T. Asar

Dielectric spectroscopy studies and ac electrical conductivity on (AuZn)/TiO2/p-GaAs(110) MIS structures

In this study, we investigated temperature and voltage dependence of dielectric properties and ac electrical conductivity (σac) of (AuZn)/TiO2/p-GaAs(110) metal–insulator–semiconductor structures in the temperature range of 80–290 K using the capacitance–voltage and conductance–voltage measurements at 1 MHz. The intersection/crossing behaviour of C–V plots at sufficiently high forward biases and the increase in σac with increasing temperature was attributed to the lack of sufficient number of enough free charge carriers at low temperatures. The values of the dielectric constant (ε′), dielectric loss (ε″), loss tangent , ac electrical conductivity (σac), the real and imaginary parts of electric modulus () were found to be strong functions of temperature and applied bias voltage. The Cole–Cole plots between have shown only one semicircle for each temperature. This indicates one of the relaxation processes was suppressed and this can be attributed to the surface polarization effect. On the other hand, plot has a peak for each temperature. The plots revealed two linear regions with different slopes for sufficiently high forward biases (0.0, 0.5, and 1.0 V) which correspond to low (80–200 K) and moderate/intermediate (230–290 K) temperatures. Thus, the values of activation energy (Ea) were obtained from the slope of these Arrhenius plots for two linear regions as 87.3 and 3.4 meV, respectively, at 1.0 V. On the other hand, Mott plots have only one linear region except for 260 and 290 K and Mott parameters were determined from these plots at 0.0, 0.5 and 1.0 V.

Structural and electrical characterizations of InxGa1-xAs/InP structures for infrared photodetector applications

Three InGaAs/InP structures for photodetector applications were grown with different indium compositions by MBE technique. The structural properties of the samples have been obtained by means of high resolution X-ray diffraction and secondary ion mass spectrometry measurements. Three InGaAs/InP metal-semiconductor-metal devices were fabricated at room temperature. The experimental forward and reverse bias current–voltage characteristics of the devices such as ideality factor, barrier height, and saturation current were evaluated considering the structural properties of the grown structures. The carrier recombination lifetime and diffusion length in the devices were also calculated using carrier density and mobility data obtained with Hall effect measurement at room temperature. It was determined that all room temperature fabricated devices improved the Schottky barrier height. Especially, the device fabricated on the lower mismatched structure exhibited barrier height enhancement from 0.2 eV, which is the...

Effect of platinum doping on the structural and electrical properties of SnO2 thin films

ABSTRACT The investigation of Pt doping effect on the structural and electrical properties of SnO2 thin films was aimed in this study. For this purpose, the polycrystalline pure and Pt-doped SnO2 thin films were deposited onto n-type silicon substrate and the Pt sputter power was varied as 0 (un-doped), 2, 5 and 7 W by using radio frequency confocal sputtering system. The structural properties of the samples were analysed by X-ray diffraction measurements. The structural results show that the 5 W Pt-doped SnO2 sample has better crystallinity than the other samples. The results of the electrical measurements as current–voltage, capacitance–voltage and conductance–voltage were also obtained and discussed in detail for fabricated diodes. The analysis of electrical characteristics shows that the use of different Pt doping has significant effect on electrical properties of such devices. The study also provides an improved supplemental understanding to the related technologies which use Pt-doped SnO2 materials.

Study on growth and characterizations of GaxIn1−xP/GaAs solar cell structure

GaxIn1−xP/GaAs solar cell (SC) structure was grown on p-type (100)-oriented GaAs substrate by using solid-source molecular beam epitaxy technique. The structural, optical and morphological properties of GaxIn1−xP/GaAs SC structure have been evaluated by means of high resolution X-ray diffraction, photoluminescence, spectroscopic ellipsometry and atomic force microscopy measurements at room temperature. In addition, GaxIn1−xP/GaAs SC structure was fabricated for obtaining the cell’s electrical output parameters. For this purpose, the current–voltage characteristics of GaxIn1−xP/GaAs SC structure were performed and analyzed at the room temperature under both dark and illuminations by using air mass global 1.5 (AM1.5) solar simulator. The device parameters such as the open-circuit voltage, the short-circuit current (Isc), the fill factor and the energy convertion efficiency (η) of GaxIn1−xP/GaAs SC structure were extracted from the current–voltage characteristics.

