Chromatic interferometry for an intelligent plasma processing system

The thermal conductivities of thin crystalline semiconductor films in novel electrical and optical devices can differ from bulk values due to the size effect on lattice thermal conductivity, which is caused by phonon-boundary scattering. For many semiconductors at or above room temperature, the size effect is strongly influenced by the highly dispersive nature of their phonon spectra and the varying contribution of each phonon branch to heat conduction. The present study reviews existing thermal conductivity models for bulk semiconductor samples and examines the impact of the phonon dispersion on the size effect. Based on the observed strong dependence of the size effect on the phonon branch contributions, we demonstrate that the investigation of thin-film thermal conductivity at high temperatures can help the theoretical understanding of lattice thermal conduction. For silicon thin films studied here better agreement between the predicted in-plane thermal conductivity and the existing experimental data is achieved by assuming that longitudinal phonons are the dominant heat carriers. The practically-relevant problem of phonon scattering at the interface between crystalline silicon and amorphous silicon dioxide layers is discussed.

Summary form only given. In this talk we present a self-consistent model for calculating the lattice thermal conductivity in semiconductor thin films and nanowires. The model is based on the solution of the phonon Boltzmann equation. It rigorously takes into account modification of the acoustic phonon dispersion in low-dimensional structures with the lateral feature size of 10 nm - 30 nm, and change in the non-equilibrium phonon distribution due to partially diffuse scattering from rough boundaries and interfaces. It is shown that the presence, of distinctive boundaries in such structures leads to a transformation of the acoustic branches of phonon dispersion to quasi-optical branches characterized by a low group velocity and different cut-off frequencies. This transformation affects both in-plane and cross-plane thermal conduction in low-dimensional structures. In this talk we also analyze three-phonon Umklapp scattering processes in thin films and nanowires and compare them with those in bulk semiconductors. The predictions. of the thermal conductivity. values based on our model are in good agreement with available experimental data for silicon thin films and nanowires. The described changes in phonon transport in semiconductor thin films and nanowires bear important consequences for nanostructure and device simulation since neither Fourier beat theory nor Debye approximation are accurate at nanometer length scale. The observed modification of the thermal resistance of the low-dimensional structures has to be taken into account in simulation of thermal transport in deep-submicron devices since, it strongly affects the electrostatic, discharge voltage (EDS) and other reliability characteristics. The change in the acoustic phonon dispersion and group velocity may be partially responsible for the experimentally observed drop of EDS in devices based on thin-film silicon-on-insulator (SOI) wafers.

A user-friendly software PRISA has been developed to determine optical constants (refractive index and extinction co-efficient), dispersion parameters (oscillator energy and dispersion energy), absorption co-efficient, band gap and thickness of semiconductor and dielectric thin films from measured transmission spectrum, only. The thickness, refractive index, and extinction co-efficient of the films have been derived using Envelope method proposed by Swanepoel. The absorption co-efficient in the strong absorption region is calculated using the method proposed by Connel and Lewis. Subsequently, both direct and indirect bandgap of the films is estimated from the absorption co-efficient spectrum using Tauc plot. The software codes are written in Python and the graphical user interface is programmed with tkinter package of Python. It provides convenient input and output of the measured and derived data. The software has a feature to cross check the results by retrieving transmission spectrum using the values of refractive index, extinction co-efficient, and thickness obtained from Envelope method. The performance of the software is verified by analyzing numerically generated transmission spectra of a-Si:H amorphous semiconductor thin films, and experimentally measured transmission spectra of electron beam evaporated HfO2 dielectric thin films as examples. PRISA is found to be much simpler and accurate as compared to the other freely available softwares. To help researchers working on thin films, the software is made freely available at https://www.shuvendujena.tk/download.

