Aligned-Crystalline Si Films on Glass
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1066-A20-04
Aligned-Crystalline Si Films on Glass Alp T. Findikoglu1, Ozan Ugurlu2, and Terry G. Holesinger2 1 MPA-STC, Los Alamos National Laboratory, MS T004, Los Alamos, NM, 87544 2 MPA-STC, Los Alamos National Laboratory, MS K763, Los Alamos, NM, 87544 ABSTRACT We report structural and electronic properties of Aligned-Crystalline Si (ACSi) films on glass substrates. These films show enhanced majority carrier mobilities and minority carrier lifetimes with increasing crystallinity, i.e., with improving alignment and connectivity of the grains. A 0.4-µm-thick ACSi film with a total grain mosaic spread of 4.2° showed Hall mobility of 47 cm2/V.s for a p-type doping concentration of 1.9x1018 cm-3. A prototype n+/p/p+–type diode fabricated using a 4.2-µm-thick ACSi film showed minority carrier lifetime of ~3.5 µs and estimated diffusion length of ~30 µm in the p layer with a doping concentration of 5x1016 cm-3. INTRODUCTION This study describes microstructural and electronic properties of highly-crystalline Si, Aligned-Crystalline Si (ACSi), films that are epitaxially deposited on glass substrates. Glass substrates, due to their transparency, durability, and chemical robustness, are of particular interest for use in applications such as sensors, photovoltaics, and displays. However, since glass is amorphous, it cannot be used directly as an epitaxial template in conventional growth processes. To achieve ACSi film growth on such an amorphous substrate, we first grow an ionbeam-assisted deposition (IBAD) textured buffer layer that is biaxially-oriented (i.e., with preferred out-of-plane and in-plane crystallographic orientations); this layer in turn serves as a crystalline template for the growth of subsequent epitaxial buffer layers and ACSi films. With improving crystalline quality, such ACSi films show enhanced majority carrier mobility and improved minority carrier lifetime. EXPERIMENTAL DETAILS In the IBAD texturing process,1,2 an off-normal ion beam establishes biaxially-oriented grains of a growing film of certain materials on a non-single-crystalline substrate, thus establishing a highly crystalline template for the epitaxial growth of subsequent layers. The details of the IBAD texturing process are still not well understood,1,3,4 although some computational and analytical modeling work has been done in the area of ion-atom interactions and their effect on texture formation.5,6 We have previously reported our work on the preparation of ACSi films on metal tapes using an IBAD textured buffer layer.7,8,9 In this letter, we extend our work to glass substrates, and expand our device fabrication and characterization studies to include thin-film diodes and their electrical characteristics. Various alternative approaches to obtain crystalline Si on glass have also been extensively explored by other research groups.10,11,12,13
In this study, all deposited layers were electron-beam (e-beam) evaporated in situ on 0.5mm-thick glass substrates that were cut in 1 cm x 1 cm squares. The substrates were commercially-obtained
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