II-VI wide bandgap semiconductors

Pure tin dioxide (SnO2) and Al doped SnO2 nanoparticles are prepared by co-precipitation method. Studies on
structural and morphological properties are done by X-ray diffraction, field emission scanning electron microscopy and
electron diffraction X-ray spectroscopy and optical properties by using UV–Visible spectroscopy in diffuse reflectance
spectroscopy mode. Porosity is found to increase with Al doping when compared to pure SnO2. The band gap as well as
Urbach energy increases with Al doping. Al doped SnO2 exhibits high porosity.

In this work we propose a simple empirical rule for the absorption coefficient of mercury cadmium telluride (MCT), valid both in the non-degenerate and in the degenerate case. The rule takes into account the Urbach band tailing and non-parabolicity of bands. Additionally, an expression is proposed for the Moss-Burstein effective bandgap spreading in degenerate narrow-band semiconductors. The results are compared to the available experimental data on MCT and to the results of numerical calculation obtained by the Kane model. A critical comparison is made between the proposed rules and the standard approximations used to describe the MCT absorption coefficient

In this paper, we report room-temperature fer-romagnetism in chemically synthesized Zn 1-x Co x S (0 B x B 0.10) diluted magnetic semiconductor nanopar-ticles of *3–5 nm. The incorporation of Co 2? ion for Zn 2? ions in ZnS lattice and the particle size were confirmed by XRD and TEM along with selected area electron diffraction analysis. UV–Vis measurement showed reduction in the bandgap energy with the increase in Co doping. Maximum magnetization was observed for samples with x = 0.04. From photoluminescence, spectra luminescence efficiency was found to get enhanced on Co doping. Magnetization behavior can be understood to be due to defect-induced ferromagnetism; however, for higher doping concentration, the antiferromagnetic coupling of Co– Co interaction in the close proximity results in the decrease of the overall magnetization of the samples. Moreover, magneto-electronic study also showed a maximum negative magneto-resistance of *43 % for x = 0.04.

In this study, praseodymium barium cobalt oxide nanofiber interfacial layer was sandwiched between Au and n-Si. Frequency and voltage dependence of e 0 , e 0 , tand, electric modulus (M 0 and M 00) and r ac of PrBaCoO nanofiber capacitor have been investigated by using impedance spectroscopy method. The obtained experimental results show that the values of e 0 , e 0 , tand, M 0 , M 00 and r ac of the PrBaCoO nanofiber capacitor are strongly dependent on frequency of applied bias voltage. The values of e 0 , e 00 and tand show a steep decrease with increasing frequency for each forward bias voltage, whereas the values of r ac and the electric modulus increase with increasing frequency. The high dispersion in e 0 and e 00 values at low frequencies may be attributed to the Maxwell–Wagner and space charge polarization. The high values of e 0 may be due to the interfacial effects within the material, PrBaCoO nanofibers interfacial layer and electron effect. The values of M 0 and M 00 reach a maximum constant value corresponding to M 1 % 1/e 1 due to the relaxation process at high frequencies, but both the values of M 0 and M 00 approach almost to zero at low frequencies. The changes in the dielectric and electrical properties with frequency can be also attributed to the existence of N ss and R s of the capacitors. As a result, the change in the e 0 , e 00 , tand, M 0 , M 00 and ac electric conductivity (r ac) is a result of restructuring and reordering of charges at the PrBaCoO/n-Si interface under an external electric field or voltage and interface polarization.

Group IV (Si, Ge, Sn) alloys are promising materials for future optoelectronic devices. Their compatibility with Si technology would allow us to engineer novel growth techniques and bandgap engineering methods to obtain direct band gap materials. Other alloy compositions could allow wider wavelength range which can revolutionize the photonics industry - leading to new design of LEDs, photodetectors, laser diodes and electro optical modulators.
In this paper, we study one such possible structure - self assembled Ge QDs embedded on Si0.5Ge0.5 virtual substrate with the same capping layer. A wetting layer is considered to simulate the actual scenario. Then we conduct a theoretical study on the strain and electronic band structure of this model. We employ the valence force field (VFF) method using Keating potential to estimate the strain followed by 8 band k∙p method to calculate the electronic band structure taking the 𝛤 valley into consideration. Finally we study the optical gain of the system for varying carrier concentrations.

We demonstrate high performance chemical bath deposited CdS thin-film transistors (TFTs) using atomic layer deposited ZrO2 based high-k gate dielectric material. Our unique way of isolation of the CdS-based TFTs devices yielded significantly low leakage current as well as remarkable lower operating voltages (<5 V) which is four times smaller than the devices reported on CdS-based TFTs using SiO2 gate dielectric. Upon thermal annealing, the devices demonstrate even higher performance, including μFE exceeding 4 ± 0.2 cm2 V−1S−1, threshold voltage VT of 3.8 V, and Ion-off of 104–105, which hold much promise for applications in future electronic and optical devices.

Phase change of cubic ZnS to hexagonal ZnO via heat treatment.Band gap was found to decrease with increasing calcinations temperature.ZnO samples have higher magnetic moment than ZnS.Blocking Temperature of the samples is well above room temperature.Maximum negative %MR with saturation value ∼38% was found for sample calcined at 600° C.The present work concentrates on the synthesis of cubic ZnS and hexagonal ZnO semiconducting nanoparticle from same precursor via co-precipitation method. The phase conversion of ZnS to highly crystalline hexagonal ZnO was done by heat treatment. From the analysis of influence of calcination temperature on the structural, optical and vibrational properties of the samples, an optimum temperature was found for the total conversion of ZnS nanoparticles to ZnO. Role of quantum confinement due to finite size is evident from the blue shift of the fundamental absorption in UV-vis spectra only in the ZnS nanoparticles. The semiconducting nature of the prepared samples is confirmed from the UV-vis, PL study and transport study. From the magnetic and transport studies, pure ZnO phase was found to be more prone to magnetic field.The phase conversion of ZnS to highly crystalline hexagonal ZnO was done by heat treatment.

The electronic band structure and optical gain of GaN x Bi y As 1−x−y /GaAs pyramidal quantum dots (QDs) are investigated using the 16-band k·p model with constant strain. The optical gain is calculated taking both homogeneous and inhomogeneous broadenings into consideration. The effective band gap falls as we increase the composition of nitrogen (N) and bismuth (Bi) and with an appropriate choice of composition we can tune the emission wavelength to span within 1.3 µm–1.55 µm, for device application in fiber technology. The extent of this red shift is more profound in QDs compared to bulk material due to quantum confinement. Other factors affecting the emission characteristics include virtual crystal (VC), strain profile, band anticrossing (BAC) and valence band anticrossing (VBAC). The strain profile has a profound impact on the electronic structure, specially the valence band of QDs, which can be determined using the composition distribution of wave functions. All these factors eventually affect the optical gain spectrum. With an increase in QD size, we observe a red shift in the emission energy and emergence of secondary peaks owing to transitions or greater energy compared to the fundamental transition.

The work presents an approximate expression for refractive index of mercury cadmium telluride (Hg1-xCdxTe) applicable to both intrinsic and degenerate material. The relation is applicable for cadmium mole fractions x = 0.165-1 at 300 K and 0.165-0.54 at 77 K and electron concentrations up to 1017 cm-3. The results are compared to available experimental data and to the results of calculation using Kramers-Kronig relation. A unified expression for interband absorption coefficient based on the Kane three-band model was used in the calculation, whilst the Urbach band-tailing and the electron-electron interaction were also taken into account.