Wafer‐scale Ge epitaxial foils grown at high growth rates and released from porous substrates for triple‐junction solar cells

• DOI: 10.1002/pip.3634
• Publication Date: 2022-11-09T02:20:50Z
• Authors: Valérie Depauw; Clément Porret; Myriam Moelants; Emma Vecchio; Koen Kennes; Han Han; Roger Loo; Jinyoun Cho; Guillaume Courtois; Rufi Kurstjens; Kristof Dessein; Víctor Orejuela; Clara Sanchez‐Perez; Ignacio Rey‐Stolle; Iván García
• Keywords: germanium; lift-off; epitaxy; 0202 electrical engineering, electronic engineering, information engineering; 02 engineering and technology; 7. Clean energy; multijunction solar cells

Abstract Germanium is listed as a critical raw material, and for environmental economic sustainability reasons, strategies lower consumption must be implemented. A promising approach Ge lift‐off concepts, which enable to re‐use the substrate multiple times. Our concept based on Ge‐on‐Nothing that controlled restructuring at high temperature of macroporous surface, forming foil weakly attached its parent wafer. Its suitability III–V epitaxy seed support has previously been demonstrated with proof‐of‐concept solar cells. This work focuses bringing this next level, by upscaling detachable area full 200‐mm wafer scale, increasing thickness sufficient light absorption in bottom cell, improving control strength bonding suspended parent. By introducing new growth‐rate process from GeCl 4 , engineering GeON structure introduce pillars ad hoc density shape, we fabricated P‐type foils tunable boron doping up 15 μm 11 cm × area, detachment could adapted stresses induced cell steps. The surface roughness electrical crystal qualities these were inspected AFM, SIMS, SRP, ECCI, TEM check ‐based conditions not any damage. Small‐area triple‐junction lattice‐matched GaInP/GaInAs/Ge cells 7‐μm‐thick various pillar densities standard reference layer nucleation was virtually same both substrates performed way wafer, albeit small loss short‐circuit current open‐circuit voltage can attributed reduction absence rear‐side passivation. We conclude it possible gain detachability upscale areas relevant space PV industry, proving porous germanium serious candidate replacement bulk wafers view more sustainable multijunction process.