Band-gap energies, free carrier effects, and phonon modes in strained GaNAs/GaAs and GaNAs/InAs/GaAs superlattice heterostructures measured by spectroscopic ellipsometry
Identifieur interne : 010578 ( Main/Repository ); précédent : 010577; suivant : 010579Band-gap energies, free carrier effects, and phonon modes in strained GaNAs/GaAs and GaNAs/InAs/GaAs superlattice heterostructures measured by spectroscopic ellipsometry
Auteurs : RBID : Pascal:01-0018943Descripteurs français
- Pascal (Inist)
- 7866F, 7855C, 7830F, 6865C, 7321C, Etude expérimentale, Gallium composé, Gallium arséniure, Semiconducteur III-V, Indium composé, Superréseau semiconducteur, Photoluminescence, Déplacement vers le rouge, Spectre IR, Indice réfraction, Bande interdite, Phonon interface, Fonction diélectrique, TEM, Diffraction RX.
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Abstract
Spectroscopic ellipsometry (SE) is employed to study the optical properties of compressively strained short-period GaAs/InAs/GaNxAs1-x (0%-1 (IR-SE). The undoped SL structures were grown on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). The InAs sequences consist of single monolayers. Structure, composition, layer thicknesses, and parallel and perpendicular lattice mismatch of the samples are studied by high-resolution transmission electron microscopy and high-resolution x-ray diffraction investigations. We employ Adachis critical-point composite model for data analysis in the near-band-gap spectral region (NIR-SE). For analysis of the IR-SE data we use the harmonic oscillator dielectric function model and the Drude model for free-carrier response. We report the direct band-gap energy E0, and the complex index of refraction N=n+ik of the (InAs)/GaNxAs1-x sublayers. We observe the well-known strong redshift of E0 with increase in x, and the strong decrease of the E0 transition amplitude. The E0 values obtained for the SL structures are in good agreement with photoluminescence results. We observe no influence of the InAs monolayer on the spectral position of the fundamental GaNxAs1-x band-to-band transition E0. We detect the transverse-optic (TO) lattice resonance mode of the GaN sublattice at 470 cm-1 within the (InAs)/GaNxAs1-x SL sublayers. The polar strength of the GaN TO mode increases linearly with x. The same techniques were used previously to study tensile strained GaAs/GaNxAs1-x (0%0 [Appl. Phys. Lett. 76, 2859 (2000)], and the amplitude of the GaN TO modes [MRS Internet J. Nitride Semicond. Res. 5, 3 (2000)] on the nitrogen concentration x for tensile strained GaAs/GaNxAs1-x SLs are compared to the results for compressively strained GaAs/InAs/GaNxAs1-x SLs obtained here. We find similar redshift and bowing parameters for E0, but different slopes for the amplitudes of the GaN TO mode. The different slopes are due to the different strain states. From there we calculate the strength of the GaN TO amplitude versus x for strain-compensated InAs/GaNxAs1-x SLs, and the GaN TO mode amplitude can be used to monitor strain or concentration. We further obtain that the InAs monolayer effectively suppresses the effects of free carriers in the GaNxAs1-x sublayers. Absorption by free carriers was observed previously within the tensile strained GaNxAs1-x/GaAs SL heterostructures. This can be explained by the predicted electronic properties of the InAs monolayer, which can effectively bind free holes and free electrons due to folding of the InAs bands along the growth direction [R. C. Iotti, L. C. Andreani, and M. Di Ventra, Phys. Rev. B 57, R15072 (1998)]. The improvement of the morphology of InAs/GaNxAs1-x sublayers is reflected by the decrease of all broadening parameters within both NIR and IR dielectric function models used here, as well as by the occurrence of room-temperature photoluminescence emission. We also discuss IR resonance features due to transverse-magnetic interface modes observed between the Te-doped GaAs and the undoped GaAs buffer layer. We find that these TM interface modes are extremely sensitive to the existence of free carriers within the SL structures. © 2001 American Institute of Physics.
