Reuse of GaAs substrates for epitaxial lift-off by employing protection layers

Abstract

We demonstrate repeated use of GaAs wafers for multiple growths by employing lattice-matched epitaxial protection layers to preserve the wafer surface in its original condition following their etch removal after growth. The protection layers provide a regrowth surface that eliminates the need for repolishing prior to subsequent growth. Between growths, the protection layers are removed by wet chemical etching. The resulting surface quality is examined using atomic force microscope and energy dispersive spectrometry. We show that the surface roughness, chemical composition, morphology, and electronic properties of the GaAs surface after protection-layer removal are comparable to that of the original substrate surface. We show that p-n junction GaAs solar cells grown on original and reused wafers have nearly identical performance with power conversion efficiencies of ∼23%, under simulated 1 sun illumination, AM1.5 G. The high power conversion efficiency of GaAs solar cells combined with reduced costs associated with multiple parent wafer reuses promise cost competitiveness with incumbent solar cell technologies.

Transforming the cost of solar-to-electrical energy conversion: Integrating thin-film GaAs solar cells with non-tracking mini-concentrators

“…9 The previously described ND-ELO method employs epitaxial protective layers grown between the sacrificial layer and the wafer that completely preserve the original wafer surface quality, even at the atomic scale, during the ELO process. 9,10 Selective removal of the protective layers using wet chemical etching eliminates the need for the chemomechanical polishing used in conventional ELO. Therefore, ND-ELO allows for the nearly indefinite reuse of the GaAs substrates, converting their cost from a material expense into a capital investment.…”

“…[5][6][7][8] However, the cost reduction long promised by the epitaxial lift-off (ELO) process has primarily been limited by the inability to fully recover the original wafer surface quality after each growth, leading to a limited number of times that the substrate can be recycled due to the accumulation of defects and to wafer thinning incurred by chemo-mechanical polishing. [9][10][11][12][13] Furthermore, high PCE alone does not necessarily translate into low-cost solar energy production when expensive active materials and fabrication processes are used in their manufacture. As an alternative to simply improving PCE, solar concentrators have been demonstrated as a means for reducing the use of costly active solar cell materials.…”

Epitaxial lift-off process for gallium arsenide substrate reuse and flexible electronics

“…However, the remaining contaminants still seriously degrade the quality of regrown films and device performances 9 . To completely remove all these contaminants and achieve high quality regrown films, multi-step chemical polishing with different sacrificial (protection) layers was recently proposed, with the penalties of the higher cost for extra epitaxial growths and HF still being used as the main etchant 19 .…”

GaAs solar cell on Si substrate with good ohmic GaAs/Si interface by direct wafer bonding

“…However, we note that the aim of our work is to show a good crystal quality of the cell layer and a good electrical connection between the GaAs and Si after the wafer bonding with a cost-effective method, which is the key issue in using bonding techniques for commercial applications. Furthermore, combing the developed wafer bonding and epitaxial lift off techniques [26][27][28], further cost reduction is expected and an increasing cell performances at the same time.…”