Browsing by Author "Tiras, E."

Now showing 1 - 9 of 9

Open Access
Complementary and alternative technique for the determination of electron effective mass: Quantum hall effect
(Taylor & Francis Inc., 2016) Ardalı, S.; Tiras, E.; Arslan, E.; Özbay, Ekmel
The quantum Hall effect measurements in the AlInN/AlN/GaN heterostructure are studied in the temperature range from 1.8 K to 14 K and a magnetic field up to 11 T. The quantized two-dimensional electron gas was placed at the AlN/GaN interface. The Hall resistance of two-dimensional electron gas has been found to be quantized at multiple integers of von Klitzing constant that refers to the integer quantum Hall effect. The experimental data have been used to determine the Fermi energy, carrier density, and effective mass two-dimensional electrons. The results are in agreement with those derived from the longitudinal magnetoresistance in the same structure.
Open Access
Determination of scattering mechanisms in AlInGaN/GaN heterostructures grown on sapphire substrate
(Elsevier, 2021-01-27) Sonmez, F.; Arslan, Engin; Ardali, S.; Tiras, E.; Özbay, Ekmel
The electron mobility limited by different scattering mechanisms in the quaternary AlInGaN alloy grown on a GaN layer is investigated with the classical Hall measurement, which is performed at a temperature range of 12 and 350 K and a magnetic field of B = 0.51 T. The effect of the thickness and alloy composition of the quaternary AlInGaN layer on the mobility is also determined. The experimentally determined temperature-dependent Hall mobility was compared with mobility calculated by using Matthiessen's rule. The main scattering mechanisms, including acoustic phonon scattering (piezoelectric and deformation potential), polar optical phonon scattering, alloy disorder scattering, interface roughness scattering, ionized impurity scattering, dislocation scattering, background impurity scattering, were used in the calculations for all temperatures. The results show that the dominant scattering mechanisms, depending on the investigated sample, are the interface roughness scattering and alloy disorder scattering at almost all temperatures. At a low-temperature, mobility is limited by ionized impurity scattering. High-temperature mobility is limited by polar optical phonon scattering. Furthermore, our results suggest that the thickness and alloy composition of the quaternary AlInGaN layer should be optimized for better transport properties.
Open Access
Determination of the in-plane effective mass and quantum lifetime of 2D electrons in AlGaN/GaN based HEMTs
(2011) Celik O.; Tiras, E.; Ardali, S.; Lisesivdin, S.B.; Özbay, Ekmel
Magnetoresistance and Hall resistance measurements have been used to investigate the electronic transport properties of AlGaN/GaN based HEMTs. The Shubnikov-de Haas (SdH) oscillations from magnetoresistance, is obtained by fitting the nonoscillatory component to a polynomial of second degree, and then subtracting it from the raw experimental data. It is shown that only first subband is occupied with electrons. The two-dimensional (2D) carrier density and the Fermi energy with respect to subband energy (EF-E1) have been determined from the periods of the SdH oscillations. The in-plane effective mass (m*) and the quantum lifetime (τq) of electrons have been obtained from the temperature and magnetic field dependencies of the SdH amplitude, respectively. The in-plane effective mass of 2D electrons is in the range between 0.19 m0 and 0.22 m0. Our results for in-plane effective mass are in good agreement with those reported in the literature © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Open Access
Determination of the LO phonon energy by using electronic and optical methods in AIGaN/GaN
(Springer, 2012) Celik, O.; Tiras, E.; Ardali, S.; Lisesivdin, S. B.; Özbay, Ekmel
The longitudinal optical (LO) phonon energy in AlGaN/GaN heterostructures is determined from temperature-dependent Hall effect measurements and also from Infrared (IR) spectroscopy and Raman spectroscopy. The Hall effect measurements on AlGaN/GaN heterostructures grown by MOCVD have been carried out as a function of temperature in the range 1.8-275 K at a fixed magnetic field. The IR and Raman spectroscopy measurements have been carried out at room temperature. The experimental data for the temperature dependence of the Hall mobility were compared with the calculated electron mobility. In the calculations of electron mobility, polar optical phonon scattering, ionized impurity scattering, background impurity scattering, interface roughness, piezoelectric scattering, acoustic phonon scattering and dislocation scattering were taken into account at all temperatures. The result is that at low temperatures interface roughness scattering is the dominant scattering mechanism and at high temperatures polar optical phonon scattering is dominant.
Open Access
Effective mass of electron in monolayer graphene: Electron-phonon interaction
(AIP Publishing LLC, 2013-01-25) Tiras, E.; Ardali, S.; Tiras, T.; Arslan, E.; Cakmakyapan, S.; Kazar, O.; Hassan, J.; Janzén, E.; Özbay, Ekmel
Shubnikov-de Haas (SdH) and Hall effect measurements performed in a temperature range between 1.8 and 275 K, at an electric field up to 35 kV m -1 and magnetic fields up to 11 T, have been used to investigate the electronic transport properties of monolayer graphene on SiC substrate. The number of layers was determined by the use of the Raman spectroscopy. The carrier density and in-plane effective mass of electrons have been obtained from the periods and temperature dependencies of the amplitude of the SdH oscillations, respectively. The effective mass is in good agreement with the current results in the literature. The two-dimensional (2D) electron energy relaxations in monolayer graphene were also investigated experimentally. The electron temperature (Te) of hot electrons was obtained from the lattice temperature (TL) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss indicate that the energy relaxation of electrons is due to acoustic phonon emission via mixed unscreened piezoelectric interaction and deformation-potential scattering.
