Diffusion profiles of transition metals (TM= Co or Mn) in ZnO and GaN incorporated by annealing of thin TM film

Mac Mugumaoderha Cubaka 1Jacques A. Dumont Jacques Ghijsen 1Wolfgang Drube Bogdan J. Kowalski 2Cathérine Moisson 4Laurent Houssiau 1Robert Sporken 1,3

1. University of Namur (FUNDP), rue de Bruxelles 61, Namur 5000, Belgium
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. University of Illinois at Chicago, Chicago, Il 60607, United States
4. NOVASiC Savoie Technolac, Le Bourget du Lac 73375, France

Abstract

Injecting spin-polarized carriers electrically into a spintronic device remains a challenge that could be solved using Diluted Magnetic Semiconductors (DMS). Room temperature ferromagnetism can be achieved in DMS based on wide bandgap semiconductors (eg. GaN or ZnO). Nevertheless the structural and electronic properties of these wide bandgap DMS must be further studied in other to explain the origin of this ferromagnetic character.

The aim of this work was to investigate the structural and electronic properties of (Zn,TM)O and (Ga,TM)N layers obtained by thermal diffusion of thin films (≤ 2nm) of TM (TM = Mn or Co) into ZnO and GaN single crystals.

The samples were characterised in-situ by scanning tunnelling microscopy (STM), Auger electron spectroscopy (AES), low energy electron diffraction (LEED), High energy X-ray Photoemission Spectroscopy (XPS) and ex-situ by time of flight secondary ion mass spectroscopy (ToF-SIMS). The present abstract will mainly refer to AES results. From the evolution of the intensity of TM, Zn, O, Ga, and N Auger lines upon annealing, and thanks to modelling of the attenuation of Auger lines by matter we could describe the diffusion profile of TM into ZnO and GaN under various conditions. The results of the model were then compared to ToF-SIMS depth profiles.

Upon annealing, coalescence of the TM film into 3D islands is observed followed by diffusion and substitution.

In the case of TM/ZnO, the (Zn1-x,TMx)O layer is very thin (~6.6 nm), with x~0.5. According to High energy XPS on Co/ZnO system, at 800 K oxidation of Co into CoO is complete.

In case of the Mn/ZnO system, a Moiré structure is observed on the LEED pattern. From the Auger data, Mn seems to remain at the surface of ZnO in the form of a stable oxide layer.

For Mn/GaN, Ga atoms substituted by Mn segregate towards the surface. Annealing the system up to 910K induces formation of a (Ga0.8,TM0.2)N layer with thickness of ~ 18.6 nm.

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium B, by Mac Mugumaoderha Cubaka
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-19 15:29
Revised:   2009-06-07 00:44