Modelling of a Cd1−xZnxTe/ZnTe Single Quantum Well for Laser Diodes

In this paper, the carrier density, temperature and quantum well width effect have been investigated for the optical gain for a Cd1−xZnxTe/ZnTe Zinc-blend strained quantum well structure. The device emits laser radiations in green–yellow–orange. Our results showed that the optical gain significantly increases with the increasing of the carrier density. It also increases with the decreasing of the Zn concentration, the well width and the temperature. In addition, the optimal threshold current density values were determined for three alloy compositions as 0.7, 0.8 and 0.9.

Investigation of structural and electrical properties of Zirconium dioxide thin films deposited by reactive RF sputtering technique

ABSTRACT ZrO2 thin films with different thicknesses (400 nm, 500 nm, 600 nm) were deposited by reactive RF magnetron sputtering technique, on n-type Silicon (100) substrate at 200°C applying 125 W power ratin`g. The micro structural properties of thin films were obtained by Scanning Electron Microscope and it was observed that the films were grown successfully in the form of big grains formed by the accumulation of small particles. It was seen that the size of grains changed with the increase of film thickness. Energy-dispersive X-Ray spectroscopy was used to determine the chemical compositions of samples. The crystal structures of ZrO2 samples were analyzed by X-ray diffraction technique. In addition, the Current-Voltage and Capacitance-Voltage measurements were completed to investigate the electrical properties of samples.

Efficiency improvement of quantum well solar cell with the AuGeNi metallization and Si3N4 ARC design

This study demonstrates the power conversion efficiency enhancement on In0.19Ga0.81As/GaAs quantum well solar cells (QWSC). The solar cell structure was grown on n-type (100)-oriented GaAs substrate by using solid-source molecular beam epitaxy technique and divided into square pieces. In order to understand whether the eight quantum wells were grown or not, scanning electron microscopy (SEM), and secondary ion mass spectrometry characterizations were done at room temperature. After that, the Si3N4 antireflection layers were coated onto both two square pieces of In0.19Ga0.81As/GaAs QWSC structure and p-GaAs substrate at different temperatures by the radio frequency magnetron sputtering system. The optical properties of the Si3N4 coated and uncoated p-GaAs samples have been evaluated by means of ultraviolet-visible spectrometry measurements at room temperature. According to ultraviolet-visible spectrometry results, the best Si3N4 antireflection coated one was obtained at 100 °C substrate temperature. Thus, the In0.19Ga0.81As/GaAs QWSC structure with and without Si3N4 layer, which was coated at 100 °C substrate temperature, was selected for other measurements and processes. Moreover, the In0.19Ga0.81As/GaAs QWSC samples with and without Si3N4 antireflection coating were separately fabricated with different metallization materials for obtaining the solar cell electrical output parameters. AuGe and AuGeNi metallization materials were used for the fabrication processes. After fabrication, the electrical output parameters were extracted from the current-voltage measurements at room temperature both in dark and under AM1.5 – 1 Sun illumination. The proposed design which includes the AuGeNi metallization and Si3N4 antireflection layer enhanced the power conversion efficiency by 44.40%.

Erratum to: Modelling of a Cd1−xZnxTe/ZnTe Single Quantum Well for Laser Diodes

1.—Faculty of Science, University of Batna and Laboratory of Metallic and Semiconductor Materials (LMSM) University Biskra, Biskra, Algeria. 2.—Research Centre in Industrial Technologies CRTI, P.O. Box 64, 16014 Cheraga, Algiers, Algeria. 3.—Department of Physics, Faculty of Sciences, Gazi University, 06500 Ankara, Turkey. 4.—Photonics Application and Research Center, Gazi University, 06500 Ankara, Turkey. 5.—e-mail: trkasar@gazi.edu.tr