Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth
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NANO EXPRESS
Open Access
Tuning of strain and surface roughness of porous silicon layers for higher-quality seeds for epitaxial growth Marwa Karim1,2,3,4*, Roberto Martini2,4, Hariharsudan Sivaramakrishnan Radhakrishnan2,4, Kris van Nieuwenhuysen2, Valerie Depauw2, Wedgan Ramadan3, Ivan Gordon2 and Jef Poortmans2,4,5
Abstract Sintered porous silicon is a well-known seed for homo-epitaxy that enables fabricating transferrable monocrystalline foils. The crystalline quality of these foils depends on the surface roughness and the strain of this porous seed, which should both be minimized. In order to provide guidelines for an optimum foil growth, we present a systematic investigation of the impact of the thickness of this seed and of its sintering time prior to epitaxial growth on strain and surface roughness. Strain and surface roughness were monitored in monolayers and double layers with different porosities as a function of seed thickness and of sintering time by high-resolution X-ray diffraction and profilometry, respectively. Unexpectedly, we found that strain in double and monolayers evolves in opposite ways with respect to layer thickness. This suggests that an interaction between layers in multiple stacks is to be considered. We also found that if higher seed thickness and longer annealing time are to be preferred to minimize the strain in double layers, the opposite is required to achieve smoother layers. The impact of these two parameters may be explained by considering the morphological evolution of the pores upon sintering and, in particular, the disappearance of interconnections between the porous seed and the bulk as well as the enlargement of pores near the surface. An optimum epitaxial growth hence calls for a trade-off in seed thickness and annealing time, between minimum-strained layers and rougher surfaces. Keywords: Porous silicon; Strain; Surface roughness; Epitaxial growth; Layer-transfer process; Annealing time; Low-porosity layer; Seed layer; High-porosity layer PACS codes: 81.40.-z Treatment of materials and its effects on microstructure, nanostructure, and properties; 81.05. Rm Porous materials; granular materials; 82.80.Ej X-ray, Mössbauer and other γ-ray spectroscopic analysis methods
Background Nowadays, about 30% of the cost of a wafer-based silicon solar cell is due to the silicon material itself. Thus, researchers are aiming at reducing the consumption of silicon while keeping the cell efficiency high. One of these attempts is employing a layer-transfer process (LTP) where an active silicon layer is epitaxially grown using chemical vapor deposition (CVD) on porous silicon (PSi), which acts as the detachment layer and as the epitaxy-seed layer * Correspondence: [email protected] 1 KACST-Intel Consortium Center of Excellence in Nano-manufacturing Applications (CENA), Riyadh 11442, KSA 2 Interuniversity Microelectronics Center (IMEC), Kapeldreef 75, Leuven 3001, Belgium Full list of author information is available at the end of the article
[1,2]. Transferring the epitaxial layer
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