Development of germanium-on-germanium engineered substrates for III-V multijunction solar cells

Courtois, Guillaume; Kurstjens, Rufi; Cho, Jinyoun; Dessein, Kristof; García, Iván; Rey‐Stolle, Ignacio; Algora, Carlos; Depauw, Valérie; Porret, Clément; Loo, Roger

doi:10.1109/pvsc45281.2020.9300462

Cited by 6 publications

(6 citation statements)

References 6 publications

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“…Typical surfaces are almost one order of magnitude rougher than an unprocessed epi‐ready Ge wafer (~2 nm RMS for GeON vs. 0.2 nm RMS for epi‐ready wafer). However, this type of roughness was previously found to be compatible with III–V epitaxy 11,20 . Furthermore, the amplitude and granularity of this waviness are significantly smoothened out by the layer thickening in the present conditions, reaching ~0.7 nm RMS (Figure 12a–c).…”

Section: From 1‐μm Up To 30‐μm‐thick Geon Foil With High Growth‐rate ...supporting

confidence: 67%

“…However, this type of roughness was previously found to be compatible with III-V epitaxy. 11,20 Furthermore, the amplitude and granularity of this waviness are significantly smoothened out by the layer thickening in the present conditions, reaching $0.7 nm RMS (Figure 12a-c). At the F I G U R E 9 SIMS depth profiles of a boron-doped 10.5-μm-thick epitaxial layer grown on a gallium-doped GeON wafer.…”

Section: Epitaxial Ge Foil Qualitymentioning

confidence: 61%

“…Detached GeON foils of a few mm 2 were reported in 2019 by Park et al 10 In 2020, 2.5 cm × 2.5 cm detached areas were demonstrated by Courtois et al 11 Solar cells were fabricated in 2021 but only on non‐detachable GeON surfaces 17 . The next step is upscaling beyond 100‐ and 150‐mm‐diameter wafers (the common wafer dimensions for the space PV industry), and for which two hurdles are faced.…”

Section: From Ge Wafer To Wafer‐scale Detachable Ge Foilmentioning

confidence: 99%

“…Two routes of porous germanium are currently under development, based on random mesopores or patterned macropores. The former is usually referred to as “porous Ge” and the latter as “GON” or “GeON.” 10,11 Porous Ge is fabricated by electrochemical etching and is potentially the lower cost route 12,13 . The GeON structure involves lithography and dry etching but provides easier control on the detachment layer and seed surface morphology.…”

Section: Introductionmentioning

confidence: 99%

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

Depauw

Porret

Moelants

et al. 2022

Progress in Photovoltaics

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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 is 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 macroporous 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. By introducing a new high growth‐rate epitaxy process from GeCl4, and by engineering the GeON structure to introduce pillars with ad hoc density and shape, we fabricated P‐type foils with tunable boron doping up to 15 μm in thickness and 11 cm × 11 cm in area, for which the detachment strength could be adapted to the stresses induced by the solar cell process steps. The surface roughness and the electrical and crystal qualities of these foils were inspected by AFM, SIMS, SRP, ECCI, and TEM to check the GeCl4‐based epitaxy conditions and to check that the ad hoc pillars were not introducing any damage. Small‐area triple‐junction lattice‐matched GaInP/GaInAs/Ge solar cells were fabricated on 7‐μm‐thick Ge foils with various pillar densities and on a standard reference Ge wafer. The III–V layer nucleation was virtually the same on both substrates and the solar cells on the GeON foils performed in the same way as the cells on the Ge wafer, albeit a small loss in short‐circuit current and open‐circuit voltage that can be attributed to the thickness reduction and absence of rear‐side passivation. We conclude that it is possible to gain control on the GeON detachability and upscale the concept to areas relevant for the space PV industry, proving that porous germanium is a serious candidate for replacement of bulk Ge wafers in view of a more sustainable multijunction solar cell process.

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Section: From 1‐μm Up To 30‐μm‐thick Geon Foil With High Growth‐rate ...supporting

confidence: 67%

Section: Epitaxial Ge Foil Qualitymentioning

confidence: 61%

Section: From Ge Wafer To Wafer‐scale Detachable Ge Foilmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Depauw

Porret

Moelants

et al. 2022

Progress in Photovoltaics

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“…The GeON scheme can be extended to (defect free) bulk Ge for which the fabrication of GeON followed by layer transfer has recently been demonstrated. 18,27 The latter approach is limited to 200 mm wafer dimensions (which is the maximum size of available Ge substrates) while the work discussed in this manuscript can be extended to 300 mm wafer dimensions. Finally, it is noted that, although it was not done in this work, an additional Ge epitaxy on top of the GeON template can be considered to adapt the thickness of the Ge foil.…”

Section: Discussionmentioning

confidence: 99%

Epitaxial Ge-on-Nothing and Epitaxial Ge on Si-on-Nothing as Virtual Substrates for 3D Device Stacking Technologies

Loo

Porret

Han

et al. 2021

ECS J. Solid State Sci. Technol.

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Two new templates for strain-relaxed detachable Ge are introduced. The first one is based on epitaxial growth of Ge on a Si-on-Nothing (SiON) platform while the second consists of Ge-on-Nothing (GeON). The SiON and GeON templates are obtained from the reorganization of macro-porous Si and Ge, respectively, fabricated on regular Si substrates using conventional lithography, dryetching and annealing routines. Both templates contain similar densities of threading dislocations as typically obtained for conventional strain relaxed epitaxial Ge grown on bulk Si. In the GeON case, the excess carrier lifetime (32 ns) as extracted from time-resolved photoluminescence was > 4 times higher than the values measured for Ge grown on bulk Si with a similar thickness of the Ge layer. Both templates can be considered for novel device applications relying on thin Ge films and as starting material for layer transfer and 3-dimensional device stacking technologies, provided that a successful detachment from the parent substrate can be demonstrated. The reduction of non-radiative electron-hole recombinations makes the GeON also attractive for the fabrication of optical devices used in the fields of communication and imagers, such as Ge photodetectors and modulators, as lower dark currents are expected.

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Overview of Engineered Germanium Substrate Development for Affordable Large-Volume Multijunction Solar Cells

Cho,

Depauw,

Chapotot

et al. 2024

IEEE J. Photovoltaics

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Development of germanium-on-germanium engineered substrates for III-V multijunction solar cells

Cited by 6 publications

References 6 publications

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

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

Epitaxial Ge-on-Nothing and Epitaxial Ge on Si-on-Nothing as Virtual Substrates for 3D Device Stacking Technologies

Overview of Engineered Germanium Substrate Development for Affordable Large-Volume Multijunction Solar Cells

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