| AVS 57th International Symposium & Exhibition | |
| Energy Frontiers Topical Conference | Tuesday Sessions |
| Session EN+TF-TuA |
| Session: | Thin Films for Photovoltaics |
| Presenter: | T.L. Williamson, Los Alamos National Laboratory |
| Authors: | T.L. Williamson, Los Alamos National Laboratory M.A. Hoffbauer, Los Alamos National Laboratory K.M. Yu, Lawrence Berkeley National Laboratory L.A. Reichertz, Lawrence Berkeley National Laboratory W. Walukiewicz, Lawrence Berkeley National Laboratory |
| Correspondent: | Click to Email |
The wide band gap tunability of InxGa1-xN thin films (0.7 eV to 3.4 eV, 1>x>0) makes them ideal for efficient photovoltaic (PV) devices. However, growing high-quality In-rich InxGa1-xN films with strong photoluminescence in the green-to-red portions of the visible spectrum has faced considerable challenges due to indium phase segregation and other materials issues. These challenges have precluded the growth of both In-rich InGaN and compositionally graded InGaN materials, and make it difficult to grow higher bandgap Ga-rich materials on top of lower bandgap In-rich materials. Overcoming these difficulties using conventional epitaxial techniques is challenging due to the low decomposition temperatures of In-rich materials (e.g. InN~550°C) and the relatively high growth temperatures for Ga-rich materials (e.g. GaN >800°C).
Energetic neutral atom beam lithography & epitaxy (ENABLE) is a low-temperature thin film growth technology recently developed at LANL that utilizes a collimated beam of energetic neutral N atoms (kinetic energies 0.5 to 5.0 eV) to react with evaporated Ga and In metals to grow InGaN. ENABLE is similar to MBE, but provides a much larger N atom flux and correspondingly high film growth rate. The high kinetic energy of the reactive N atoms substantially reduces the need for high substrate temperatures, making isothermal growth over the entire InGaN alloy composition range possible at rates of >3 microns/hr with no toxic precursors or waste products.
Data on film photoluminescence, crystallinity, electrical properties, doping, and electro-luminescence of InxGa1-xN, graded InxGa1-xN, and GaN films grown using ENABLE over the full composition range will be presented. ENABLE-grown InxGa1-xN films show strong photo- and electro-luminescence spanning the entire visible region of the spectrum, with reasonable carrier mobilities background carrier concentrations typically in the low 1017 range. Evidence for p-type doping of In-rich InGaN films and characterization of p/n junctions will be discussed along with the prospects for using ENABLE to fabricate efficient PV devices.