| AVS 63rd International Symposium & Exhibition | |
| Electronic Materials and Photonics | Friday Sessions |
| Session EM-FrM |
| Session: | Late Breaking News on Electronic Materials and Devices |
| Presenter: | Steven Durbin, Western Michigan University |
| Authors: | R. Makin, Western Michigan University N. Senabulya, University of Michigan J.P. Mathis, University of Michigan R. Clarke, University of Michigan T. Veal, University of Liverpool S.M. Durbin, Western Michigan University |
| Correspondent: | Click to Email |
Chalcopyrite heterovalent ternary compounds can undergo an order-disorder transition between an ordered chalcopyrite structure and a disordered zinc-blende-like phase. Unlike in adamantine alloys, the disorder results in a band gap reduction in the disordered phase relative to the band gap of the ordered lattice. ZnSnN2 represents an interesting member of the chalcopyrite family of materials, due to its earth abundant element constituents and a band gap of use for solar cells. It is also part of the Zn-IV-N2 family of materials, whose band gaps span from the infrared to the UV. Density functional theory (DFT) calculations predict the ordered ZnSnN2 phase to have an orthorhombic lattice and a direct band gap of 2.0 eV. Using special quasirandom structures (SQS) to model the disordered Zn and Sn cation sub-lattice, DFT simulations predict that the band gap for the disordered ZnSnN2 phase will be close to 1.0 eV and will have a hexagonal lattice. This almost 1.0 eV reduction of the band gap of ZnSnN2 presents an opportunity for band gap engineering by controlling the disorder on the cation sublattice. Recently, however, an alternative theory of disorder for ZnSnN2 has been proposed that does not depend on cation lattice disorder. This alternate disorder, unlike the cation disorder model, does not violate the octet rule locally and results in a band gap that is independent of the order. If either model is accurate is presently unknown.
A series of films ha s been grown by plasma assisted molecular beam epitaxy in order to investigate the possibility of controlled cation disorder as well as its effects on physical and electr onic properties of the material. By varying the growth conditions, specifically either the metal flux to the nitrogen pressure or the substrate , w e have confirmed the existence of both the hexagonal and orthorhombic phase s of the crystal via synchrotron x-ray diffraction ( performed at Argonne National Lab o ratory . All of the films at present have a high free carrier concentration (in excess of 10 19 cm -3 ). Taking into account the Burstein-Moss shift caused by the high carrier concentration and calculating the effective masses of the carriers from parabolic fits to the density results, the optically measured band gap s appear to be consistent with the DFT calculations; the band gap show s a clear dependence on cation disorder.