Open Access
Energy relaxation rates in AlInN/AlN/GaN heterostructures
(Springer, 2012-06-27) Tiras, E.; Ardali, S.; Arslan, E.; Özbay, Ekmel
The two-dimensional (2D) electron energy relaxation in Al0.83In0.17N/AlN/GaN heterostructures has been investigated experimentally. Shubnikov-de Haas (SdH) effect measurements were employed in the investigations. The electron temperature (T (e)) of hot electrons was obtained from the lattice temperature (T (L)) and the applied electric field dependencies of the amplitude of SdH oscillations. The experimental results for the electron temperature dependence of power loss are also compared with current theoretical models for power loss in 2D semiconductors. The power loss from the electrons was found to be proportional to (T (e) (3) - T (L) (3) ) for electron temperatures in the range 1.8 K < T (e) < 14 K, indicating that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. The effective mass and quantum lifetime of the 2D electrons have been determined from the temperature and magnetic field dependencies of the amplitude of SdH oscillations, respectively. The values obtained for quantum lifetime suggest that remote ionized impurity scattering is the dominant scattering mechanism in Al0.83In0.17N/AlN/GaN heterostructures.
Open Access
A novel hot carrier-induced blue light-emitting device
(Elsevier, 2021-05-24) Mutlu, S.; Erol, A.; Arslan, Engin; Özbay, Ekmel; Lisesivdin, S. B.; Tiras, E.
In this work, an InGaN/GaN multiple quantum well based Top-Hat Hot-Electron Light Emission and Lasing in a Semiconductor Heterostructure (Top-Hat HELLISH) is investigated. A heterojunction structure is designed based on an active InGaN quantum well placed in the n-type GaN region sandwiched by the n- and p-type GaN layers. The four quantum well structure of an InGaN/GaN heterojunction where the Indium ratio is 0.16 has been grown via Metal-Organic Chemical Vapor Deposition. In order to create an anisotropic potential distribution of the heterojunction, it is aimed to fabricate TH-HELLISH-GaN device in Top-Hat HELLISH (THH) geometry for four contacts with separate n- and p-channels. High-speed I-V measurements of the device reveal an Ohmic characteristic at both polarities of the applied voltage. Integrated EL measurements reveal the threshold of the applied electric field at around 0.25 kV/cm. The emission wavelength of the device is around 440 ± 1 nm at room temperature.
Open Access
Substrate effects on electrical parameters of Dirac fermions in graphene
(Elsevier, 2021-05-19) Tiras, E.; Ardali, S.; Firat, H. A.; Arslan, E.; Özbay, Ekmel
The substrate effects on the electronic transport properties of single-layer graphene on TiO2/Si substrate have been studied. The Hall mobility, sheet carrier density, and transport lifetime were obtained from the temperature-dependent Hall measurements, while the in-plane effective mass, quantum lifetime was obtained from the temperature-dependent variation of the Shubnikov de Haas (SdH) oscillations that were made at 1.8 to 45 K temperature range and up to the magnetic field of 11 T. The measurement results showed that in SLG/TiO2/Si sample, there were 2.36 ± 0.12x1016 m-3 amounts of 3D carriers coming from the substrate. In our previous studies, 3D carrier densities were measured as 6.07x1016 m-3 and zero for SLG/SiO2/Si and SLG/SiC sample, respectively. This result shows that the 3D carriers formed in the structure are significantly changed by a substrate. The scattering mechanisms were determined using the ratio. The ratio values obtained as 3.66. This value obtained was compared with the values we found for SLG/SiC (=1.36) sample and SLG/TiO2/Si (=3.08) sample our previous study. The results show that small-angle scattering is dominant in SLG/SiC sample, but large-angle scattering is dominant in SLG/SiO2/Si and SLG/TiO2/Si samples. The charged impurity scattering is the dominant scattering mechanism in SLG/TiO2/Si and SLG/SiO2/Si samples, whereas in SLG/SiC samples, a short-range scattering mechanism such as lattice defects can be said to affect the electronic transport.
Open Access
Temperature dependent energy relaxation time in AlGaN/AlN/GaN heterostructures
(2012) Tiras, E.; Celik O.; Mutlu, S.; Ardali, S.; Lisesivdin, S.B.; Özbay, Ekmel
The two-dimensional (2D) electron energy relaxation in Al 0.25Ga 0.75N/AlN/GaN heterostructures was investigated experimentally by using two experimental techniques; Shubnikov-de Haas (SdH) effect and classical Hall Effect. The electron temperature (T e) of hot electrons was obtained from the lattice temperature (T L) and the applied electric field dependencies of the amplitude of SdH oscillations and Hall mobility. The experimental results for the electron temperature dependence of power loss are also compared with the current theoretical models for power loss in 2D semiconductors. The power loss that was determined from the SdH measurements indicates that the energy relaxation of electrons is due to acoustic phonon emission via unscreened piezoelectric interaction. In addition, the power loss from the electrons obtained from Hall mobility for electron temperatures in the range T e > 100 K is associated with optical phonon emission. The temperature dependent energy relaxation time in Al 0.25Ga 0.75N/AlN/GaN heterostructures that was determined from the power loss data indicates that hot electrons relax spontaneously with MHz to THz emission with increasing temperatures. © 2012 Elsevier Ltd. All rights reserved.