Berreman Effect Research Articles

Microstructural and infrared optical properties of electrochemically etched highly doped 4H–SiC

Pores in porous 4H–SiC are found to propagate first nearly parallel with the basal plane and then gradually change plane of propagation towards the direction of the c axis. A similar anisotropy in pore propagation is found in porous 6H–SiC. A disordered phase is encountered at the interface between crystalline SiC and the pores. Formation of this phase was attributed to the etching conditions. Characterization of the material with nondestructive infrared spectroscopic ellipsometry in the photon energy range 0.062–0.62 eV provides average thickness and porosity in good agreement with electron microscopy observations. Anodization of SiC introduces remarkable changes to the reststrahlen band. A shallow minimum at 0.113 eV is attributed to the Berreman effect. In addition, a sharp peak at 0.126 eV is discussed to be related to the in-depth inhomogeneity and particle shape effects in the material.

In situ Fourier transform P-polarized infrared reflection absorption spectroscopic investigation of an interface properties of SiO 2/Si(100) deposited using electron cyclotron resonance microwave plasma at room temperature

Amorphous SiO 2 films have been deposited onto the Si substrate, without heating, using sputtering-type electron cyclotron resonance (ECR) microwave plasma. In situ Fourier transform P-polarized infrared reflection absorption spectroscopy (ISFT-PIRRAS) has been used to study the properties of a-SiO 2/Si interface. The results from ISFT-PIRRAS monitoring indicated that the interface stress led to significant distortion in the local structure, which resulted in the broadening of a transverse optical mode (TO 3) located at 1050 cm −1. The interface stress decreased with increased film thickness. In addition, the longitudinal optical phonon mode (LO 3, located at 1223 cm −1) related to TO 3 mode was observed due to Berreman effect [B. Harbecke, Appl. Phys. A: Solids Surf. 38 (1985) 263]. This phonon mode is very sensitive to SiO 2 film thickness, which enables it to be used to detect and characterize ultra thin SiO 2 film. When the film thickness is over 30 nm, a non-linear dependence of the intensity of LO 3 mode on film thickness was observed. However, the TO 3 mode has a near linear dependence on film thickness. Thus, it is more accurate and suitable to detect thick film by monitoring TO 3 mode intensity.

Observation of the Berreman Effect in Infrared Reflection-Absorption Spectra of Amorphous Titanium Oxide Thin Films Deposited on Aluminum

Infrared reflection-absorption spectra of plasma-enhanced chemical vapor deposition (PECVD) amorphous TiO2 thin films on aluminum were obtained with s- and p-polarized light and oblique incidence angles. Such spectra were analyzed by means of spectral simulations based on a Fresnel equation for a three-layered system. The optical constants used in the simulations were obtained through the Kramers–Krönig analysis of the reflectance spectra of a pellet of powdered amorphous TiO2. LO-TO energy-loss functions were also calculated from these optical constants, and a splitting was observed. A good qualitative agreement between experimental and simulated spectra was achieved, and the Berreman effect was observed in both cases when p-polarized light was used. It was shown, therefore, that the Berreman effect makes infrared reflection-absorption spectroscopy a successful technique for the characterization of an amorphous TiO2 thin layer on aluminum.

Carrier concentration and lattice absorption in bulk and epitaxial silicon carbide determined using infrared ellipsometry

We have measured the dielectric function of bulk nitrogen-doped 4H and 6H SiC substrates from 700 to 4000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ using Fourier-transform infrared spectroscopic ellipsometry. Photon absorption by transverse optical phonons produces a strong reststrahlen band between 797 and 1000 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ with the effects of phonon anisotropy being observed in the region of the longitudinal phonon energy (960 to 100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$). The shape of this band is influenced by plasma oscillations of free electrons, which we describe with a classical Drude equation. For the 6H-SiC samples, we modify the Drude equation to account for the strong effective mass anisotropy. Detailed numerical regression analysis yields the free-electron concentrations, which range from $7\ifmmode\times\else\texttimes\fi{}{10}^{17}$ to ${10}^{19}{\mathrm{cm}}^{\mathrm{\ensuremath{-}}3},$ in good agreement with electrical and secondary ion mass spectrometry measurements. Finally, we observe the Berreman effect near the longitudinal optical phonon energy in $n\ensuremath{-}/n+$ homoepitaxial 4H SiC and hydrogen implanted samples, and we are able to determine the thickness of these surface layers.

