We report an atomistic model established for electronic structure calculations of GaBiAs (0 < Bi < 12%) alloys based on empirical tight binding parameters. Alloy supercells consisting of 1000 and 8000 atoms are relaxed using valence force field (VFF) method, including anharmonic corrections to the Keating potential. Nearest neighbor tight binding Hamiltonian is solved for electronic spectra by representing each atomic sight with sp3s* parameters including spin orbit coupling (10-band model). The sp3s* tight binding parameters are designed to reproduce previously reported bulk band structures for GaAs and GaBi. A good agreement of our band structure for GaBi with the previous LDA+C calculations is demonstrated. Our calculations indicate a reduction of ~63-80 meV/ %Bi in band gap of the GaBiAs. Recent experimental data indicates a crossing between energy gap (Eg) and spin-orbital coupling (Δo) for Bi ~ 10.5% which closely match with our calculations. Finally, we analyze the character of Bi resonant state inside 1000 atoms GaBiAs supercell containing a single Bi atom. The computed energy and charge density distribution of Bi resonant state indicates that the Bi resonant state lies ~250 meV below the valence band edge and is ~60% localized on Bi site and its four nearest Ga neighbors. A close agreement of our calculations with the experimental data for periodic GaBiAs supercells allows us to extend our study for strained GaBiAs grown on top of GaAs substrates. All simulations are performed using NEMO 3-D simulator.
Dr. Muhammad Usman was graduated from the Electrical & Computer Engineering Department of Purdue University in August 2010. He is currently working as a researcher at Tyndall National Institute. His area of research is theory, modeling, simulations, and computation of semiconductor materials, alloys, hetero-structures, and optoelectronic devices. Dr. Usman has several collaborations with the renowned experimental groups at Imperial College London UK, Kobe University Japan, National Nanotechnology Lab Italy, Surrey University UK, etc.
Dr. Usman's most recent work involves the electronic structure theory of the novel bismide alloys (GaBiAs, GaBiNAs, InGaBiAs) which are expected to revolutionize the design of the next generation semiconductor lasers working at the telecomm wavelengths. This work which is being done in collaboration with the experimental and industry partners involves establishing the first-ever tight binding models for the bismide materials and the subsequent derivation of the 12/14-band k.p models to study the loss/gain mechanisms in the bismide quantum well nano-structures. Further details about this project can be found at: http://www.biancho.org/
Dr. Usman is also affiliated with NCN and nanoHub.org. He is a junior member of American Physical Society (APS), and a member of IEEE and Material Research Society (MRS).
Muhammad Usman, Christopher A. Broderick, Andrew Lindsay, and Eoin P. O'Reilly
Tyndall National Institute, Lee Maltings, Dyke Parade, Cork Ireland
European Framework FP7 funds, BIANCHO (www.biancho.org), Tyndall National Institute Lee Maltings Cork Ireland, and Department of Physics University College Cork Ireland
1. M. Usman, C.A. Broderick, A. Lindsay, and E. P. O'Reilly, Physical Review B 84, 245202 (2011)
2. C.A. Broderick, M. Usman, and S. Sweeney, E. P. O'Reilly, (INVITED REVIEW PAPER) IOP Semicond. Sci. Technol. 27, 094011 (2012)
3. "The potential role of Bismide alloys in future photonic devices", S.J. Sweeney, Z. Batool, K. Hild, S.R. Jin, and T.J.C. Hosea, IEEE Proceedings of 13th International Conference on Transparent Optical Networks (ICTON), 2011, DOI:10.1109/ICTON.2011.5970829
4. "Tight binding analysis of the electronic structure of dilute bismide and nitride alloys of GaAs", C. A. Broderick, M. Usman, A. Lindsay and E. P. O'Reilly, IEEE Proceedings of 13th International Conference on Transparent Optical Networks (ICTON), 2011, DOI: 10.1109/ICTON.2011.5970828
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