Phonons and free carriers in a strained hexagonal GaN-AlN superlattice measured by infrared ellipsometry and Raman spectroscopy

M. Schubert, A. Kasic, T. E. Tiwald, J. A. Woollam, V. Härle, F. Scholz

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

Phonon and free-carrier effects in a strained hexagonal (α) {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 α-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 σxx ∼ - 4.3 GPa. The IRSE data reveal a free-carrier concentration of ne ∼ 5×10 18 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.

Original languageEnglish (US)
JournalMRS Internet Journal of Nitride Semiconductor Research
Volume5
Issue numberSUPPL. 1
DOIs
StatePublished - 2000

ASJC Scopus subject areas

  • Materials Science(all)

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