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Optical Phonons in Hexagonal Al x In y Ga 1– x – y N ( y ≈ 0.12)
Author(s) -
Kasic A.,
Schubert M.,
Off J.,
Scholz F.,
Einfeldt S.,
Hommel D.
Publication year - 2002
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/1521-3951(200212)234:3<970::aid-pssb970>3.0.co;2-4
Subject(s) - phonon , materials science , hexagonal crystal system , metalorganic vapour phase epitaxy , plasmon , condensed matter physics , absorption (acoustics) , optoelectronics , crystallography , chemistry , nanotechnology , physics , layer (electronics) , epitaxy , composite material
We report on first studies of the phonon mode properties of hexagonal Al x In y Ga 1— x — y N films. The 200–330 nm thick quaternary films (0 ≤ x ≤ 0.40, y ≈ 0.12), grown by MOCVD on 6H‐SiC substrates, are pseudomorphically strained to the GaN buffer layers. We observe and differentiate the influence of strain and alloying on the frequency of the GaN‐like E 1 (TO) phonon mode of Al x In y Ga 1— x — y N using infrared spectroscopic ellipsometry. Assuming the effective electron mass value of GaN, the free‐electron concentrations are estimated from the A 1 ‐LO‐phonon–plasmon coupled mode frequencies and increase by about two orders of magnitude in going from x = 0 to x = 0.40. We further obtain the composition dependence of the polarity for the AlN‐like phonon mode with E 1 symmetry. A possibly disorder‐induced absorption band occurs above the GaN‐like E 1 (TO) mode.