Phonons and Free Carriers in a Strained Hexagonal GaN-AlN Superlattice Measured by Infrared Ellipsometry and Raman Spectroscopy
This article was presented as part of Symposium W, "Gallium Nitride and Related Alloys" at the 1999 Fall Meeting of the Materials Research Society held in Boston, Massachusetts, November 28-December 3
Abstract
Phonon and free-carrier effects in a strained hexagonal ( 
) {GaN}l-{AlN}m
superlattice (SL) heterostructure (l = 8 nm, m = 3 nm) are studied by infrared
spectroscopic ellipsometry (IRSE) and micro (µ)-Raman scattering. Growth of the
heterostructures was performed by metal-organic vapor phase epitaxy (MOVPE) on
(0001) sapphire. An unstrained 1 µm-thick -GaN layer was deposited prior to the SL. SL
phonon modes are identified combining results from both IRSE and µ-Raman techniques.
The shift of the GaN-sublayer phonon modes is used to estimate an average compressive
SL stress of 
xx ~ - 4.3 GPa. The IRSE data reveal a free-carrier concentration of ne ~
5x1018 cm-3 within the undoped SL GaN-sublayers. According to the vertical carrier
confinement, the free-carrier mobility is anisotropic, and the lateral mobility ( µ
~ 400
cm2/Vs, polarization E c-axis) exceeds the vertical mobility ( µ|| ~ 24 cm2/Vs, E||c) by one
order of magnitude.
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Cite this article as: MRS Internet J. Nitride Semicond. Res. 5S1, W11.39 (2000).
last updated Wednesday, May 17, 2000 4:59:49 PM.
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