Ultralow Index SiO 2 Antireflection Coatings Produced via Magnetron Sputtering
Not provided.
Chemistry↗
Engineering topics
Cleri, Angela
Publications and source records attributed to Cleri, Angela.
Effects of strain, disorder, and Coulomb screening on free-carrier mobility in doped cadmium oxide
Here, the interplay of stress, disorder, and Coulomb screening dictating the mobility of doped cadmium oxide (CdO) is examined using Raman spectroscopy to identify the mechanisms driving dopant incorporation and scattering within this emerging infrared optical material. Specifically, multi-wavelength Raman and UV-vis spectroscopies are combined with electrical Hall measurements on a series of yttrium (X = Y) and indium (X = In) doped X:CdO thin-films. Hall measurements confirm n-type doping and establish carrier concentrations and mobilities. Spectral fitting along the low-frequency Raman combination bands, especially the TA+TO(X) mode, reveals that the evolution of strain and disorder within the lattice as a function of dopant concentration is strongly correlated with mobility. Coupling between the electronic and lattice environments was examined through analysis of first- and second-order longitudinal–optical phonon–plasmon coupled modes that monotonically decrease in energy and asymmetrically broaden with increasing dopant concentration. By fitting these trends to an impurity-induced Fröhlich model for the Raman scattering intensity, exciton–phonon and exciton–impurity coupling factors are quantified. These coupling factors indicate a continual decrease in the amount of ionized impurity scattering with increasing dopant concentration and are not as well correlated with mobility. This shows that lattice strain and disorder are the primary determining factors for mobility in donor-doped CdO. In aggregate, the study confirms previously postulated defect equilibrium arguments for dopant incorporation in CdO while at the same time identifying paths for its further refinement.
42 ENGINEERING↗
Lattice Quality Limits Mobility in Donor Doped CdO.
Abstract not provided.
Piontkowski, Zachary Tyler↗
Mid-wave to near-IR optoelectronic properties and epsilon-near-zero behavior in indium-doped cadmium oxide
Indium-doped cadmium oxide (In:CdO) thin films exhibit tunable epsilon-near-zero (ENZ) modal frequencies across a wide spectral range, bridging the mid-wave and near-infrared (IR). In:CdO thin films are prepared by reactive cosputtering from metallic Cd and In targets using high-power impulse magnetron sputtering (HiPIMS) and radio frequency sputtering, respectively. Using this approach, CdO thin films with carrier concentrations ranging from 2.3 × 10 19 to 4.0 × 10 20 cm –3 and mobilities ranging from 300 to 400 cm 2 /Vs are readily achieved. UV-VIS absorption spectra are used to measure optical bandgap, revealing a Burstein-Moss shift of 0.58 eV across the doping range investigated. In this work, optical measurements demonstrate the tunability of near-perfect plasmonic ENZ absorption across the mid-wave and into the near-IR spectral ranges by controlling the carrier concentration through doping, while tuning the film thickness for impedance matching. In comparison to other dopants that can be introduced to HiPIMS-deposited CdO, In offers the largest range of carrier concentrations while maintaining high mobility, thus allowing for the widest accessibility of the IR spectrum of a single plasmonic material grown by sputtering.
36 MATERIALS SCIENCE↗
Ultraviolet to far-infrared dielectric function of n -doped cadmium oxide thin films
Spectroscopic ellipsometry and Fourier transform infrared spectroscopy were applied to extract the ultraviolet to far-infrared (150 – 33333 cm -1 ) complex dielectric functions of high-quality, sputtered indium-doped cadmium oxide (In:CdO) thin crystalline films on MgO substrates possessing carrier densities (N d ) ranging from 1.1 x 10 19 cm -1 to 4.1 x 10 20 cm -1 . A multiple oscillator fit model was used to identify and analyze the three major contributors to the dielectric function and their dependence on doping density: interband transitions in the visible, free-carrier excitations (Drude response) in the near- to far-infrared, and IR-active optic phonons in the far-infrared. More specifically, values pertinent to the complex dielectric function such as the optical band gap (E g ), are shown here to be dependent upon carrier density, increasing from approximately 2.5–3 eV, while the high-frequency permittivity (ε ∞ ) decreases from 5.6 to 5.1 with increasing carrier density. The plasma frequency (ω p ) scales as $\sqrt{N_d}$, resulting in ω p values occurring within the mid- to near-IR, and the effective mass (m *) was also observed to exhibit doping density-dependent changes, reaching a minimum of 0.11 m o in unintentionally doped films (1.1 x 10 19 cm -1 ). Good quantitative agreement with prior work on polycrystalline, higher-doped CdO films is also demonstrated, illustrating the generality of the results. The analysis presented here in this paper will aid in predictive calculations for CdO-based next-generation nanophotonic and optoelectronic devices, while also providing an underlying physical description of the key properties dictating the dielectric response in this atypical semiconductor system.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