Z Tekeli

Publications (2)3.73 Total impact

• Article: Surface morphology of Al0.3Ga0.7N/Al2O3-high electron mobility transistor structure.

  S Cörekçi, D Usanmaz, Z Tekeli, M Cakmak, S Ozçelik, E Ozbay
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  ABSTRACT: We present surface properties of buffer films (AIN and GaN) and Al0.3Gao.zN/Al2O3-High Electron Mobility Transistor (HEMT) structures with/without AIN interlayer grown on High Temperature (HT)-AIN buffer/Al2O3 substrate and Al2O3 substrate. We have found that the GaN surface morphology is step-flow in character and the density of dislocations was about 10(8)-10(9) cm(-2). The AFM measurements also exhibited that the presence of atomic steps with large lateral step dimension and the surface of samples was smooth. The lateral step sizes are in the range of 100-250 nm. The typical rms values of HEMT structures were found as 0.27, 0.30, and 0.70 nm. HT-AIN buffer layer can have a significant impact on the surface morphology of Al0.3Ga0.7N/Al2O3-HEMT structures.
  Journal of Nanoscience and Nanotechnology 03/2008; 8(2):640-4. · 1.56 Impact Factor
• Source

  Available from: Suleyman Ozcelik

  Article: The behavior of the I-V-T characteristics of inhomogeneous (Ni/Au)–Al0.3Ga0.7N/AlN/GaN heterostructures at high temperatures

  Z. Tekeli, S. Altındal, M. Cakmak, S. Ozcelik, D. Calıskan, E. Ozbay
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  ABSTRACT: We investigated the behavior of the forward bias current-voltage-temperature (I‐V‐T) characteristics of inhomogeneous ( Ni / Au )– Al 0.3 Ga 0.7 N / Al N / Ga N heterostructures in the temperature range of 295–415  K . The experimental results show that all forward bias semilogarithmic I‐V curves for the different temperatures have a nearly common cross point at a certain bias voltage, even with finite series resistance. At this cross point, the sample current is temperature independent. We also found that the values of series resistance (R s ) that were obtained from Cheung’s method are strongly dependent on temperature and the values abnormally increased with increasing temperature. Moreover, the ideality factor (n) , zero-bias barrier height (Φ B0 ) obtained from I‐V curves, and R s were found to be strongly temperature dependent and while Φ B0 increases, n decreases with increasing temperature. Such behavior of Φ B0 and n is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of the barrier heights (BHs) at the metal/semiconductor interface. We attempted to draw a Φ B0 versus q/2kT plot in order to obtain evidence of the GD of BHs, and the values of Φ B0 =1.63  eV and σ 0 =0.217  V for the mean barrier height and sta- ndard deviation at a zero bias, respectively, were obtained from this plot. Therefore, a modified ln (I 0 /T²)-q²σ 0 ²/2(kT)² versus q/kT plot gives Φ B0 and Richardson constant A^* as 1.64  eV and 34.25  A / cm ²  K ² , respectively, without using the temperature coefficient of the barrier height. The Richardson constant value of 34.25  A / cm ²  K ² is very close to the theoretical value of 33.74  A / cm ²  K ² for undoped Al 0,3 Ga 0,7 N . Therefore, it has been concluded that the temperature dependence of the forward I‐V characteristics of the ( Ni / Au )– Al 0.3 Ga 0.7 / Al N / Ga N heterostructures can be successfully explained based on the thermionic emission mechanism with the GD of BHs.
  Journal of Applied Physics 10/2007; · 2.17 Impact Factor