The Origin of the Berreman Effect in SiC Homostructures

physica status solidi (b)Volume 208, Issue 1 p. R3-R4 Rapid Research Note The Origin of the Berreman Effect in SiC Homostructures St. Zollner, St. Zollner Motorola SPS, MD M360, 2200 West Broadway Rd, Mesa AZ 85202, USA, Phone: 602 655 4655, FAX: 602 655 5013Search for more papers by this authorJ. P. Carrejo, J. P. Carrejo Motorola SPS, MD M360, 2200 West Broadway Rd, Mesa AZ 85202, USA, Phone: 602 655 4655, FAX: 602 655 5013Search for more papers by this authorT. E. Tiwald, T. E. Tiwald Department of Electrical Engineering, University of Nebraska, Lincoln NE 68588-0511, USASearch for more papers by this authorJ. A. Woollam, J. A. Woollam Department of Electrical Engineering, University of Nebraska, Lincoln NE 68588-0511, USASearch for more papers by this author St. Zollner, St. Zollner Motorola SPS, MD M360, 2200 West Broadway Rd, Mesa AZ 85202, USA, Phone: 602 655 4655, FAX: 602 655 5013Search for more papers by this authorJ. P. Carrejo, J. P. Carrejo Motorola SPS, MD M360, 2200 West Broadway Rd, Mesa AZ 85202, USA, Phone: 602 655 4655, FAX: 602 655 5013Search for more papers by this authorT. E. Tiwald, T. E. Tiwald Department of Electrical Engineering, University of Nebraska, Lincoln NE 68588-0511, USASearch for more papers by this authorJ. A. Woollam, J. A. Woollam Department of Electrical Engineering, University of Nebraska, Lincoln NE 68588-0511, USASearch for more papers by this author First published: 29 January 1999 https://doi.org/10.1002/(SICI)1521-3951(199807)208:1<R3::AID-PSSB99993>3.0.CO;2-XCitations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article.Citing Literature Volume208, Issue1July 1998Pages R3-R4 RelatedInformation

Infrared Reflection Absorption Spectroscopy of Naturally Grown Oxide Films on Chrome and the Dependence of the Berreman Effect on Film Thickness

The thickness dependence of the Berreman effect for naturally grown oxide films on chrome is analyzed theoretically and experimentally. The shift of the spectral position of the Berreman minimum can be described by the Fuchs–Kliewer theory of virtual modes. Both the absorption and the shift of the position can be used for thickness determination. The experimental results compared with calculated values based on different optical constants for Cr2O3 indicate their influence on the position and the absorption of the Berreeman minimum.

Determination of Thickness of Thin Thermal Oxide Layers on Czochralski-Grown Silicon Wafers from their Longitudinal Optical Vibrational Mode

Infrared transmission spectra of the longitudinal optical (LO) mode (1250 cm-1) of thin thermal oxide layers (10–100 Å, formed at 800–950° C in O2 or O2 diluted with N2) on silicon wafers were measured at p-polarized 73.7° incidence, based on the Berreman effect. An excellent linear correlation was found between the LO absorbance and the oxide thickness, which exhibits no dependence upon the oxygen content in silicon.

Infrared reflectance studies on a Fe3O4 film deposited on a MgO substrate: Observation of the substrate longitudinal optic phonon resonance peak in the film geometry.

Infrared reflectance spectra were measured on a ${\mathrm{Fe}}_{3}$${\mathrm{O}}_{4}$ film deposited on a bulk MgO substrate. For an obliquely incoming light with TM polarization, the reflectance spectra showed a peak structure near a longitudinal optic (LO) phonon frequency of MgO. For TE polarization, such a resonant structure was not observed. This phenomenon is quite different from the ``Berreman effect'' [D. W. Berreman, Phys. Rev. 130, 2193 (1963)], where an absorption process related to a LO phonon of the film occurs instead of that of the substrate. For our film geometry, the electric field component normal to the film induces charge oscillations and a coupling between the charge carriers in the film and the LO phonon of MgO results in the resonance phenomenon. The resonance peak occurs at a frequency where the substrate dielectric constant becomes the same as ${\mathrm{sin}}^{2}$${\mathrm{\ensuremath{\theta}}}_{0}$, where ${\mathrm{\ensuremath{\theta}}}_{0}$ is the incident angle. This newly observed phenomenon might be useful to investigate a LO phonon of a solid, where other methods are difficult to be applied. \textcopyright{} 1996 The American Physical Society.

Infrared observation of transverse and longitudinal polar optical modes of semiconductor films: Normal and oblique incidence.

The observation of the zone-center transverse optic (TO) and longitudinal optic (LO) phonons of a polar semiconductor crystal as transmission minima in its infrared spectrum, when measured with radiation obliquely incident on a thin film of the crystal, i.e., the Berreman effect, is applied to a diverse group of II-VI and III-V epilayers and superlattices grown by molecular-beam epitaxy (MBE) as well as epilayers of SiC on a Si substrate and free-standing CdS films grown by chemical-vapor deposition (CVD). Whereas the TO phonon appears irrespective of the polarization of the incident radiation for both normal and oblique incidence, the LO phonon can be detected only in the latter with light polarized in the plane of incidence. The technique, successfully applied to tetrahedrally coordinated zinc-blende MnTe, accessible only with MBE growth on GaAs, has resulted in a direct observation of its TO and LO modes. Zinc-blende ${\mathrm{Cd}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Se grown on GaAs by MBE, similarly investigated, yields the frequencies of the CdSe-like and MnSe-like TO and LO modes as a function of x, including those for cubic CdSe (x=0) and, by extrapolation to x=1, for zinc-blende MnSe. In the II-VI/II-VI superlattices, confinement of the optical phonons has been observed. In free-standing CdS films with the wurtzite structure, their optic axis being in the plane of the film, the ${\mathit{A}}_{1}$(TO), ${\mathit{E}}_{1}$(TO), and ${\mathit{E}}_{1}$(LO) zone-center phonons have been directly observed. In a GaAs/AlAs/GaAs structure grown by MBE, the LO and TO modes of the submicrometer AlAs epilayer and the GaAs cap layer were observed with the Berreman technique, before and after removing the GaAs substrate, respectively. Finally, the Berreman effect of cubic SiC, grown on a Si substrate by CVD, illustrates the power of the technique in the context of a material of increasing technological importance.