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<record><TEI><teiHeader><fileDesc><titleStmt><title xml:lang="en" level="a">Band-gap energies, free carrier effects, and phonon modes in strained GaNAs/GaAs and GaNAs/InAs/GaAs superlattice heterostructures measured by spectroscopic ellipsometry</title><author><name sortKey="Sik, J" uniqKey="Sik J">J. Sik</name><affiliation wicri:level="2"><inist:fA14 i1="01"><s1>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>5 aut.</sZ></inist:fA14><country xml:lang="fr">États-Unis</country><placeName><region type="state">Nebraska</region></placeName><wicri:cityArea>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln</wicri:cityArea></affiliation><affiliation wicri:level="3"><inist:fA14 i1="03"><s1>Institut fur Oberflachenmodifizierung Leipzig e.V., Permoserstrasse 15, 04303 Leipzig, Germany</s1></inist:fA14><country xml:lang="fr">Allemagne</country><wicri:regionArea>Institut fur Oberflachenmodifizierung Leipzig e.V., Permoserstrasse 15, 04303 Leipzig</wicri:regionArea><placeName><region type="land" nuts="1">Saxe (Land)</region><region type="district" nuts="2">District de Leipzig</region><settlement type="city">Leipzig</settlement></placeName></affiliation></author><author><name sortKey="Schubert, M" uniqKey="Schubert M">M. Schubert</name><affiliation wicri:level="2"><inist:fA14 i1="01"><s1>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>5 aut.</sZ></inist:fA14><country xml:lang="fr">États-Unis</country><placeName><region type="state">Nebraska</region></placeName><wicri:cityArea>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln</wicri:cityArea></affiliation></author><author><name sortKey="Leibiger, G" uniqKey="Leibiger G">G. Leibiger</name><affiliation wicri:level="3"><inist:fA14 i1="02"><s1>Faculty of Chemistry and Mineralogy, University Leipzig, D-04103 Leipzig, Germany</s1><sZ>3 aut.</sZ><sZ>4 aut.</sZ></inist:fA14><country xml:lang="fr">Allemagne</country><wicri:regionArea>Faculty of Chemistry and Mineralogy, University Leipzig, D-04103 Leipzig</wicri:regionArea><placeName><region type="land" nuts="1">Saxe (Land)</region><region type="district" nuts="2">District de Leipzig</region><settlement type="city">Leipzig</settlement></placeName></affiliation></author><author><name sortKey="Gottschalch, V" uniqKey="Gottschalch V">V. Gottschalch</name><affiliation wicri:level="3"><inist:fA14 i1="02"><s1>Faculty of Chemistry and Mineralogy, University Leipzig, D-04103 Leipzig, Germany</s1><sZ>3 aut.</sZ><sZ>4 aut.</sZ></inist:fA14><country xml:lang="fr">Allemagne</country><wicri:regionArea>Faculty of Chemistry and Mineralogy, University Leipzig, D-04103 Leipzig</wicri:regionArea><placeName><region type="land" nuts="1">Saxe (Land)</region><region type="district" nuts="2">District de Leipzig</region><settlement type="city">Leipzig</settlement></placeName></affiliation></author><author><name sortKey="Wagner, G" uniqKey="Wagner G">G. Wagner</name><affiliation wicri:level="2"><inist:fA14 i1="01"><s1>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588</s1><sZ>1 aut.</sZ><sZ>2 aut.</sZ><sZ>5 aut.</sZ></inist:fA14><country xml:lang="fr">États-Unis</country><placeName><region type="state">Nebraska</region></placeName><wicri:cityArea>Center for Microelectronic and Optical Materials Research, and Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln</wicri:cityArea></affiliation></author></titleStmt><publicationStmt><idno type="inist">01-0018943</idno><date when="2001-01-01">2001-01-01</date><idno type="stanalyst">PASCAL 01-0018943 AIP</idno><idno type="RBID">Pascal:01-0018943</idno><idno type="wicri:Area/Main/Corpus">011F74</idno><idno type="wicri:Area/Main/Repository">010578</idno></publicationStmt><seriesStmt><idno type="ISSN">0021-8979</idno><title level="j" type="abbreviated">J. appl. phys.