Verification of influence of tail states and interface states on sub-threshold swing of Si n-channel MOSFETs over a temperature range of 4K to 300K

We experimentally characterize SS of Si nMOSFETs with a substrate boron concentration of 2 × 1016 cm-3 as a function of IDS and temperatures from 4 to 300 K to verify the validity of the physical model of SS. The minimum SS are obtained around 4 mV/dec. at 4 K. The physical model including band tail states and interface states is employed to represent the experimental SS from 4 to 300 K. The impact of each parameter included in the physical model on SS behavior is examined by changing the value of the parameters in simulation. It is found that the proposed physical model can quantitatively represent experimental SS in a wide range of IDS and temperature under a given set of the parameters regarding the band tail states and the interface states. This finding indicates the validity of the present physical model and the correctness of the physical picture.

Structural and Band Structure Investigation of Iron Oxide Nanoparticles Incorporated PVA Nanocomposite Films

The work reported here deals with the fabrication and characterization of iron oxide (Fe3O4) nanoparticles (NPs – IONPs) incorporated polyvinyl alcohol (PVA)-based nanocomposite films. The nanocomposite films, fabricated via solution casting route, have been characterized using advanced analytical techniques including x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and UV-visible (vis.) spectroscopy. There observed notable changes in the structural phases, crystallite size (2.3 to 2.1 nm), d-spacing (0.131 to 0.134 Å), optical absorption edge (5.12 to 4.84 eV), indirect bandgap (4.99 to 4.68 eV), direct bandgap (5.35 to 5.20 eV), and band tail (0.57 to 0.89 eV) from native PVA to nanocomposite films. The refractive index and optical conductivity enhancements were also observed on incorporating IONPs into the PVA matrix. It could be inferred that a minute loading of IONPs might induce significant alternation in opto-structural properties of the PVA-based nanocomposites for potential optoelectronic applications.

Influence of chemical composition and doping on optical properties of thallium selenide layers prepared by adsorption/diffusion method

In this work, we investigated the formation of Tl-Se layers followed by doping with metal cations. A two-stage adsorption/diffusion process used to form Tl-Se layers involves (a) selenization in potassium selenotrithionate solution followed by (b) treatment with Tl+ precursor solutions. These layers have been successfully doped with Cu+/Cu2+, Ga3+ and Ag+ cations using a cation exchange reaction. The resulting chemical compositions of Tl-Se and Tl-M-Se (M = Cu, Ga, Ag) layers were investigated using the EDS and AAS methods. The bulk elemental composition and the Tl/Se molar ratio of the Tl-Se layers varied with the concentration of the Tl+ precursor solution, the exposure time in the Tl+ precursor solution, and the form of the Tl+ in the solution, whereas the EDS analysis showed that the surface was slightly enriched in thallium. The optical properties of the formed layers were studied. These layers were identified using room temperature reflection spectrum, the values of absorption edge, bandgap (Eg), band tail width (Urbach energy, EU) of the localised states, Steepness parameter (σ) and electron–phonon interaction (Ee-p).

Optical Bandgap Definition via a Modified Form of Urbach’s Rule

We are reporting an esoteric method to determine the optical bandgap of direct gap materials by employing Urbach’s rule. The latter, which describes the slope of the band tail absorption in semiconductors, in its original version, cannot be employed to pinpoint the optical bandgap. Herein, however, we show that a modified form of Urbach’s rule defines the optical bandgap, and therefore, enables the accurate determination of the optical bandgap energy, which turns out to be identical with the threshold energy for the band tail absorption. The model further produces an explicit expression for the absorption coefficient at the optical bandgap energy.

Polarization-Sensitive Light Sensors Based on a Bulk Perovskite MAPbBr3 Single Crystal

Organic-inorganic halide perovskites have attracted much attention thanks to their excellent optoelectronic performances. Here, a bulk CH3NH3PbBr3 (MAPbBr3) single crystal (SC) was fabricated, whose temperature and light polarization dependence was investigated by measuring photoluminescence. The presence of obvious band tail states was unveiled when the applied temperature was reduced from room temperature to 78 K. Temperature dependence of the bandgap of the MAPbBr3 SC was found to be abnormal compared with those of traditional semiconductors due to the presence of instabilization of out-of-phase tail states. The MAPbBr3 SC revealed an anisotropy light absorption for linearly polarized light with an anisotropy ratio of 1.45, and a circular dichroism ratio of up to 9% was discovered due to the spin-orbit coupling in the band tail states, exhibiting great polarization sensitivity of the MAPbBr3 SC for the application of light sensors. These key findings shed light on the development of potential optoelectronic and spintronic applications based on large-scaled organic-inorganic perovskite SCs.

The Optical Blueshift Saturation Behavior of Mg-=SUB=-x-=/SUB=-Zn-=SUB=-1-x-=/SUB=-O Films

A phenomenon of blueshift saturation was observed from cathodoluminescence (CL) spectra of MgxZn1-xO films (0.069≤x≤0.8) which were grown by pulsed laser deposition technology. By analyzing the results of composition-dependent X-ray diffraction spectra, scanning electron microscopy images, absorption spectra and CL spectra, the crystalline structural disorder was determined via Urbach energy value. Furthermore, a competition mechanism between band-filling effect and band tail states was proposed in the composition-dependent CL spectra. This competition is believed to be responsible for the composition-induced blueshift saturation often observed in the disordered alloy semiconductors. The results of this research can provide important reference in energy-band engineering.