TY - GEN
T1 - Surface characterization of Ga-doped ZnO layers
AU - McNamara, Joy Dorene
AU - Ferguson, J. D.
AU - Foussekis, M.
AU - Ruchala, I.
AU - Reshchikov, M. A.
AU - Baski, A. A.
AU - Liu, H.
AU - Avrutin, V.
AU - Morkoç, H.
N1 - Funding Information:
This work was supported by the National Science Foundation (DMR 0804679).
PY - 2012
Y1 - 2012
N2 - Epitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400°C under metal-and 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.
AB - Epitaxial ZnO layers heavily doped with Ga (GZO) were grown at 400°C under metal-and 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.
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U2 - 10.1557/opl.2011.722
DO - 10.1557/opl.2011.722
M3 - Conference contribution
AN - SCOPUS:84455171995
SN - 9781605112923
T3 - Materials Research Society Symposium Proceedings
SP - 77
EP - 82
BT - Transparent Conducting Oxides and Applications
T2 - 2010 MRS Fall Meeting
Y2 - 29 November 2010 through 3 December 2010
ER -