Al–Ge-paste-induced liquid phase epitaxy of Si-rich SiGe(111) for epitaxial Co-based Heusler alloys

For high-performance spintronic applications with Co-based Heusler alloys, we explore Si1−xGex(111) grown by liquid phase epitaxy (LPE) with Al–Ge mixed paste, where x is the Ge content. By annealing the screen printed Al–Ge paste on a Si(111) substrate, a continuous Si1−xGex(111) layer with a smooth interface between the Si1−xGex layer and Si substrate is epitaxially grown. The surface with residual paste is polished and treated by chemical mechanical polishing and a catalyst referred etching (CARE) process, resulting in a reduction of the root-mean-square roughness to 0.52 nm over a large-scale area. After the surface treatments of the LPE-Si1−xGex, we can obtain Si0.93Ge0.07(111) to epitaxially grow one of the Co-based Heusler alloys, Co2FeSi. The magnetic properties and intermixing at the Co2FeSi/LPE-Si0.93Ge0.07(111) interface are consistent with those at the Co2FeAl0.5Si0.5/Si(111) and the Co2FeAl0.5Si0.5/Ge(111) interfaces. The Al–Ge-paste-induced LPE-Si1−xGex(111) and the CARE process for the surface are quite effective for the growth of Co-based Heusler alloys in future SiGe-based spintronic devices.