Bulletin of the American Physical Society
Annual Meeting of the APS Four Corners Section
Volume 60, Number 11
Friday–Saturday, October 16–17, 2015; Tempe, Arizona
Session D5: Materials II: Semiconductors and Optical Characterization |
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Chair: Andrew Chizmeshya, Arizona State University Room: MU220 |
Friday, October 16, 2015 1:50PM - 2:02PM |
D5.00001: Strain dependence of the band structure and critical points of pseudomorphic Ge$_{1-y}$Sn$_{y\, }$alloys on Ge Nalin Fernando, Jaime Moya, Stefan Zollner, John Hart, Dainan Zhang, Ryan Hickey, Ramsey Hazbun, James Kolodzey The energy band structure of Ge is a strong function of strain, and a transition from an indirect to a direct band gap has been observed for y \textasciitilde 6-10{\%} for Ge$_{1-y}$Sn$_{y}$ indicating the possibility of widespread applications of Ge-based photonic devices. Hence it is important to study the composition and strain dependence of the Ge$_{1-y}$Sn$_{y}$ alloy band structure through measurements of the optical properties. The complex pseudodielectric functions of pseudomorphic Ge$_{1-y}$Sn$_{y}$ alloys grown on Ge by MBE were measured using spectroscopic ellipsometry and FTIR ellipsometry in the 0.1-6.6 eV energy range for Sn contents up to 10{\%}, to investigate the compositional dependence of the direct band gap E$_{0}$, E$_{1}$~and E$_{1}+\Delta _{1}$~critical point (CP) energies. CP energies and related parameters were obtained by analyzing the second-derivative of the dielectric function. Our experimental results are in good agreement with the theoretically predicted~CP energies of Ge$_{1-y}$Sn$_{y}$ on Ge based on deformation potential theory. We will present the nature of the band gap of pseudomorphic Ge$_{1-y}$Sn$_{y}$ on Ge and the effects of strain that control the indirect to direct band gap transition. [Preview Abstract] |
Friday, October 16, 2015 2:02PM - 2:14PM |
D5.00002: Growth and Properties of Ge Thermal Oxides T. Nathan Nunley, Nalin Fernando, Jaime Moya, Cayla M. Nelson, Stefan Zollner The optical constants of thermal germanium dioxide have been determined in the spectral range of 0.037-6.6 eV using a combination of variable angle VUV and FTIR ellipsometric techniques and X-ray reflectance. Oxides with thicknesses from 2 to 100 nm were prepared by ozone cleaning for 2 hours, performing an ultrasonic clean with DI water and isopropanol for twenty minutes respectively, drying with N$_{2}$ and growing in dry O$_{2}$ at 550 \textdegree C. XRR was performed to obtain an independent thickness measurement and electron density. The optical spectra of all samples were analyzed simultaneously for an independent determination of the optical constants for both substrate and oxide. A single model, consisting of a sum of oscillators for interband electronic transitions and a factorized dispersion model for the phonons, was used. [Preview Abstract] |
Friday, October 16, 2015 2:14PM - 2:26PM |
D5.00003: Rutherford backscattering measurements of Bi mole fraction and site distribution in InAsBi Arvind J. Shalindar, Preston T. Webster, Barry J. Wilkens, Terry L. Alford, Shane R. Johnson Several narrow bandgap InAsBi layers grown by molecular beam epitaxy are structurally examined using Rutherford backscattering spectrometry (RBS) and x-ray diffraction (XRD). The samples are 1 $\mu $m thick, nearly lattice matched to GaSb substrates, and grown at temperatures ranging from 270 to 280 \textdegree C with As/In flux ratios from 0.96 to 1.05 and Bi/In flux ratios from 0.060 to 0.065 [1]. Transmission electron microscopy measurements of these samples indicate excellent crystallinity, no ordering, no visible defects over large lateral distances, and lateral fluctuation of the Bi mole fraction on a 100 nm length scale [2]. Random RBS measurements indicate that the average Bi content of the InAsBi sample set ranges from 5.0{\%} to 6.5{\%} and XRD measurements exhibit sidebands arising from the presence of small regions of InAsBi with lower Bi mole fractions than that specified by the main diffraction peak. RBS ion channeling measurements indicate the presence of approximately 1{\%} interstitial Bi atoms. [1] P. T. Webster, N. A. Riordan, C. Gogineni, S. Liu, J. Lu, X.-H. Zhao, D. J. Smith, Y.-H. Zhang, S. R. Johnson, J. Vac. Sci. Technol., B, 32, 02C120 (2014) [2] J. Lu, P. T. Webster, S. Liu, Y.-H. Zhang, S. R. Johnson, D. J. Smith, J. Cryst. Growth 425, 250 (2015) [Preview Abstract] |
Friday, October 16, 2015 2:26PM - 2:38PM |
D5.00004: Electronic states of plasma-enhanced atomic layer deposited SiO2 on GaN Brianna Eller, Wenwen Li, Sarah Rupprecht, Srabanti Chowdhury, Robert Nemanich Silicon dioxide is a stable dielectric with a large bandgap that leads to effective band offsets suitable for wide bandgap semiconductor electronics. This research is focused on band offsets and bending for plasma-enhanced atomic layer deposited (PEALD) SiO2 on GaN. We have thus investigated SiO2 using tris(dimethylamino)silane (TDMAS) and oxygen plasma on GaN substrates. Film thicknesses, compositions, and band offsets were determined with \textit{in-situ} x-ray photoelectron spectroscopy (XPS). Results showed the growth rate for TDMAS and oxygen plasma process increased as temperature decreased within the ALD regime. The growth rate was higher at 550\textdegree C, which was likely the result of thermal decomposition of TDMAS. Results demonstrated temperature does not greatly affect the stoichiometry of the films. A more detailed analysis showed increasing deposition temperature resulted in a secondary O1s peak; however, this peak was not present for thick films. This secondary peak likely suggests high temperatures relate to the oxidization of the GaN substrates. This effect may also explain the variation in observed valence band offsets (VBO), where the measurement technique does not account for the potential drop across an interfacial Ga-O layer. [Preview Abstract] |
Friday, October 16, 2015 2:38PM - 3:02PM |
D5.00005: How thick is my film? Invited Speaker: Stefan Zollner Modern semiconductor devices for phones or laptops contain 40 or more different layers (insulators, semiconductors, metals). The device response (current versus voltage) and reliability depend critically on the individual layer thicknesses. This makes the art of measuring thicknesses very important. As physicists, we easily understand that thicknesses can be measured very quickly using optical or x-ray interference techniques, if the wavelength of the light is on the order of the film thickness. I will show examples of such thickness measurements from the latest semiconductor technology process flows. I will also describe other physics-based thickness measurement techniques, such as characteristic x-ray emission or x-ray diffraction. The most powerful measurement technique found in every semiconductor factory is spectroscopic ellipsometry, which detects the change in the polarization of light when it is reflected by a layered semiconductor structure. [Preview Abstract] |
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