Formation of Mn$_{5}$Ge$_{3}$ on a Recess-Etched Ge (111) Quantum-Well Structure for Semiconductor Spintronics

Ge two-dimensional hole gases (2DHG) formed in strained, modulation-doped quantum-wells are highly suitable for future spintronic applications due to their good electronic transport properties. For electrical spin injection into a Ge 2DHG, the ferromagnetic alloy Mn5Ge3 can be used as a contact material. The Mn5Ge3 layer can be grown as an interlayer by interdiffusion between an evaporated Mn layer and the Ge 2DHG. In this paper, we report on the growth of a ferromagnetic Mn5Ge3 thin film directly on the strained Ge. To this end, the Si20Ge80 capping layer covering the channel was selectively removed using Ar+ ion milling. We investigate the magnetic properties of Mn5Ge3 grown on a Ge (111) 2DHG by superconducting quantum interference device magnetometry and compare the results to an unetched Mn5Ge3 on Ge (111) reference. Furthermore, temperature-dependent Hall measurements using the Mn5Ge3 contacts on the Ge (111) 2DHG confirm the electrical contact to the high mobility 2DHG. These results are an important step towards electrical spin injection into a Ge 2DHG which is a promising material for future spintronic applications.