Interplay between the electrical transport properties of GeMn thin films and Ge substrates

TL;DR

This study reveals that substrate conduction significantly affects electrical transport measurements in GeMn thin films on Ge substrates, emphasizing the need to account for substrate effects to accurately interpret magnetic and transport properties.

Contribution

It demonstrates how substrate conduction influences transport measurements in GeMn thin films and proposes methods to mitigate this effect using n-type substrates.

Findings

Substrate conduction dominates transport measurements on high-resistivity Ge substrates.

Using n-type Ge substrates reduces substrate conduction effects.

Magneto resistance effects are negligible in films on n-type substrates.

Abstract

We present evidence that electrical transport studies of epitaxial p-type GeMn thin films fabricated on high resistivity Ge substrates are severely influenced by parallel conduction through the substrate, related to the large intrinsic conductivity of Ge due to its small bandgap. Anomalous Hall measurements and large magneto resistance effects are completely understood by taking a dominating substrate contribution as well as the measurement geometry into account. It is shown that substrate conduction persists also for well conducting, degenerate, p-type thin films, giving rise to an effective two-layer conduction scheme. Using n-type Ge substrates, parallel conduction through the substrate can be reduced for the p-type epi-layers, as a consequence of the emerging pn-interface junction. GeMn thin films fabricated on these substrates exhibit a negligible magneto resistance effect. Our study underlines the importance of a thorough characterization and understanding of possible substrate contributions for electrical transport studies of GeMn thin films.