Selective patterning of single-crystal GaAs/Ge structures on Si substrates by molecular beam epitaxy

Abstract

Patterned single-crystal GaAs/Ge layers are grown on Si substrates by molecular beam epitaxy deposition through a bilayer mask. The ability to pattern device-quality GaAs structures on Si allows for integration of GaAs and Si devices on a monolithic chip. In this paper we describe the experimental details of a process that could be used to fabricate such circuits. The Si substrate, before growth, is patterned using a bilayer silicon nitride/silicon dioxide mask and conventional photolithographic techniques. During growth, in areas where the Si substrate is exposed, the GaAs/Ge layers grow epitaxially. After growth, a chemical etch is used that dissolves the mask, retaining the single-crystal GaAs/Ge pattern. The bilayer mask yields good pattern replication and prevents diffusion of Ga and As into the underlying Si devices, as shown by secondary ion mass spectroscopy data. The bilayer mask also aids in the lift-off process where thick GaAs/Ge layers are required and 100% lift-off yield is mandatory. Sample morphology and crystallinity are examined by scanning electron microscopy and reflection high-energy electron diffraction.