| AVS 61st International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Wednesday Sessions |
| Session EN+AS+EM+SE-WeM |
| Session: | Thin Film Photovoltaics |
| Presenter: | Nathaniel Feldberg, University at Buffalo-SUNY |
| Authors: | N. Feldberg, University at Buffalo-SUNY Y. Yang, University of Michigan W.M. Linhart, University of Liverpool, UK T.D. Veal, University of Liverpool, UK P.A. Stampe, Florida A&M University R.J. Kennedy, Florida A&M University D.O. Scanlon, University College London, UK L.F.J. Piper, Binghamton University N. Senabulya, University of Michigan R. Clarke, University of Michigan R.J. Reeves, University of Canterbury, New Zealand S. Durbin, Western Michigan University |
| Correspondent: | Click to Email |
In recent years Zn-IV-N2 compounds have seen increased interest as potential earth abundant element semiconductors for photovoltaic and solid state lighting applications. Several reports of successful growth for the Ge and Si containing compounds are extant as well as more recent publications on the Sn containing member of the family. This material offers a possible alternative to indium containing materials which have experienced large price fluctuations due to limited domestic supply, lack of recycling and heightened demand. Our films were grown by plasma assisted molecular beam epitaxy on (111)-yittria stabilized zirconia. In the case of an ordered lattice, density functional theory (DFT) predicts an orthorhombic structure; however, the disordered lattice is predicted to be pseudo-hexagonal. Reflection high energy electron diffraction patterns for these films indicate single crystal structure with hexagonal symmetry, consistent with X-ray diffraction measurements. Hall effect indicates carrier concentrations in the 3-10x1021 cm-3 range for which we would expect a significant Burstein-Moss shift. Contrary to expectations, optical measurements of absorption onset occur at higher energy in films with lower carrier concentrations. As in ZnSnP2, the bandgap is expected to narrow with the introduction of disorder for this material; this narrowing behavior is consistent with observed variations in absorption spectra. Of practical interest is the possibility of a material with a tunable bandgap without the need for traditional alloying. Zn-Sn-N2 is expected to have a bandgap varying from 1.1 to 2 eV controlled by the continuous degree of order in the cation sub-lattice. Although hard X-ray diffraction measurements of these films do not show any variation from a hexagonal structure, Hall measurements of carrier concentrations compared with absorption data indicates that our samples vary their absorption onset, not as would be expected from Burstein-Moss Shift, but in a manner consistent with a variation in the lattice order. DFT calculations indicate that there is a variation in the Density of States between the ordered and disordered films. Films which were consistent with increased order absorption are also consistent with an increased order density of states measured by HAXPES.
This project is supported by NSF grant DMR1244887 (Program Director Charles Ying), and EPSRC grant EP/G004447/2 .