Free-carrier effects and optical phonons in GaNAs/GaAs superlattice heterostructures measured by infrared spectroscopic ellipsometry

Citation
J. Sik et al., Free-carrier effects and optical phonons in GaNAs/GaAs superlattice heterostructures measured by infrared spectroscopic ellipsometry, MRS I J N S, 5(3), 2000, pp. 1-8
Citations number
28
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Apllied Physucs/Condensed Matter/Materiales Science
Journal title
MRS INTERNET JOURNAL OF NITRIDE SEMICONDUCTOR RESEARCH
ISSN journal
1092-5783 → ACNP
Volume
5
Issue
3
Year of publication
2000
Pages
1 - 8
Database
ISI
SICI code
1092-5783(2000)5:3<1:FEAOPI>2.0.ZU;2-I
Abstract
The infrared-optical properties of GaAs/GaNxAs1-x superlattice (SL) heteros tructures (0 < x < 3.3%) are studied by variable angle-of-incidence infrare d spectroscopic ellipsometry (IRSE) for wavenumbers from 250 cm(-1) to 700 cm(-1). The undoped SL structures where grown on top of a 300 nm thick undo ped GaAs buffer layer on Te-doped (001) GaAs substrates by metal-organic va por phase epitaxy (MOVPE). We observe the well-known Berreman-polariton eff ect within the GaAs LO-phonon region. We further observe a strong polariton -like resonance near the coupled longitudinal-optical plasmon-phonon freque ncy of the Te-doped substrate at 306 cm(-1). For analysis of the IRSE data we employ the harmonic oscillator dielectric function model and the Drude m odel for free-carrier response. The additional resonance feature is explain ed by pseudo surface polariton (PSP) interface modes between the Te-doped G aAs and the undoped GaAs buffer layer/SL film. We find that the PSP modes a re extremely sensitive to free-carrier properties within the SL structures, and we obtain a strong increase in free-carrier concentration within the G aNAs SL sublayers with increasing x from analysis of the IRSE data. We furt her observe the localized vibrational modes of nitrogen at 470 cm(-1) in th e GaNxAs1-xSL sublayers with a polar strength that increases linearly with x, and which can be used to monitor the nitrogen concentration in GaNxAs1-x .