Femtosecond-laser induced two-photon absorption of GaN and AlxGa1-xN thin films: Tuning the nonlinear optical response by alloying and doping

We study theoretically the effect of acoustic-phonon confinement on the phonon-drag thermopower ${S}^{g}$ of a two-dimensional (2D) electron gas in a quantum well embedded in a semiconductor thin film. The screened interaction of 2D electrons via the deformation and piezoelectric potentials in the film with stress-free surfaces is considered. Analytical expressions are obtained for ${S}^{g}$ (due to flexural, dilational, and shear modes) in the Bloch-Gruneisen regime where the nature of confinement is pronounced. Interestingly, ${S}^{g}$ dependence on temperature $T$ is the same for both deformation and piezoelectric potential mechanisms, which may be attributed to the similar phonon wave vector dependence of their interaction matrix elements at very low temperatures. We find ${S}^{g}\ensuremath{\sim}{T}^{3}$ for flexural modes and ${T}^{5}$ for dilatational and shear modes. ${S}^{g}$ due to flexural modes, which have quadratic dispersion and high density of states, is found to be dominant over contribution from other modes. ${S}^{g}$ in thin films is suppressed due to a smaller phonon mean free path compared to bulk phonons. Herring's formula relating ${S}^{g}$ to phonon limited mobility ${\ensuremath{\mu}}_{p}$ is discussed. We find ${S}^{g}{\ensuremath{\mu}}_{p}\ensuremath{\sim}{T}^{\ensuremath{-}1/2}$ for flexural modes and ${T}^{\ensuremath{-}1}$ for dilatational and shear modes showing the invalidity of the Herring's formula for flexural modes.

Chapter 6 - Protecting Critical Infrastructure: Process Control and SCADA

This paper presents the results of investigating the parameters (minimum repetition period of the elements and porosity) of structures obtained under the action of argon laser radiation on thin films of glassy chalcogenide semiconductor deposited on layers of x-ray-amorphous chromium. It is shown that thin films of a three-component glassy semiconductor exposed by radiation with wavelength 0.488 µm can be used in the method of interference photolithography to obtain structures with a minimum period of 260 nm and a minimum size of the structural element of 65 nm. It is established that the minimum size of a structural element can be reduced to 50 nm when the repetition period of the elements is increased to 600 nm by using the “two-mask” technology of interference photolithography.

We study wave propagation in a piezoelectric ceramic half-space with a thin semiconductor film and an air gap between the film and the half-space. Two-dimensional equations for a thin film are used to model the semiconductor film and the air gap. The half-space is governed by the three-dimensional equations of linear piezoelectricity. It is shown that an anti-plane wave can propagate in such a system. An equation that determines the dispersion relation of the wave is obtained. Solutions to the equation show that the wave has both dispersion and attenuation, and can be amplified by a biasing dc electric field.

The structure study of thin semiconductor and dielectric films by diffraction of synchrotron radiation

Structure and properties of amorphous thin film for optical data storage

Thin films of AlN, CrN and Al1-xCrxN were grown epitaxially on c-cut sapphire by radio frequency (RF) plasma assisted pulsed laser deposition (PLD). The PLD growth mode employed for these Al1-xCrxN films was by delta doping layers of CrN 0.05-0.10 nm thick between layers of AlN of approximately 3.6 nm thick giving an estimated 1.3% and 2.5% Cr doping. The substrate temperature, nitrogen pressure and power parameters of the RF plasma were varied to optimize crystalline growth. X-ray diffraction (XRD) confirmed hexagonal wurtzite thin film growth of highly crystalline AlN and highly crystalline cubic CrN. The electronic structure of these thin films was examined by x-ray absorption (XAS) and soft x-ray emission spectroscopy (XES) at the N K edge. These measurements are compared with the results of density functional calculations for wurtzite-AlN, cubic-CrN and wurtzite-Al1-xCrxN. [DOI: 10.1380/ejssnt.2009.497]

