Mahendra Sunkara1,Sonia Calero1,Madhu Menon1
University of Louisville1
Mahendra Sunkara1,Sonia Calero1,Madhu Menon1
University of Louisville1
Dilute anion alloys of III-nitrides are interesting as their band gap and band edges can be engineered suitably for photoelectrochemical water splitting [1]. In addition, they are direct band gap semiconductors with high absorption coefficients, good mobility, and charge-transport characteristics, i.e., lower Auger recombination [2]. For instance, it has been conclusively shown through theory and experiment that the band gap of GaN can be reduced from 3.45 eV, down to 1.7 eV upon 2-8 % of antimony incorporation (nitrogen substitution) [1]. The described anion alloying promotes valence band [3] as opposed to conduction band offsets, the latter being undesirable as they would typically compromise the straddling of the hydrogen reduction potential.<br/>Significant challenges exist in the production of devices based on III-V semiconductors due to limited or non-availability of suitable techniques for growing best quality films with III-Nitrides alloyed with anions. Towards that objective, a new synthesis technique has been developed for the growth of GaSb<sub>x</sub>N<sub>1-x</sub> and GaBi<sub>y</sub>N<sub>1-y </sub>0-D and 1-D structures, the Plasma-Assisted Vapor Liquid Phase Epitaxy (PA-VLPE) method [4] enables the control of anion charged species concentration, i. e., N+, Sb+, Bi+, that diffuse through a molten gallium layer and crystallize at the gallium/substrate interface. Single crystal films with antimony and bismuth incorporation of up to 0.9% and 1.1%, respectively, have been obtained without conducing to delocalized broadening of the valence band Density of States of these alloys. Similarly, copper catalyzed nanowire growth with anion incorporation levels comparable to the ones obtained through MOCVD have successfully produced visible light absorbing Ga (Sb or Bi)N alloys, via PA-VLPE.<br/>GaSb<sub>y</sub>P<sub>1-y</sub> alloys have been deposited on silicon substrates through Halide Vapor Phase Epitaxy with growth rates of up to 500 um/h and antimony incorporation between 3.7 and 6.7%. From experimental results, the effect of antimony on the optoelectronic properties of these alloys suggests the band gap reduction versus pure gallium phosphide does not occur for the indirect transition at 2.26 eV but rather for the direct one at 2.68 eV. Alloys with 2.2-2.5 eV direct bandgaps outperform single crystal 2.26 eV indirect gallium phosphide in onset potential and fill factor when tested in 1 M H<sub>2</sub>SO<sub>4</sub>and posses lower charge transfer resistance at the alloy/electrolyte interface even without the use of catalysts [5].<br/><b>Acknowledgements:</b> Some of the work was supported earlier with financial support from US Department of Energy (DE-FG02-07ER46375) and NSF (DMS1125909).<br/><b>References</b><br/>[1] S. Sunkara<i> et al.</i>, "New Visible Light Absorbing Materials for Solar Fuels, Ga(Sb-x)N1-x," <i>Advanced Materials, </i>vol. 26, no. 18, pp. 2878-2882, May 2014, doi: 10.1002/adma.201305083.<br/>[2] C.-K. Tan, "Dilute Anion III-Nitride semiconductor materials and nanostructures," Doctor of Philosophy in Electrical Engineering, Electrical Engineering, Lehigh University, 2016.<br/>[3] N. A. Andriotis, R. M. Sheetz, R. Ernst, and M. Madhu, "Band alignment and optical absorption in Ga(Sb)N alloys," <i>Journal of Physics: Condensed Matter, </i>vol. 26, no. 5, p. 055013, 2014.<br/>[4] D. Jaramillo, J. Jasinski and M. Sunkara, <i>“</i>Liquid Phase Epitaxial Growth of Gallium Nitride”<i>, Crystal Growth and Design,</i> 19, 11, 6577-6585(2019).<br/>[5] S. J. Calero-Barney, W. Paxton, P. Ortiz, and M. K. Sunkara, "Gallium antimonide phosphide growth using Halide Vapor Phase Epitaxy," (in English), <i>Solar Energy Materials and Solar Cells, </i>Article vol. 209, p. 9, Jun 2020, Art no. 110440, doi: 10.1016/j.solmat.2020.110440.