Spin Accumulation in Nondegenerate and Heavily Doped p-Type Germanium

TL;DR

This study investigates spin accumulation in p-type germanium with varying hole concentrations, revealing unexpected trends and significantly larger spin signals in heavily doped samples compared to theoretical predictions.

Contribution

It demonstrates that spin accumulation increases with doping level in p-type germanium, contrary to existing theories, and rules out interface effects as the cause.

Findings

Spin accumulation is smallest at low doping levels.

Heavily doped germanium shows much larger spin signals than predicted.

Contacts are free of rectification and Schottky barriers across doping levels.

Abstract

Spin accumulation induced in p-type germanium from Fe/MgO tunnel contacts is studied as a function of hole concentration p (10^16 - 10^19 cm-3). For all p, the contacts are free of rectification and Schottky barrier, guaranteeing spin injection into the Ge and preventing spin accumulation enhancement by two-step tunneling via interface states. The observed spin accumulation is smallest for nondegenerate doping (p ~ 10^16 cm-3) and increases for heavily doped Ge. This trend is opposite to what is expected from spin injection and diffusion theory. For heavily doped Ge, the observed spin accumulation is orders of magnitude larger than predicted.