Eur. Phys. J. B (2013) 86: 140
https://doi.org/10.1140/epjb/e2013-31067-7

Regular Article

Transition from spin accumulation into interface states to spin injection in silicon and germanium conduction bands^*

¹ INAC/SP2M, CEA and Université Joseph Fourier, 38054 Grenoble, France
² Unité Mixte de Physique, CNRS and Thalès, 91767 Palaiseau, France
³ LETI, CEA Minatec Campus, 38054 Grenoble, France
⁴ INAC/SCIB, CEA and Université Joseph Fourier, 38054 Grenoble, France

^a e-mail: matthieu.jamet@cea.fr

Received: 22 November 2012
Received in final form: 20 December 2012
Published online: 8 April 2013

Abstract

Electrical spin injection into semiconductors paves the way for exploring new phenomena in the area of spin physics and new generations of spintronic devices. However the exact role of interface states in the electrical spin injection mechanism from a magnetic tunnel junction into a semiconductor is still under debate. Here we demonstrate a clear transition from spin accumulation into interface states to spin injection in the conduction band of n-Si and n-Ge using a CoFeB/MgO tunnel contact. We observe spin signal amplification at low temperature due to spin accumulation into interface states followed by a clear transition towards spin injection in the conduction band from approximately 150 K up to room temperature. In this regime, the spin signal is reduced down to a value compatible with the standard spin diffusion model. More interestingly, in the case of germanium, we demonstrate a significant modulation of the spin signal by applying a back-gate voltage to the conduction channel. We also observe the inverse spin Hall effect in Ge by spin pumping from the CoFeB electrode. Both observations are consistent with spin accumulation in the Ge conduction band.