Lateral Mn$_5$Ge$_3$ spin-valve in contact with a high-mobility Ge two-dimensional hole gas

Ge two-dimensional hole gases (2DHG) in strained modulation-doped quantum-wells represent
a promising material platform for future spintronic applications due to their excellent spin
transport properties and the theoretical possibility of efficient spin manipulation. Due to the
continuous development of epitaxial growth recipes extreme high hole mobilities and low
effective masses can be achieved, promising an efficient spin transport. Furthermore,
the Ge 2DHG can be integrated in the well-established industrial complementary
metal-oxide-semiconductor (CMOS) devices technology. However, efficient electrical spin
injection into a Ge 2DHG—an essential prerequisite for the realization of spintronic
devices—has not yet been demonstrated. In this work, we report the fabrication and
low-temperature magnetoresistance (MR) measurements of a laterally structured Mn$_5$Ge$_3$/Ge
2DHG/ Mn$_5$Ge$_3$ device. The ferromagnetic Mn$_5$Ge$_3$ contacts are grown directly into the Ge
quantum well by means of an interdiffusion process with a spacing of approximately 130 nm,
forming a direct electrical contact between the ferromagnetic metal and the Ge 2DHG. ... mehrHere, we
report for the first time a clear MR signal for temperatures below 13 K possibly arising from
successful spin injection into the high mobility Ge 2DHG. The results represent a step forward
toward the realization of CMOS compatible spintronic devices based on a 2DHG.