Abstract
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).
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