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Growth by Molecular Beam Epitaxy of GaNAs Alloys with High As Content for Potential Photoanode Applications in Hydrogen Production

Published online by Cambridge University Press:  31 January 2011

Sergey V Novikov
Affiliation:
[email protected], University of Nottingham, School of Physics and Astronomy, Nottingham, United Kingdom
Chris R Staddon
Affiliation:
[email protected], University of Nottingham, School of Physics and Astronomy, Nottingham, United Kingdom
Andrey V Akimov
Affiliation:
[email protected], University of Nottingham, School of Physics and Astronomy, Nottingham, United Kingdom
Richard Campion
Affiliation:
[email protected], United States
Norzaini Zainal
Affiliation:
[email protected], University of Nottingham, School of Physics and Astronomy, Nottingham, United Kingdom
Anthony J Kent
Affiliation:
[email protected], University of Nottingham, School of Physics and Astronomy, Nottingham, United Kingdom
Tom Foxon
Affiliation:
[email protected], United States
Chien H Chen
Affiliation:
[email protected], Industrial Technology Research Institution, Photovoltaics Technology Center, Taiwan, Taiwan, Province of China
Kin M Yu
Affiliation:
[email protected], Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, California, United States
Wladek Walukiewicz
Affiliation:
[email protected], Lawrence Berkeley National Laboratory, Materials Sciences Division, Berkeley, California, United States
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Abstract

We have studied the low-temperature growth of GaNAs layers on sapphire substrates by plasma-assisted molecular beam epitaxy. We have succeeded in achieving GaN1-xAsx alloys over a large composition range by growing the films at temperature much below the normal GaN growth temperatures with increasing the As2 flux as well as Ga:N flux ratio. We found that the alloys with high As content x>0.1 are amorphous. Optical absorption measurements reveal a continuous gradual decrease of band gap from ˜3.4 eV to ˜1.4 eV with increasing As content. The energy gap reaches its minimum of ˜1.4 eV at the x˜0.6-0.7. For amorphous GaAsN alloys with x<0.3 the composition dependence of the band gap follows the prediction of the band anticrossing model developed for dilute alloys. This suggests that the amorphous GaN1-xAsx alloys have short-range ordering that resembles random crystalline GaN1-xAsx alloys. Such amorphous GaN1-xAsx alloys with tunable electronic structure may be useful as photoanodes in photo-electrochemical cells for hydrogen production.

Type
Research Article
Copyright
Copyright © Materials Research Society 2009

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