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Growth of tetragonal Si via plasma-enhanced epitaxy Wanghua Chen, Gwenaelle Hamon, Ronan Leal, JeanLuc Maurice, Ludovic Largeau, and Pere Roca i Cabarrocas Cryst. Growth Des., Just Accepted Manuscript • Publication Date (Web): 28 Jun 2017 Downloaded from http://pubs.acs.org on June 28, 2017
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Crystal Growth & Design
Growth of tetragonal Si via plasma-enhanced epitaxy Wanghua Chen†‡*, Gwenaëlle Hamon†§, Ronan Léal†‡§, Jean-Luc Maurice†, Ludovic Largeauǁ, and Pere Roca i Cabarrocas†‡ †LPICM, CNRS, Ecole Polytechnique, Université Paris-Saclay, 91128 Palaiseau, France ‡IPVF (Institut Photovoltaïque d’Ile-de-France), 92160 Antony, France §
Total SA, Tour Michelet, 92069 Paris La Défense, France
ǁC2N, CNRS, Université Paris-Sud, Université Paris-Saclay, 91460 Marcoussis, France
ABSTRACT We have been able to synthesize directly the tetragonal Si by low temperature plasmaenhanced chemical vapor deposition using hydrogen and silane as precursor and carrier gas, respectively. With the optimization of growth conditions, a stable tetragonal epitaxial Si can be grown on crystalline Si substrate at large scale. By combining X-ray diffraction and high resolution transmission electron microscopy measurements, we found that the epitaxial layer has smaller in-plane but larger out-of-plane lattice parameters as compared to the crystalline substrate. The existence of hydrogen platelets in epitaxy is also observed, which affects the diffraction patterns along that direction. We attribute the formation of tetragonal Si is due to the hydrogenated-cluster-assisted epitaxy. Other possible reasons including host sites of hydrogen atoms and thermal expansion coefficients are also discussed.
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Crystal Growth & Design
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INTRODUCTION Silicon is widely used in microelectronics and photovoltaics due to its abundance on earth (the second abundant element) and nontoxicity in its bulk form.1,
2
Exploring other
phases than diamond cubic for Si has always attracted lots of attention since the properties of Si such as bandgap and absorption are related to the specific phase.3, 4 Up to now, a total of 32 phases of Si have been observed or predicted.5 The thermodynamically stable structure of Si is diamond cubic (Si-I). However, its structure can be changed to other phases depending on pressure,5 for example, tetragonal (β-tin, Si-II) at pressure higher than 11.7 GPa, simple hexagonal (Si-V) beyond 15 GPa and orthorhombic (Si-VI) above 42 GPa. Besides the methods based on hyper high pressure and temperature with sub-millimeter size samples, other methods applied only to nano or micro areas are also developed. For example, at the nanoscale, polytypes of cubic Si including fcc and bc8 have been observed in Si nanocrystallites by plasma-enhanced chemical vapor deposition (PECVD),6 hexagonal Si nanoshells can be produced using Wurtzite nanowires as a template7 and hexagonal Si nanowires have been grown by Vapor Liquid Solid method.8, 9 As far as the tetragonal Si is considered, micro-deformation with indentation10 and micro-explosion with ultrafast laser4 have been used. Here, we developed a method to grow tetragonal Si on large areas (5×5 cm2) at low pressure (