</title><title level="j" type="main">Journal of applied physics</title></seriesStmt></fileDesc><profileDesc><textClass><keywords scheme="KwdEn" xml:lang="en"><term>Dielectric function</term><term>Energy gap</term><term>Experimental study</term><term>Gallium arsenides</term><term>Gallium compounds</term><term>III-V semiconductors</term><term>Indium compounds</term><term>Infrared spectra</term><term>Interface phonons</term><term>Photoluminescence</term><term>Red shift</term><term>Refractive index</term><term>Semiconductor superlattices</term><term>TEM</term><term>XRD</term></keywords><keywords scheme="Pascal" xml:lang="fr"><term>7866F</term><term>7855C</term><term>7830F</term><term>6865C</term><term>7321C</term><term>Etude expérimentale</term><term>Gallium composé</term><term>Gallium arséniure</term><term>Semiconducteur III-V</term><term>Indium composé</term><term>Superréseau semiconducteur</term><term>Photoluminescence</term><term>Déplacement vers le rouge</term><term>Spectre IR</term><term>Indice réfraction</term><term>Bande interdite</term><term>Phonon interface</term><term>Fonction diélectrique</term><term>TEM</term><term>Diffraction RX</term></keywords></textClass></profileDesc></teiHeader><front><div type="abstract" xml:lang="en">Spectroscopic ellipsometry (SE) is employed to study the optical properties of compressively strained short-period GaAs/InAs/GaN<sub>x</sub>As<sub>1-x</sub> (0%<sup>-1</sup> (IR-SE). The undoped SL structures were grown on top of undoped GaAs buffer layers deposited on Te-doped (001) GaAs substrates by metalorganic vapor phase epitaxy (MOVPE). The InAs sequences consist of single monolayers. Structure, composition, layer thicknesses, and parallel and perpendicular lattice mismatch of the samples are studied by high-resolution transmission electron microscopy and high-resolution x-ray diffraction investigations. We employ Adachis critical-point composite model for data analysis in the near-band-gap spectral region (NIR-SE). For analysis of the IR-SE data we use the harmonic oscillator dielectric function model and the Drude model for free-carrier response. We report the direct band-gap energy E<sub>0</sub>, and the complex index of refraction N=n+ik of the (InAs)/GaN<sub>x</sub>As<sub>1-x</sub> sublayers. We observe the well-known strong redshift of E<sub>0</sub> with increase in x, and the strong decrease of the E<sub>0</sub> transition amplitude. The E<sub>0</sub> values obtained for the SL structures are in good agreement with photoluminescence results. We observe no influence of the InAs monolayer on the spectral position of the fundamental GaN<sub>x</sub>As<sub>1-x</sub> band-to-band transition E<sub>0</sub>. We detect the transverse-optic (TO) lattice resonance mode of the GaN sublattice at 470 cm<sup>-1</sup> within the (InAs)/GaN<sub>x</sub>As<sub>1-x</sub> SL sublayers. The polar strength of the GaN TO mode increases linearly with x. The same techniques were used previously to study tensile strained GaAs/GaN<sub>x</sub>As<sub>1-x</sub> (0%<sub>0</sub> [Appl. Phys. Lett. 76, 2859 (2000)], and the amplitude of the GaN TO modes [MRS Internet J. Nitride Semicond. Res. 5, 3 (2000)] on the nitrogen concentration x for tensile strained GaAs/GaN<sub>x</sub>As<sub>1-x</sub> SLs are compared to the results for compressively strained GaAs/InAs/GaN<sub>x</sub>As<sub>1-x</sub> SLs obtained here. We find similar redshift and bowing parameters for E<sub>0</sub>, but different slopes for the amplitudes of the GaN TO mode. The different slopes are due to the different strain states. From there we calculate the strength of the GaN TO amplitude versus x for strain-compensated InAs/GaN<sub>x</sub>As<sub>1-x</sub> SLs, and the GaN TO mode amplitude can be used to monitor strain or concentration. We further obtain that the InAs monolayer effectively suppresses the effects of free carriers in the GaN<sub>x</sub>As<sub>1-x</sub> sublayers. Absorption by free carriers was observed previously within the tensile strained GaN<sub>x</sub>As<sub>1-x</sub>/GaAs SL heterostructures. This can be explained by the predicted electronic properties of the InAs monolayer, which can effectively bind free holes and free electrons due to folding of the InAs bands along the growth direction [R. C. Iotti, L. C. Andreani, and M. Di Ventra, Phys. Rev. B 57, R15072 (1998)]. The improvement of the morphology of InAs/GaN<sub>x</sub>As<sub>1-x</sub> sublayers is reflected by the decrease of all broadening parameters within both NIR and IR dielectric function models used here, as well as by the occurrence of room-temperature photoluminescence emission. We also discuss IR resonance features due to transverse-magnetic interface modes observed between the Te-doped GaAs and the undoped GaAs buffer layer. We find that these TM interface modes are extremely sensitive to the existence of free carriers within the SL structures. © 2001 American Institute of Physics.</div></front>
