H. Jafarzadeh ¹, M. Rezaee Rokn-Abadi ¹, H. Arabshahi ¹, N. Shahtahmasbi ¹

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad, IR

Abstract

In this article the effect of indium impurity on tin oxide layers sensitivity have been studied. Tin oxide thin films without impurity and with different impurities are deposited by spray pyrolysis method and their structural layers have been characterized by x-ray diffraction spectrum and SEM technology. In different temperature we have calculated layer sensitivity. It is found that the most sensitivity is in the sample of 6% impurity at temperature of 200°C. With increasing of impurity concentration the work temperature is decreased until in the 15% impurity sample the work temperature is decreased to 100°C.

Keywords

Tin Oxide, Spray Pyrolysis, Thin Films

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H. Arabshahi ¹, M. Rezaee Rokn-Abadi ¹, F. Badieeyan ¹, M. R. Khalvati ²

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad, IR
2 Physics Department, Shahrood University of Technology, Shahrood, IR

Abstract

Monte Carlo simulation of steady-state electron transport in ZnSe and ZnS diodes of n⁺-i(n)-n⁺ structure with a 0.2 µm active layer length is described. The anode voltage ranges from 1 to 5 V. The distributions of electron energies and electron velocities, and the profiles of the electron density, electric field, potential and average electron velocity are computed. Based on these data, the near ballistic nature of the electron transport in the 0.2 µm long diode and the importance of the back-scattering of electrons from the anode n⁺-layer are discussed. Also, the effects of the lattice temperature and doping on the length of the active layer are discussed. Our calculations show that electron reach to a higher drift velocity in the ZnSe than ZnS. So ZnSe material is a good candidate for high power device fabrication.

Keywords

Active Layer, Diode, Drift Velocity, Ballistic

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M. Mohammadi ¹, M. Rezaee Rokn-Abadi ¹, H. Arabshahi ¹

Affiliations
1 Dept. of Physics, Ferdowsi University of Mashhad, Mashhad, IR

Abstract

Aluminum doped ZnO (AZO) thin films have been prepared by spin coating route on glass substrate. The structural, optical and electrical thin films have been characterized in different post-heat temperatures between 45° and 600°C. Xray diffraction analysis has revealed hexagonal wurtzite structure with (002) preferred orientation which increased in crystallite size by increasing post-heat temperature. The optical spectra of the films showed the transmittance higher than 90% within the visible wavelength region. Our results show that optical gap and surface resistance of the films are decreased by increasing post-heat temperature.

Keywords

Sol-gel Method, Optical Spectra, Post-heat Temperature, Spin Coating

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H. Rezvani ¹, N. Shahtahmasebi ¹, M. Rezaee Rokn-Abadi ¹, H. Arabshahi ¹

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad, IR

Abstract

In this work, Cu-doped SnO₂ thin films were deposited by spray pyrolysis method. The films were prepared using SnCl₄ ,5H₂O and CuCl₂,2H₂O hydro-alcoholic solution. Then, the sensitivity parameter of SnO₂-based CO₂-gas sensors is studied for various atomic percentages ([Cu]/[Sn] = 0, 2, 4, 6, 10,12.5,15, 20, 25). In addition, the effect of substrate temperature on the sensing behavior of films was also studied. The XRD and SEM structural analysis of thin film sensors confirm the nano-structure of the films with SnO₂ cassiterite phase. The optical band gap of Cu doped- SnO₂ films were obtained from optical absorption spectra by UV-Vis absorption spectroscopy. Measurement of the electrical resistivity of films shows that with increasing of Cu-doping in films up to 12.5%, the electrical resistivity increase sharply.

Keywords

Thin Film, Gas-sensors, Metal-oxide, Tin-oxide, Nanostructure

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M. Mousavi ¹, A. Kompany ², M. Rezaee Roknabad ², H. Arabshahi ²

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad
2 Physics Department, Ferdowsi University of Mashhad, Mashhad, IN

Abstract

In this paper, various physical properties of ZnO piezoelectric crystal have been calculated by the methods of density functional theory and density functional perturbation theory. These tensors may be defined as second derivatives of an appropriately defined energy functional with respect to the atomic displacement, electric field or strain perturbations. We have calculated the electronic and mechanical properties of ZnO crystal such as band gap, elastic, compliance and piezoelectric tensors, and also bulk modulus of hexagonal phase. These calculations have been performed under boundary condition of constant electric field and zero temperature. The results show that hexagonal ZnO has a direct band gap of 0.82 eV, its elastic tensor for the frozen-ion is smaller than the relaxed-ion and the diagonal values of frozen-ion compliance tensor S are larger than relaxed-ion ones. The calculated properties are in good agreement with the reported experimental results.

Keywords

Band Structure, Elastic Tensor, Piezoelectric Tensor, Bulk Module

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H. Arabshahi ¹

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad, IR

Abstract

An ensemble Monte Carlo simulation have been carried out to study temperature and doping dependencies of electron drift velocity in ZnS, GaN and 6H-SiC. We study how electrons, initially in thermal equilibrium, drift under the action of an applied electric field within bulk of these materials. Calculations are made using a non-parabolic effective mass energy band model, Monte Carlo simulation that includes all of the major scattering mechanisms. The band parameters used in the simulation are extracted from optimized pseudopotential band calculations to ensure excellent agreement with experimental information and ab-initio band models. For all materials, it is found that electron velocity overshoot only occurs when the electric field is increased to a value above a certain critical field, unique to each material. This critical field is strongly dependent on the material parameters. Transient velocity overshoot has also been simulated, with the sudden application of fields up to 600 kVm^-1, appropriate to the gate-drain fields expected within an operational field effect transistor. The electron drift velocity relaxes to the saturation value of about 1.5×105 ms^-1 within 3 ps, for all crystal structures.

Keywords

Ensemble Monte Carlo, Drift Velocity, Transient Velocity, Pseudopotential

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H. Arabshahi ¹, M. Rezaee Rokn-Abadi ¹

Affiliations
1 Physics Department, Ferdowsi University of Mashhad, Mashhad, IR

Abstract

A Monte Carlo simulation has been used to model steady state and transient electron transport in 6H-SiC field effect transistor. The simulated device geometries and doping are matched to the nominal parameters described for the experimental structures as closely as possible and the predicted I-V and transfer characteristics for the intrinsic devices show fair agreement with the available experimental data. Simulations of the effect of modulating the gate bias have also been carried out to test the device response and derived the frequency bandwidth. Value of 90±10 GHz has been derived for the intrinsic current gain cut-off frequency of the 6H-SiC MESFETs.

Keywords

Steady-state, Transient, Cut-off Frequency, Frequency Bandwidth

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A. Mokhles Gerami ¹, H. Rahimpour Soleimani ¹, H. Arabshahi ², M. R. Khalvati ³

Affiliations
1 Dept. of Physics, Univ. of Guilan, Rasht, IR
2 Dept. of Physics, Ferdowsi Univ. of Mashhad, Mashhad, IR
3 Department of physics, Shahrood University of Technology, Shahrood, IR

Abstract

An ensemble Monte Carlo simulation has been carriedout to study electron transport properties in GaP, InP and Ga0.5In0.5P materials. The simulation results show that intervalley electron transfer plays a dominant role in higher electric fields leading to a strongly inverted electron distribution and to a large negative differential conductance. In addition, the electron velocity in GaP is less sensitive to temperature than other group III-V semiconductors like InP and Ga0.5In0.5P. So GaP devices are expected to be more tolerant to self-heating and high ambient temperature device modeling.

Keywords

Ensemble Monte Carlo, Polar Optical Phonons, Deformation Potential, Self-heating

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