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Title: Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering

Abstract

Radio frequency (rf) sputtered films of 10 at. % P{sub 2}O{sub 5}-doped zinc oxide (ZnO) were deposited at temperatures (T{sub d}) below the sublimation point of P{sub 2}O{sub 5} (T{sub d}<350 degree sign C) and at a range of oxygen pressures p(O{sub 2}). Ultraviolet-visible optical transmission measurements, x-ray photoelectron spectroscopy (XPS), and x-ray diffraction were used to examine the effects of p(O{sub 2}) during deposition on the band gap and on the bonding behavior of phosphorus. At both deposition temperatures studied (room temperature with unintentional heating and 125 degree sign C), an increase in phosphorus concentration with increasing p(O{sub 2}) was observed. However, the dependence of the band gap behavior on p(O{sub 2}) was observed to be dramatically different for the two deposition temperatures: room-temperature-deposited films show a redshift while films deposited at 125 degree sign C show a blueshift. Analysis of the oxygen 1s XPS peak shows a progressive formation of nonbridging (Zn-O-P) bond networks for room temperature films, whereas films grown at 125 degree sign C show increased (P-O-P) bond networks with increasing p(O{sub 2}). This indicates that a small degree of thermal activation considerably modifies the bonding behavior of phosphorus in ZnO. Implications of these results formore » the use of phosphorus as a p-type dopant for ZnO are discussed.« less

Authors:
; ; ; ;  [1];  [2]
  1. Department of Physics, University of Maryland, College Park, Maryland 20742 (United States)
  2. (United States)
Publication Date:
OSTI Identifier:
20982758
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 101; Journal Issue: 6; Other Information: DOI: 10.1063/1.2715551; (c) 2007 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHEMICAL BONDS; DOPED MATERIALS; ENERGY GAP; HEATING; OXYGEN; PHOSPHORUS; PHOSPHORUS OXIDES; RADIOWAVE RADIATION; RED SHIFT; SEMICONDUCTOR MATERIALS; SPUTTERING; SUBLIMATION; SURFACE COATING; TEMPERATURE RANGE 0273-0400 K; THIN FILMS; ULTRAVIOLET RADIATION; X-RAY DIFFRACTION; X-RAY PHOTOELECTRON SPECTROSCOPY; ZINC OXIDES

Citation Formats

Pugel, D. Elizabeth, Vispute, R. D., Hullavarad, S. S., Venkatesan, T., Varughese, B., and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742. Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering. United States: N. p., 2007. Web. doi:10.1063/1.2715551.
Pugel, D. Elizabeth, Vispute, R. D., Hullavarad, S. S., Venkatesan, T., Varughese, B., & Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742. Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering. United States. doi:10.1063/1.2715551.
Pugel, D. Elizabeth, Vispute, R. D., Hullavarad, S. S., Venkatesan, T., Varughese, B., and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742. Thu . "Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering". United States. doi:10.1063/1.2715551.
@article{osti_20982758,
title = {Oxygen-dependent phosphorus networking in ZnO thin films grown by low temperature rf sputtering},
author = {Pugel, D. Elizabeth and Vispute, R. D. and Hullavarad, S. S. and Venkatesan, T. and Varughese, B. and Department of Materials Science and Engineering, University of Maryland, College Park, Maryland 20742},
abstractNote = {Radio frequency (rf) sputtered films of 10 at. % P{sub 2}O{sub 5}-doped zinc oxide (ZnO) were deposited at temperatures (T{sub d}) below the sublimation point of P{sub 2}O{sub 5} (T{sub d}<350 degree sign C) and at a range of oxygen pressures p(O{sub 2}). Ultraviolet-visible optical transmission measurements, x-ray photoelectron spectroscopy (XPS), and x-ray diffraction were used to examine the effects of p(O{sub 2}) during deposition on the band gap and on the bonding behavior of phosphorus. At both deposition temperatures studied (room temperature with unintentional heating and 125 degree sign C), an increase in phosphorus concentration with increasing p(O{sub 2}) was observed. However, the dependence of the band gap behavior on p(O{sub 2}) was observed to be dramatically different for the two deposition temperatures: room-temperature-deposited films show a redshift while films deposited at 125 degree sign C show a blueshift. Analysis of the oxygen 1s XPS peak shows a progressive formation of nonbridging (Zn-O-P) bond networks for room temperature films, whereas films grown at 125 degree sign C show increased (P-O-P) bond networks with increasing p(O{sub 2}). This indicates that a small degree of thermal activation considerably modifies the bonding behavior of phosphorus in ZnO. Implications of these results for the use of phosphorus as a p-type dopant for ZnO are discussed.},
doi = {10.1063/1.2715551},
journal = {Journal of Applied Physics},
number = 6,
volume = 101,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • ZnO thin films were epitaxially grown on Al{sub 2}O{sub 3} (0001) substrates in a radio-frequency (rf) magnetron sputtering chamber. The surface morphology of ZnO was remarkably affected by the incorporation of a low-temperature grown ZnO buffer as well as the changes in rf-power. X-ray diffractions, combined with the surface micropits, revealed strain relaxations in the ZnO epilayers grown with higher rf-powers, which in turn caused a redshift to the intrinsic exciton absorption peak. Strain relaxations were also observed in the ZnO epilayers upon thermal annealing, which led to a redshift in the E{sub 2}{sup high} Raman mode. A factor ofmore » approx0.7 cm{sup -1} GPa{sup -1}, i.e., a biaxial stress of 1 GPa can shift the E{sub 2}{sup high} mode by 0.7 cm{sup -1}, was obtained. The point defects related absorptions and the exciton localizations were suppressed by annealing, which, in conjunction with the strain-relaxation induced redshift in the intrinsic-exciton absorptions, steepened the absorption edge and increased the optical bandgap energy of the ZnO epilayer.« less
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  • Phosphorus-doped p-type ZnO thin films were grown on sapphire by radio-frequency magnetron sputtering. The photoluminescence (PL) spectra revealed an acceptor bound exciton peak at 3.355 eV and a conduction band to the acceptor transition caused by a phosphorus related level at 3.310 eV. A study of the dependence of the excitation laser power density and temperature on the characteristics of the PL spectra suggests that the emission lines at 3.310 and 3.241 eV can be attributed to a conduction band to the phosphorus-related acceptor transition and a donor to the acceptor pair transition, respectively. The acceptor energy level of themore » phosphorus dopant was estimated to be located 127 meV above the valence band.« less
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