High performance piezoelectric thin films are generally lead-based, and find applications in sensing, actuation and transduction in the realms of biology, nanometrology, acoustics and energy harvesting. Potassium sodium niobate (KNN) is considered to be the most promising lead-free alternative, but it is hindered by the inability to control and attain perfect stoichiometry materials in the thin film form while using practical large area deposition techniques. In this work, we identify the contribution of the elemental diffusivities in the radio frequency (RF) plasma in determining the alkali loss in the KNN thin films. We have also examined the effect of the substrate temperature during the RF magnetron sputtering deposition on the crystal structure of the substrate and KNN thin films, as well as the effect of the post-annealing treatments. These results indicate the need for well-designed source materials and the potential to use the deposition partial pressure to alter the dopant concentrations.

Epitaxial growth of phase-pure and high-quality spinel γ-Ga2O3-based semiconductor thin films has been a big challenge for fundamental research on metastable defective inverse spinel γ-Ga2O3 semiconductors in view of potential device application. We report experimental results on epitaxial growth, microstructural, and electrical transport properties of (001)-oriented nominal γ-(Ga0.8Ge0.2)2O3 alloy semiconductor single crystal thin films with a coherent interface on cubic spinel (001) MgAl2O4 substrates by pulsed laser deposition using a Ge-rich target. Pristine films are found to be composed of about 2 nm thick insulating Ge-rich surface layers and the high-quality epitaxial n-type semiconductor film layers consisting of partially subvalent Ge2+ and Ga1+ cations as well as major components of normal Ge4+ and Ga3+ cations. Epitaxial films exhibit a direct bandgap of about 5.2 ± 0.1 eV and a valence band maximum of about 3.3 ± 0.1 eV below the Fermi level at room temperature. We further report a demonstration of γ-(Ga0.8Ge0.2)2O3 thin film-based metal-semiconductor field-effect transistor (MESFET) with the PtOx/Pt Schottky gate contact realized upon the surface pretreatment by Ar/O2 plasma etching. The MESFET device exhibits a clear field-effect with drain current modulation of about 105 orders of magnitude. This work not only significantly advances the fundamental and application-oriented research on epitaxial spinel γ-Ga2O3-based semiconductor films for practical device application but also offers new insight into microstructural characteristics of ultrawide bandgap spinel oxide semiconductor epitaxial thin films.

Recently, several techniques have been developed to simultaneously examine species formed during electrochemical reactions. For exmaple, in situ spectroscopic−electrochemical methods yield data to characterize electrode processes and possibly elucidate electrocatalytic reactions. Spectroelectrochemistry utilizes optically transparent electrodes (OTE) to measure with transmission, internal reflectance, or reflection spectroscopy the rates of formation and disappearance of electrogenerated species. These OTE’s are either metal or semiconductor thin films which are chemically inert and have optical properties compatible with the experiment. Optical data gives a clearer picture of the electrochemistry at the solution/electrode interface. These types of electrochemical data may also be used to characterize surfaces of the thin film electrodes. Application of thin deposited films to spectroelectrochemical studies are reviewed. Simultaneous spectroscopic and voltametric results are shown for Pt films deposited u...

Numerical simulations of time-dependent energy transport in semiconductor thin films are conducted by using the Lattice-Boltzmann method applied to phonon transport. The discrete Lattice-Boltzmann method is first derived from the continuous Boltzmann transport equation, where nonlinear phonon dispersion relations are used to find frequency-dependent phonon velocities for longitudinal acoustic phonons. A Silicon-on-Insulator (SOI) transistor is modeled as a thin film of silicon, with a hotspot simulated by imposing a heat generation term in a localized region of the computational domain. Results indicate that a transition from diffusive to ballistic energy transport is found as the characteristic length of the thin film becomes comparable to the phonon mean free path. This transition is present in heat conduction in thin films as well as in the transient thermal response of SOI transistors. Steady-state temperature distributions are then used to calculate size-dependent thermal conductivity values in silicon thin films.