Title:	How to Nicely Break Up? Engineering the Lift-Off of Tunable Epitaxial Germanium Foils for Multijunction Solar Cells
Author(s):	V. Depauw, C. Porret, R. Loo, M. Moelants, K. Kennes, E. Vecchio, H. Han, J. Cho, G. Courtois, R. Kurstjens, K. Dessein, I. Rey-Stolle, V. Orejuela, C. Sanchez-Perez, I. Garcia
Keywords:	Epitaxy, Germanium, Sustainable, Flexible Substrate, Space Cells
Topic:	Evolving and Emerging Technologies: Tandems; Thin Film absorbers; III-V; New Materials and Concepts; Advanced Modelling
Subtopic:	III-V and Related Compound Semiconductors
Event:	8th World Conference on Photovoltaic Energy Conversion
Session:	2DO.9.1
ISBN:	3-936338-86-8
Price:	0,00 EUR
Document(s):	presentation

Abstract/Summary:

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Germanium is listed as a critical raw material and, for environmental and economic sustainability reasons, strategies for lower consumption must be implemented. A promising approach are Ge lift-off concepts, which enable to re-use the substrate multiple times. Our concept is based on the Ge-on-Nothing approach that is the controlled restructuring at high temperature of a macro-porous Ge surface, forming a Ge foil weakly attached to its parent wafer. Its suitability as III-V epitaxy seed and support substrate has previously been demonstrated with proof-of-concept solar cells. This work focuses on bringing this concept to the next level, by upscaling the detachable area to a full 200-mm wafer scale, increasing foil thickness for sufficient light absorption in the Ge bottom cell, and improving the control on the strength that is bonding the suspended foil to its parent. The whole concept is then demonstrated with detachable small-area triple-junction lattice-matched GaInP/GaInAs/Ge solar cells, delivering the same performance as cells grown on standard Ge wafers.