فهرست مطالب

Optoelectronical Nanostructures - Volume:3 Issue: 2, Spring 2018

Journal of Optoelectronical Nanostructures
Volume:3 Issue: 2, Spring 2018

  • تاریخ انتشار: 1397/04/20
  • تعداد عناوین: 7
|
  • Sohrab Manouchehri *, Javad Zahmatkesh, Mohammad Hassan Yousefi Pages 1-18
    Nanocrystalline PbS thin films are deposited on glass and alumina substrates through the chemical bath deposition technique by creating similar conditions, in order to investigate the effects of the substrate. The structural and optical properties of PbS films are investigated by X-ray diffraction, scanning electron microscope, and UV–Vis. The structural analyses of the films indicate that they are of polycrystalline configurations and have a face-centered-cubic (fcc) rock-salt structure on different substrates. The X-ray diffraction shows that the structure peaks occur at slightly higher angles in the deposited (grown) films on glass substrate than the ones deposited on alumina substrate. Crystal parameters are exceptionally affected by the type of substrate as well. SEM images reveal that the surface morphology of the PbS thin films is quite dependent upon the nature of the substrate. The optical band gaps of the samples are found to be 1.521 eV for glass and 1.678 eV for alumina substrates, which are higher in comparison to the bulk value (0.41 eV). According to the obtained results, PbS thin film on alumina substrate has narrower particle size distribution, better transmission and lower stress than PbS thin film on glass substrate.
    Keywords: Chemical Bath Deposition, optical properties, Pbs Thin Film, Structural Properties, Substrate
  • Heydar Izadneshan *, Ghahraman Solookinejad Pages 19-28
    Cu2ZnSnS4 (CZTS) thin films were prepared by directly sputtering Cu (In,Ga)Se2 quaternary target consisting of (Cu: 25%, Zn: 12.5%, Sn; 12.5% and S: 50%). The composition and structure of CZTS layers have been investigated after annealing at 200 0C, 350 0C and 500 0C under vacuum. The results show that recrystallization of the CZTS thin film occurs and increasing the grain size with a preferred orientation in the (112) direction was obtained. The Raman spectra showed the existence of crystalline CZTS phase after annealing. Optical transmission spectra were recorded within the range 300-900 nm. The energy band gap (Eg) of the CZTS thin films was calculated before and after annealing from the transmittance spectra using Beer-Lambert’s law. Results show that Eg is dependent on the annealing temperature. The optical band gap of CZTS also varied from 1.57 eV to 1.31 eV with increase in the annealing temperature from 200 0C min to 500 0C.
    Keywords: CZTS, Magnetron Sputtering, optical properties, Solar Cells
  • Arash Rezaei *, Bahram Azizollah-Ganji, Morteza Gholipour Pages 29-40
    Field Effect Diode (FED)s are interesting device in providing the higher ON-state current and lower OFF–state current in comparison with SOI-MOSFET structures with similar dimensions. The impact of channel length and band-to-band tunneling (BTBT) on the OFF-state current of the side contacted FED (S-FED) has been investigated in this paper. To find the lowest effective channel length, this device is simulated with 75, 55 and 35 nm channel length and the results obtained are presented in this article. Our numerical results show that the ION/IOFF ratio can be varied from 104 to 100 for S-FED as the channel lengths decrease. We demonstrate that for channel lengths shorter than 35 nm by considering the Band-to-Band tunneling model, the SFED device does not turn off.
    Keywords: Field Effect Diode (FED), Side Contacted FED (S-FED), Band-To- Band-Tunneling (BTBT), ION-IOFF Ratio
  • Mahdi Bahadoran * Pages 41-52
    The buried hetero-structure (BH) InGaAsP-InP waveguide is used for a system of double microring resonators (DMR). The light transmission and location of resonant peaks are determined for six different sets of ring radii with different order mode numbers. The effect of changing middle coupling coefficient on the box like response is studied. It is found that the surge of coupling coefficient to the lower values makes the through port resonance peaks sharper and for a larger amount of middle coupling values, the transmission decreases according to the order mode numbers. The DMR design with a small middle coupling and close values for rings perimeters can generate practical pass bandwidth of the resonant transmission peak. Moreover, any modification in resonant mode numbers and middle coupling coefficient can change the width and height of the box like response. A DMR simulated results with the free spectral range (FSR) of 10.2 nm is validated by comparing with the experimental data. Achieved results are practical in the filtering process of optical communication.
    Keywords: Double Ring Resonator, Microring Resonator, Signal Flow Graph, Optical Filter
  • Hamdollah Salehi, Peiman Amiri, Rohollah Zare Hasanabad * Pages 53-64
    In this work we investigate the electronic, optical, dynamic and thermoelectric properties of ternary copper-based Chalcogenides CuSbX2 (X= S, Se) compounds. Calculations are based on density functional theory and the semi-classical Boltzmann theory. Computations have been carried out by using Quantum-Espresso (PWSCF) package and ab-initio pseudo-potential technique. To estimate the exchange-correlation functional various approximations were used,which among them GGA approximation led to better results. Density of state calculations indicates that CuSbSe2 and CuSbS2 compounds are semiconductors with a band gap of about 0.81 eV and 0.62 eV respectively. A lack of negative frequencies in the phonon dispersion curves of these compounds shows the stability of the compounds. The static refractive indices of CuSbSe2 compound are 4.38, 3.66 and 3.30 calculated within GGA, GGA and GGAmBJ approximations respectively and plasmon frequencies obtained from the peak of the loss function is occurred at energies around 16eV.A trend of electrical conductivity behavior against temperature verify the semiconducting n
    Keywords: Density functional theory, optical properties, thermodynamic properties, semiconductor
  • Mehdi Riahinasab *, Elham Darabi Pages 65-86
    The frequency behavior of the tunnel injection quantum dot vertical cavity surface emitting laser (TIQD-VCSEL) is investigated by using an analyticalnumerical method on the modulation transfer function. The function is based on the rate equations and is decomposed into components related to different energy levels inside the quantum dot and injection well. In this way, the effect of the tunneling process on the improvement of the laser frequency response is determined. Generally, the components of the modulation transfer function in the wetting layer and the excited state limit the total laser bandwidth. Of course, the component associated with the tunneling process increases overall system bandwidth. It is shown that for currents above threshold, the carrier density at the excited state in TIQD has a slight slope, unlike the conventional quantum dot (CQD). It will improve the frequency response of the tunnel injection structure. It can be attributed to the difference in Pauli blocking factor values at the excited state and the ground state in the two structures.
    Keywords: Modulation Transfer Function, Tunnel Injection Quantum Dot (TIQD), Vertical Cavity Surface Emitting Laser (VCSEL)
  • Alireza Keshavarz *, Mohama Jalal Soltanzadeh Pages 87-96
    In this paper, the optimal Fresnel lenses are designed by Zemax software. The fundamental problem of the Fresnel lenses is the beam divergence, which was resolved by decreeing the output stain diameter on the image plane. For this purpose, two types of radial and cylindrical Fresnel lenses are simulated with different grooves using Global and Hammer optimization methods. The minimum output stain diameter in radial and cylindrical modes are computed for Fresnel surfaces and different components of the Fresnel lenses. The Results show that the Fresnel lenses have a spherical and distortion aberration. By optimizing the optical system with the Global and Hammer methods, the output stain diameter can be controlled and the beams are focused. Numerical results and conclusions are given in our paper by changing the distance between the elements, radius, material, height, depth and width
    Keywords: Fresnel Lenses, Optimization, Stain Diameter, Hammer, Global Method