Speaker
Dr
Atchara Punya
(Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, THAILAND 50200)
Description
The Zn(Ge,Sn)N$_2$ semiconductors are closely related to the (Al,Ga,In)N. Both families have band gaps that span the ultraviolet through the visible range. Attention in the II-IV-N$_2$ has grown recently, with success in synthesizing ZnSnN$_2$ reported in 2012 [1] and the recognition of some of their unique optoelectronic properties and the potential that provide for designing novel and useful optoelectronic devices [2, 3]. It is also of great interest that several members of the II-IV-N$_2$ family are made from earth-abandant and nontoxic elements.
We investigate lattice ordering phenomena for Zn(Ge,Sn)N$_2$ that are based on the wurtzite lattice, under the constraint that the octet rule be preserved. First-principles calculations of the energies of formation show that the differences in the energies of formation between Pna2$_1$ and Pmc2$_1$ crystal structures are 13±3 meV/fu (formula unit) for ZnSnN$_2$ and an order of magnitude larger for ZnGeN$_2$, and that for both materials the Pm31 structure, which contains only octet-rule-violating tetrahedra, has a significantly higher energy of formation and a signficantly lower band gap. The octet-rule-preserving model predicts a band gap that for ZnSnN$_2$ is relatively insensitive to cation-ordering. The violations of the octet rule lead to significant narrowing of the band gap. The observation that ZnGeN$_2$ orders in the Pna2$_1$ structure is consistent with the larger difference in the energies of formation of the Pna2$_1$ and Pmc2$_1$ structures in this case. The cation-ordering effects presented here has important implications for the optical, electronic and lattice properties of all wurtzite-based heterovalent ternaries.
1. N. Feldberg, B. Keen, J.D. Aldous, D.O. Scanlon, P.A. Stampe, R.J. Kennedy, R.J. Reeves, T.D. Veal, S.M. Durbin, Proc. 2012 IEEE Photovoltaics Specialists Conference, 002524 (2011).
2. Walter R.L. Lambrecht and Atchara Punya, III-nitride Semiconductors and their Modern Devices (Oxford University Press), chapt. 15 (2013).
3. Lu Han, Kathleen Kash and Hongping Zhao, Proc. of SPIE. 9003, 90030W-1 (2014).
Primary author
Dr
Atchara Punya
(Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, THAILAND 50200)
Co-author
Prof.
Walter R.L. Lambrecht
(Case Western Reserve University)
