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Evidence from EELS of Oxygen in the Nucleation Layer of a MBE grown III-N HEMT

Published online by Cambridge University Press:  03 September 2012

Tyler J. Eustis ,
John Silcox ,
Michael J. Murphy  and
William J. Schaff
Tyler J. Eustis
Affiliation:
Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853
John Silcox
Affiliation:
School of Applied Engineering Physics, Cornell University, Ithaca, NY 14853
Michael J. Murphy
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY 14853
William J. Schaff
Affiliation:
School of Electrical Engineering, Cornell University, Ithaca, NY 14853
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Abstract

The presence of oxygen throughout the nominally AlN nucleation layer of a RF assisted MBE grown III-N HEMT was revealed upon examination by Electron Energy Loss Spectroscopy (EELS) in a Scanning Transmission Electron Microscope (STEM). The nucleation layer generates the correct polarity (gallium face) required for producing a piezoelectric induced high mobility two dimensional electron gas at the AlGaN/GaN heterojunction. Only AlN or AlGaN nucleation layers have provided gallium face polarity in RF assisted MBE grown III-N's on sapphire. The sample was grown at Cornell University in a Varian GenII MBE using an EPI Uni-Bulb nitrogen plasma source. The nucleation layer was examined in the Cornell University STEM using Annular Dark Field (ADF) imaging and Parallel Electron Energy Loss Spectroscopy (PEELS). Bright Field TEM reveals a relatively crystallographically sharp interface, while the PEELS reveal a chemically diffuse interface. PEELS of the nitrogen and oxygen K-edges at approximately 5-Angstrom steps across the GaN/AlN/sapphire interfaces reveals the presence of oxygen in the AlN nucleation layer. The gradient suggests that the oxygen has diffused into the nucleation region from the sapphire substrate forming this oxygen containing AlN layer. Based on energy loss near edge structure (ELNES), oxygen is in octahedral interstitial sites in the AlN and Al is both tetrahedrally and octahedrally coordinated in the oxygen rich region of the AlN.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 595: Symposium W – GaN and Related Alloys - 1999 , 1999 , F99W3.31
Copyright
Copyright © Materials Research Society 1999

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