(2) Photonics Research Center
Gazi University, Ankara, Turkey 06500
Phone: +90 312 202 1391
New grant received from TUBITAK/RFBR 2532 coded international collaboration programme.
7 February 2014
We received the joint grant of Scientific and Technological Research Council of Turkey (TUBITAK) and RFBR of Russia. Project is about manipulation of the properties of two-dimensional electronic gas using insitu surface passivation of AlGaN/GaN heterostructures by molecular beam epitaxy and will be held between 2014-2016. I am the project investigator of the project.
PhD, MSc and BSc positions available!
For more information please [click].
Selected Important Papers
Scattering Analysis of Extracted 2D carrier in AlGaN/GaN HEMT Structures
Hall effect measurements on undoped Al 0.25 Ga 0.75 N/GaN heterostructures grown by a metalorganic chemical vapour deposition (MOCVD) technique have been carried out as a function of temperature (20–350 K) and magnetic ﬁeld (0–1.5 T). Magnetic ﬁeld dependent Hall data were analysed using the quantitative mobility spectrum analysis (QMSA) technique. The mobility and density within the two-dimensional electron gas (2DEG) at the Al 0.25 Ga 0.75 N/GaN interface and within the underlying GaN layer were successfully separated by QMSA. Mobility analysis has been carried out using both the measured Hall data at a single ﬁeld and the extracted data from QMSA. Analysis of the temperature-dependent mobility of 2DEG extracted from QMSA indicates that the interface roughness and alloy disorder scattering mechanisms are the dominant scattering mechanisms at low temperatures while at high temperatures only polar optical phonon scattering is the dominant mechanism. Al 0.25 Ga 0.75 N/GaN interface related parameters such as well width, deformation potential constant and correlation length were also accurately obtained from the ﬁts of the simple analytical expressions of scattering mechanisms to the 2DEG mobility.
A Simple Parallel Conduction Extraction Method (SPCEM) for MODFETs and Undoped GaN-based HEMTs
We report a simple method to extract the mobility and sheet carrier densities of conduction channels in conventional modulation doped ﬁeld-effect transistor (MODFET) structures and unintentionally doped GaN-based high-electron mobility transistor (HEMT) structures for a special case. Extraction of the conduction channels from the magnetic ﬁeld-dependent data can present number of problems; even the most recent methods encounter great difﬁculties. For the GaN-based HEMT structures which have lower mobilities and larger effective masses than that of GaAs-based counterparts, these difﬁculties become more prominent. In this study, we describe a simple method for magnetotransport analysis to extract conduction channels successfully for a special case that is commonly encountered: one bulk channel and one two-dimensional electron gas (2DEG) channel. Advantage of this method is mainly its simplicity. The analysis can be done with only two magnetic ﬁeld-dependent measurements per temperature step. The method is applied to the magnetotransport results of an unintentionally doped AlGaN/AlN/GaN/AlN heterostructure over a temperature range of 29–350 K and in a magnetic ﬁeld range of 0–1.5 T (mBo1). The results are then compared with those obtained using a commercial package for these calculations namely: quantitative mobility spectrum analysis (QMSA).
Large Zero-Field Spin Splitting in AlGaN/AlN/GaN/AlN Heterostructures
This work describes Shubnikov–de Haas . SdH . measurements in Al 0.22 Ga 0.78 N / AlN / GaN / AlN heterostructures. Our experiments coupled with the analysis of the Hall data at various temperatures conﬁrm the formation of a two-dimensional electron gas . 2DEG . at the AlN/GaN interface. A beating pattern in the SdH oscillations is also observed and attributed to a zero-ﬁeld spin splitting of the 2DEG ﬁrst energy subband. The values of the effective spin-orbit coupling parameter and zero-ﬁeld spin-split energy are estimated and compared with those reported in the literature. We show that zero-ﬁeld spin-split energy tends to increase with increasing sheet electron density and that our value . 12.75 meV . is the largest one reported in the literature for GaN-based heterostructures.
DX-center Energy Calculation with Quantitative Mobility Spectrum Analysis in n-AlGaAs/GaAs Structures with Low Al Content
"If I have seen further it is by standing on the shoulders of giants." Sir Isaac Newton, Letter to Robert Hooke, February 5th, 1675