GaInP solar cells grown on Ge-on-Ge engineered substrates

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

doi:10.1109/pvsc43889.2021.9518407

Cited by 4 publications

(5 citation statements)

References 3 publications

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“…Detached GeON foils of a few mm 2 were reported in 2019 by Park et al 10 In 2020, 2.5 cm Â 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. The first, practical, hurdle is that the Ge foil dimensions are limited by the lithography and dry-etch tool resolution, uniformity, and reproducibility.…”

Section: Upscaling the Foil Areamentioning

confidence: 99%

“…Previously, we demonstrated GaInP solar cells on GeON wafers, but not yet detached solar cells. 17 For this purpose, the foil must feature a density of pillars that appropriately trades off ease of detachment (i.e., weak enough to be compatible with standard F I G U R E 3 Top-view SEM images at the location of two crystal-originated pits (COP) of the evolution of the GeON surface along the process, from the starting blanket surface up to pore reorganization. Only the large COP prevented pore formation, but both eventually led to an interruption in the detachment layer, a pillar.…”

Section: Controlling Detachabilitymentioning

confidence: 99%

“…The porous structure must result in a GeON wafer with an epi‐ready surface sufficiently resilient to be used as a Ge wafer equivalent for III–V heteroepitaxy. Previously, we demonstrated GaInP solar cells on GeON wafers, but not yet detached solar cells 17 . For this purpose, the foil must feature a density of pillars that appropriately trades off ease of detachment (i.e., weak enough to be compatible with standard bonding methods) and resistance to delamination (i.e., strong enough to withstand the mechanical stress from the ambient variations caused by, e.g., pressure, temperature, and from the foreign solar cell materials themselves).…”

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

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: Upscaling the Foil Areamentioning

confidence: 99%

Section: Controlling Detachabilitymentioning

confidence: 99%

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

confidence: 99%

See 1 more Smart Citation

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

Self Cite

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“…The current industrial standard for substrate reuse, epitaxial lift-off (ELO), has achieved some degree of substrate reuse, but further cost reduction is limited by low throughput of the lateral etching step and the periodic need for repolishing [2,9]. Alternative strategies for device lift-off and subsequent substrate reuse include controlled spalling [10], laser lift-off [11], multiple ELO [12], porous substrates [13][14][15][16][17], and remote epitaxy [18].…”

Section: Introductionmentioning

confidence: 99%

“…However, the faceted surface presents a challenge for the direct use of spalled substrates for the growth of high-efficiency III-V solar cells, which have traditionally employed flat epilayers. Other work has investigated solar cells on non-pristine growth surfaces [9,15,16,[25][26][27][28], and has observed that some morphological spalling defects diminish cell performance [29,30]. However, the impact, if any, of these particular faceted GaAs surfaces on the quality of subsequently grown materials and devices is unexplored.…”

Section: Introductionmentioning

confidence: 99%

Analysis of Crystalline Defects Caused by Growth on Partially Planarized Spalled (100) GaAs Substrates

et al. 2023

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We analyze the effect of growth on non-(100) surfaces resulting from incomplete planarization of spalled GaAs wafers on the defect structure of GaAs solar cell layers grown by hydride vapor phase epitaxy (HVPE). Controlled spalling of (100)-oriented GaAs has the potential to reduce substrate costs for III-V epitaxy; however, it creates regularly faceted surfaces that may complicate the growth of high-quality III-V optoelectronic devices. We leverage the anisotropic growth rate of HVPE to planarize these faceted GaAs substrates, reducing the surface roughness and degree of faceting. We observe degraded solar cell performance and material quality in sample areas where facets are not completely removed. We used dark lock-in thermography and photoluminescence to identify recombination in areas that were not fully planarized. We used cathodoluminescence to identify the presence of extended defects in these regions, which are correlated with bandgap fluctuations in the material. We hypothesize that these defects were created by strain from compositional fluctuations in ternary alloys grown on the faceted surfaces. This work elucidates the potential issues of solar cells grown on faceted surfaces and builds understanding toward realizing high performance III-V photovoltaics with the cost-reduction potential of controlled spalling.

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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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GaInP solar cells grown on Ge-on-Ge engineered substrates

Cited by 4 publications

References 3 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

Analysis of Crystalline Defects Caused by Growth on Partially Planarized Spalled (100) GaAs Substrates

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

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