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New Visible Light Absorbing Materials for Solar Fuels, Ga(Sbx)N1-X

Monday, May 12, 2014: 09:00
Nassau, Ground Level (Hilton Orlando Bonnet Creek)
S. Sunkara, V. K. Vendra (University of Louisville), J. B. Jasinski (University of Louisville, Conn Center for Renewable Energy Research), T. G. Deutsch (NREL), M. Menon (University of Kentucky), K. Rajan (University of Louisville), and M. K. Sunkara (University of Louisville, Conn Center for Renewable Energy Research)
In this work large band gap bowing of dilute antimonide alloys of gallium nitride, Ga(Sbx)N1-x has been investigated. Our computational calculations using first principles density functional theory2 revealed that a small amount of Sb incorporation is sufficient to achieve a significant band gap reduction in GaN from 3.4eV to 2eV. Theoretical calculations predicted that Ga(Sb)xN1-x alloys with 2 eV band gap straddle the electrochemical potentials of the hydrogen and oxygen evolution reactions. Theoretical computations with Sb composition beyond 7% change the electronic band gap from direct to indirect.

Synthesis of crystalline GaSbxN1-x alloys were carried out using metal organic chemical vapor deposition using trimethyl gallium (TMGa) and Trimethyl Antimony (TMSb) and ammonia at x values ranging from 0-8%. Synthesis was carried out on different planar substrates and GaN nanowires. X-ray diffraction measurements showed a monotonic increase in the lattice with increase in antimonide composition which corroborates with theoretical calculations.  Optical measurements like UV-Vis spectroscopy and photocurrent spectroscopy suggested a rapid decrease in band gap from 3.4 to 2 eV with small concentration of antimonide incorporation. Experimental data from optical measurements indicated direct band gap transition for alloys less than 7at% and an indirect band gap transition for alloys beyond 7% as shown in fig. 1. In addition Mott Schottky measurements showed that Ga(Sb)xN1-x alloys ranging from 0-8% straddle the water oxidation and reduction potentials in agreement to computational calculations. Moreover, the photo-electrochemical data on activity and stability suggest that these alloys are highly suitable for solar water splitting under visible light irradiation.

Fig. 1 Tauc plots for direct transition and indirect transition for 2 % Sb (a,b) and 8 % Sb (c,d).

Acknowledgements: Financial support from US Department of Energy (DE-FG02-07ER46375) and NSF (DMS1125909).

References:

1. S. Sunkara, V. Vendra, J. Jasinski, T. Deutsch, A.N. Andriotis, K. Rajan, M. Menon and M.K. Sunkara, “New Visible Light Absorbing Materials for Solar Fuels, Ga(Sbx)N1-x ”, In Review (2013)

2. R.M. Sheetz, E. Richter, A.N. Andriotis, C. Pendyala, M.K. Sunkara and M. Menon, “Visible light absorption and large band gap bowing in dilute alloys of gallium nitride with antimony”, Phys. Rev. B, 84, 075304 (2011)

See more of: Solar Hydogen Generation
See more of: F5: Solar Fuels and Photocatalysts 3
See more of: Fuel Cells, Electrolyzers, and Energy Conversion
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