Modified Tauc–Lorentz dispersion model leading to a more accurate representation of absorption features below the bandgap

Phonon-assisted anti-Stokes emission and its stimulated emission in polar semiconductor ZnTe are demonstrated via the annihilation of phonons as a result of strong exciton-phonon coupling. The findings are not only important for developing high-power radiation-balanced lasers, but are also promising for manufacturing ultraefficient solid-state laser coolers.

Phonon‐Assisted Anti‐Stokes Lasing in ZnTe Nanoribbons

Photon upconversion is a photophysical process in which two low-energy photons are converted into one high-energy photon. Photon upconversion has broad appeal for a range of applications from biomedical imaging and targeted drug release to solar energy harvesting. Current upconversion nanosystems, including lanthanide-doped nanocrystals and triplet–triplet annihilation molecules, have achieved upconversion quantum yields on the order of 10–30%. However, the performance of these materials is hampered by inherently narrow absorption cross sections and fixed energy levels originating in atomic, ionic, or molecular states. Semiconductors, on the other hand, have inherently wide absorption cross sections. Moreover, recent advances enable the synthesis of colloidal semiconductor nanoparticles with complex heterostructures that can control band alignments and tune optical properties. We synthesize and characterize a three-component heterostructure that successfully upconverts photons under continuous-wave illumi...

Engineering Efficient Photon Upconversion in Semiconductor Heterostructures.

The influence of O2 flow rate on the compositional, optical and electrical characteristics of silicon oxide (SiOx) thin films (x < 2) were studied in this work. The SiOx thin films were obtained by pulsed direct current (DC) magnetron sputtering (PMS) onto n-type Si wafers (and also on glass substrates) at a vacuum of 3 × 10−3 Pa. Rutherford backscattering spectrometry (RBS) was used to check the compositional elements of deposited films and its oxidized states were analysed via Fourier-transform infrared (FTIR) spectroscopy. The optical properties of as-deposited SiOx thin films were investigated from transmittance measurements at room temperature in the wavelength range of 250–800 nm. The obtained data reveal that the Urbach energy (a measure of the band tail extension, Eu) decreased from about 523 to 172 meV as the rate of oxygen gas flow increased. On the contrary, the optical energy band-gap (Eg) increased from 3.9 to 4.2 eV. Conduction and valance band positions (relative to the normal hydrogen electrode) were also evaluated. The observed behavior is probably associated with the degree of disorder and defects presented in the as-deposited SiOx thin films, probably due to the presence of newly inserted oxidized OnSiHy species resulting from some contamination with water vapor desorbed from the walls of the deposition vacuum chamber. After deposition of a gold top electrode, the electrical characteristics of the fabricated Au/SiOx/n-Si system (i.e., a metal/insulator/semiconductor structure—MIS) were studied via characteristic I-V curves and their dependence upon the O2 flow rate are reported. It was observed that the Au/SiOx/n-Si structure behaves like a Schottky-diode exhibiting a very good diode rectifying performance with a rectification ratio of at least 300 and up to 104, which refers to the samples produced with the lower and higher O2 flow rates, respectively. It was also found that the O2 flow rate influences the rectifying performance of the SiOx/n-structures since both the diode ideality factor, n, and the diode series-resistance, RS decreases with the increase of O2 content, possibly reflecting a closer approximation to a full stoichiometric condition.

https://www.mdpi.com/2079-6412/9/8/468/pdf

Compositional, Optical and Electrical Characteristics of SiOx Thin Films Deposited by Reactive Pulsed DC Magnetron Sputtering

Defect absorption and optical transitions in hydrogenated amorphous silicon

We report the results of the optical spectra modeling for hydrogenated amorphous silicon (a-Si:H) thin films produced for photovoltaic cell applications, which allowed us to accurately determine the material’s optical gap (Eg). While for thick films of a-Si:H, as well as for other amorphous semiconductors, Eg is normally estimated from a so called Tauc plot, this is hardly possible for thin films because of the interference effects. We developed a physically founded semianalytical model for the complex dielectric function of a-Si:H, valid below and above the optical gap and containing a small number of adjustable meaningful parameters, including Eg and the characteristic energy scales of the optical transition matrix element distribution and the joint density of states in the absorption tail region. With this model and using the transfer matrix formalism for multilayer optics, we have achieved a good agreement between the calculated and experimental transmittance spectra, which allowed us to self-consiste...

Dielectric function of hydrogenated amorphous silicon near the optical absorption edge

We present the theory of the thermally activated photoluminescence upconversion, also known as anti-Stokes photoluminescence (ASPL), based on the quantum dot (QD) polaron effect and explaining all the principal features of the ASPL in colloidal solutions of chemically grown nanocrystals (NCs). The results obtained by Monte-Carlo simulations reproduce all the experimentally observed ASPL trends in colloidal NC solutions and are being extended to dense QD systems, such as films composed by layers of closely packed NCs (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Cascade upconversion of photoluminescence in ensembles of II-VI semiconductor nanocrystals

/pdf/erratum-dielectric-function-of-hydrogenated-amorphous-4caz3yflca.pdf

Erratum: “Dielectric function of hydrogenated amorphous silicon near the optical absorption edge” [J. Appl. Phys. 106, 073110 (2009)]

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Dielectric function of hydrogenated amorphous silicon near the optical absorption edge

Cascade upconversion of photoluminescence in ensembles of II-VI semiconductor nanocrystals

Erratum: “Dielectric function of hydrogenated amorphous silicon near the optical absorption edge” [J. Appl. Phys. 106, 073110 (2009)]