Effects of post bonding annealing on GaAs//Si bonding interfaces and its application for sacrificial-layer-etching based multijunction solar cells

• Published in: Solar energy materials and solar cells 2020-06, Vol.210, p.110501, Article 110501
• Main Authors: Shigekawa, Naoteru, Kozono, Ryo, Yoon, Sanji, Hara, Tomoya, Liang, Jianbo, Yasui, Akira
• Format: Article
• Language: English
• Subjects: Aluminum; Aluminum fluorides; Annealing; Bonding; Electrical measurement; Epitaxial lift-off; Etching; GaAs//Si double junction cells; Interfaces; Low temperature; Low temperature annealing; Oxygen atoms; Photoelectric emission; Photoelectron spectroscopy; Photoelectrons; Photovoltaic cells; Sacrificial layer etching; Silicon substrates; Solar cells; Spectroscopy; Spectrum analysis; Substrates; Surface activated bonding; X ray photoelectron spectroscopy
• ISSN: 0927-0248; 1879-3398
• DOI: 10.1016/j.solmat.2020.110501

By using the sacrificial layer (SL) etching, GaAs substrates are separated from III–V epi substrate//Si substrate junctions that are made by surface activated bonding (SAB) technologies. The post-bonding low-temperature (300-∘C) annealing plays an essential role in achieving a promising (∼90%) bonding yield. The effects of the post-bonding annealing are investigated by hard X-ray photoemission spectroscopy and current–voltage measurements of GaAs//Si bonding interfaces. It is found that the concentration of oxygen atoms at interfaces is reduced and the resistance decreases to 1.6–2.1 mΩcm2 by the low-temperature annealing. Aluminum fluoride complexes are not observed by X-ray photoelectron spectroscopy on the exposed surfaces of separated GaAs substrates. The roughness average of the surfaces is ≈0.25–0.30 nm. The characteristics of double junction cells fabricated on the GaAs//Si junctions prepared by the SL etching are almost the same as those of cells fabricated by dissolving GaAs substrates after bonding. These results indicate that multijunction cells could be fabricated in a process sequence compatible with reuse of GaAs substrates by combining the SL etching and SAB. •III–V//Si junctions with a ∼90% of bonding yield is achieved in III–V//Si junctions prepared by direct wafer bonding and subsequent epitaxial lift-off.•A post-bonding annealing plays an essential role in realizing interfaces with an enough tolerance against HF-based solution for sacrificial layer etching.•The epitaxial lift-off process causes no influence on performances of MJ cells.