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Stress Gradients In Heteroepitaxial Gallium Nitride Films

Published online by Cambridge University Press:  10 February 2011

J. W. Ager III ,
G. Conti ,
L. T. Romano  and
C. Kisielowski
J. W. Ager III
Affiliation:
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
G. Conti
Affiliation:
Materials Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720
L. T. Romano
Affiliation:
Xerox PARC, 3333 Coyote Hill Rd., Palo Alto, CA 94306
C. Kisielowski
Affiliation:
Materials Sciences and Mineral Engineering Department, University of California at Berkeley, Berkeley, CA 94720
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Abstract

Heteroepitaxial GaN films grown on sapphire are usually in a compressive residual biaxial stress state that is typically 100 – 500 MPa but can be as high as 1 GPa. Spatially resolved measurements of GaN film stresses obtained via micro-Raman spectroscopy using shifts in the frequency of the E2 phonon are presented. The spatial resolution of this stress measurement technique is ca. 2 μm laterally and 10 μm in the axial (growth) direction. Two interesting stress gradients are found near cleaved edges. (1) On the surface of the cleaved edge the compressive film stress is a maximum at the GaN/sapphire interface and relaxes to a nearly stress-free state towards the free edge. (2) In the lateral direction, the stress increases away from the edge, reaching a steady-state value at approximately 10x the film thickness. It is shown that the effects are consistent with existing finite element models used to treat strained growth of surface structures in other semiconductor systems. An axial stress gradient that is not associated with edge effects is found in some thick (>20 μm) HVPEgrown films. The interface region is found to be up to 500 MPa in compression, but this stress declines toward the film surface, which is found to be nearly stress free.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 482 , 1997 , 769
Copyright
Copyright © Materials Research Society 1998

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