussekis ,
I. Ruchala ,
M.A. Reshchikov ,
A.A. Baski ,
H. Liu ,
V. Avrutin  and
H. Morkoç
J.D. McNamara
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
J.D. Ferguson
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
M. Foussekis
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
I. Ruchala
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
M.A. Reshchikov
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
A.A. Baski
Affiliation:
Department of Physics, Virginia Commonwealth University, Richmond, VA 23284
H. Liu
Affiliation:
Department of Electrical and Computer Engineering, VCU, Richmond, VA 23284
V. Avrutin
Affiliation:
Department of Electrical and Computer Engineering, VCU, Richmond, VA 23284
H. Morkoç
Affiliation:
Department of Electrical and Computer Engineering, VCU, Richmond, VA 23284
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Abstract

Epitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400 °C under metaland oxygen-rich conditions in terms of metal-to-reactive oxygen ratio by plasma-assisted molecular beam epitaxy (MBE). Several atomic force microscopy (AFM) techniques were used to characterize the surface morphology and electrical properties of these GZO films in ambient conditions. Local I-V spectra indicate that layers grown under both O-rich and metal-rich conditions are highly resistive until a relatively high voltage sweep (±12 V) is used. After removal of an insulating surface layer, conduction is possible at lower voltages, but eventually the film resistivity increases and it again becomes insulating. In addition to local I-V spectra, local charge injection and subsequent surface potential measurements were used to probe surface charging characteristics. For charge injection experiments, a reverse-bias voltage is applied to the sample while scanning in contact mode with a metallized tip. The resultant change in surface potential due to trapped charge is subsequently observed using scanning Kelvin probe microscopy (SKPM). The layers deposited in a metal-rich environment demonstrate the expected behavior, but the O-rich layers show anomalous negative and positive charging. Finally, surface photovoltage (SPV) measurements using above-bandgap UV illumination were performed. The GZO layers produce SPV values of 0.4 to 0.5 eV, where the films deposited in an O-rich environment have slightly higher SPV values and faster restoration.

Keywords

transparent conductorscanning probe microscopy (SPM)morphology
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1315: Symposium MM – Transparent Conducting Oxides and Applications , 2011 , mrsf10-1315-mm06-25
Copyright
Copyright © Materials Research Society 2011

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References

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