Graphene assisted III-V epitaxy towards substrate recycling

TL;DR

This paper explores a graphene-assisted epitaxial process on GaAs substrates to enable substrate recycling for cost reduction in high-efficiency III-V solar cells, demonstrating improved GaAs layer quality through patterned graphene and two-step growth.

Contribution

It introduces a novel graphene patterning and epitaxial growth method to facilitate substrate reuse and improve GaAs layer quality in solar cell fabrication.

Findings

Pattern orientation affects GaAs morphology and quality.

Optimal pattern orientation along [1__10]+22.5° yields smooth GaAs layers.

Achieved GaAs surface roughness reduced to 3.3 nm.

Abstract

Re-using the substrate is identified as a method for reducing the cost of high efficiency III-V solar cells. The approach investigated here consists in inserting a graphene layer onto a (001)GaAs substrate prior to the epitaxial growth of GaAs. To obtain a monocrystalline GaAs grown layer, the graphene layer is patterned, followed by a two-step epitaxial growth, here performed by molecular beam epitaxy (MBE). The first step is a selective area growth of GaAs in graphene openings, followed by a lateral overgrowth, under a modulated Ga flux. The second step, after reaching coalescence, consists in a regular growth under continuous Ga supply. It is observed that the pattern orientations relative to the crystallographic direction of the GaAs substrate below the graphene have an influence on GaAs morphology and quality. The best result was obtained for patterns oriented along [1__10]+22.5{\textdegree} with a graphene coverage of 50%, with a significantly reduced roughness down to 3.3 nm.