Infrared observation of longitudinal optical modes in MBE-grown polar semiconductors films

The feasibility of observing the zone-center longitudinal optical phonon (LO) of a crystal as a minimum in its infrared transmission spectrum, when measured with radiation obliquely incident on a thin film of the crystal, i.e., the Berreman effect, is demonstrated with an MBE′-grown zinc-blende MnTe epilayer. Whereas the zone-center transverse optic phonon (TO) appears irrespective of the polarization of the incident radiation for both normal and oblique incidence, the LO can be detected only in the latter with light polarized in the plane of incidence. We have verified the Berreman effect in a variety of MBE-grown II–VI epilayers and heterostructures.

IR spectroscopic ellipsometry: instrumentation and results

For photometric IR ellipsometry the principles of operation are outlined. The experimental procedure, being based on Fourier transform spectrometry, and other particulars of this spectral range as to the physical effects and the optical components are discussed. By ellipsometry the complete determination of the optical properties of the samples whether solids, pressed powders, liquids, or others is achieved; it is shown that this widens the scope of IR spectroscopy in comparison with traditional techniques and grants an extended, detailed description of surface phenomena related for example to surface polaritons, wave guides, or the Berreman effect. Illustrative results from some typical applications are given.

Characterization of radiative surface modes and anisotropy in Ag/SiO2 multilayers, by visible and IR ellipsometry

Ellipsometric measurements in the visible (1.4–5.4 eV) and the IR (0.03–0.5 eV) have been performed on metal/dielectric (Ag/SiO2) periodic multilayers prepared by magnetron sputtering. The results are discussed in terms of radiative modes occuring at the plasma frequency of the metal (3.78 eV) and the longitudinal optical (0.154 eV) and transverse optical (0.133 eV) frequencies of the dielectric. A strong anisotropy is observed near these resonances. It is shown to be due to coupling effects in the multilayer in the visible range and to a classical Berreman effect in the first dielectric layer in the IR range. These effects have potential applications to optical coatings for the IR and for optical communications.

Infrared absorption in SiO2-Ge composite films: Influences of Ge microcrystals on the longitudinal-optical phonons in SiO2.

Infrared absorption in composite films of ${\mathrm{SiO}}_{2}$ and microcrystalline Ge has been investigated with p- and s-polarized light under 45\ifmmode^\circ\else\textdegree\fi{} oblique incidence. In the case of p-polarized incident light, pure ${\mathrm{SiO}}_{2}$ films clearly exhibit an absorption peak of the LO-phonon mode around 1240 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in addition to that of the TO mode at 1080 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, due to the so-called Berreman effect. It was found that the intensity of the LO absorption relative to that of the TO absorption decreases as the volume fraction of Ge microcrystals in the film increases. Theoretical calculations based on the Bruggeman and Maxwell-Garnett effective-medium theories have been performed. The calculations made by the Bruggeman theory could successfully reproduce the observed spectra and well explain the decrease in the intensity of the LO absorption, while those made by the Maxwell-Garnett theory disagreed with the experiments.

Problem of polarization degree in spectroscopic photometric ellipsometry (polarimetry)

The significance of the degree of polarization on reflection from the sample in photometric ellipsometry is examined. The degree of polarization was calculated from the four Stokes parameters that were measured by photometric ellipsometry in the IR region, including an additional retarder in the experimental setup. Examples are given for the polarization-degree spectra in the IR region for film-covered surfaces and polished surfaces as well as for the excitation of surface polaritons and the Berreman effect [ Phys. Rev.130, 2193 ( 1963)]. In some cases the polarization effects can be explained by an averaging process of the ellipsometric phase over the investigated region.

Optical properties of thin films and the Berreman effect

The measurement of reflection and transmission of normally incident light to obtain the optical constants of a material is a usual tool in solid-state spectroscopy. If the material under investigation is a thin film, the interaction of the electromagnetic field with the sample can be enhanced by oblique incidence. If the light is p-polarized, structures in the reflection and transmission spectra are observed at the frequencies of transverse (TO) and longitudinal (LO) resonances. The LO structure — called the Berreman effect — is generated by the surface charges due to the normal component of the electric field. We discuss this effect for three cases: a free film, a film with a metallic back and a substrate with thin films on both sides. The dependence of the effect on the energy-loss function Im {−1/ɛ} and on the film thickness is discussed. For idealized systems simple formulae are derived and a characteristic parameter, called the Berreman thickness, is obtained. Films of this thickness show a maximum effect. Intuitive arguments are given to explain the effect. Examples for the application of the Berreman effect to characterize very thin films are discussed.