Browsing by Author "Altindal, S."

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Open Access
The effect of insulator layer thickness on the main electrical parameters in (Ni/Au)/AlxGa1-xN/AIN/GaN heterostructures
(Wiley, 2010) Altindal, S.; Şafak, Y.; Taşçloǧlu I.; Özbay, Ekmel
(Ni/Au)Alx Ga1-x N/AlN/GaN(x = 0.22) heterostructures with and without a passivation layer of the SiNx were fabricated in order to see the effect of the insulator layer on the main electrical parameters such as zero-bias barrier height (BH) (φBO), ideality factor (n), series resistance (Rs) of the structure, and the interface state density (Nss). Some of these parameters were determined from both I-V and admittance (C-V and G/ω-V) measurements at room temperature and at 1 MHz and were compared. The experimental results show that the value of N ss in a Schottky contact without passivation is nearly 1 order of magnitude larger than that in a Schottky contact with SiNx passivation layers. Also, the values of Rs increase with the increasing thickness of the passivation layer. In the forward bias region, the negative values of capacitance are an attractive result of this study. This negative capacitance disappears in presence of the passivation layer. Copyright © 2010 John Wiley & Sons, Ltd.
Open Access
Electrical characterization of MS and MIS structures on AlGaN/AlN/GaN heterostructures
(ELSEVIER, 2010) Arslan, E.; Bütün, S.; Şafak, Y.; Uslu, H.; Tascioglu I.; Altindal, S.; Özbay, Ekmel
The forward and reverse bias I-V, C-V, and G/ω-V characteristics of (Ni/Au) Schottky barrier diodes (SBDs) on the Al 0.22Ga 0.78N/AlN/GaN high-electron-mobility-transistor (HEMTs) without and with SiN x insulator layer were measured at room temperature in order to investigate the effects of the insulator layer (SiN x) on the main electrical parameters such as the ideality factor (n), zero-bias barrier height ( B0), series resistance (R s), interface-state density (N ss). The energy density distribution profiles of the N ss were obtained from the forward bias I-V characteristics by taking into account the voltage dependence of the effective barrier height ( e) and ideality factor (n V) of devices. In addition, the N ss as a function of E c-E ss was determined from the low-high frequency capacitance methods. It was found that the values of N ss and R s in SBD HEMTs decreases with increasing insulator layer thickness.
Open Access
On the profile of frequency and voltage dependent interface states and series resistance in (Ni/Au)/Al0.22Ga0.78N/AlN/GaN heterostructures by using current-voltage (I-V) and admittance spectroscopy methods
(Elsevier, 2011-06-08) Demirezen, S.; Altindal, S.; Özelik, S.; Özbay, Ekmel
In order to explain the experimental effect of interface states (N ss) and series resistance (Rs) of device on the non-ideal electrical characteristics, current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/ω-V) characteristics of (Ni/Au)/Al 0.22Ga0.78N/AlN/GaN heterostructures were investigated at room temperature. Admittance measurements (C-V and G/ω-V) were carried out in frequency and bias voltage ranges of 2 kHz-2 MHz and (-5 V)-(+5 V), respectively. The voltage dependent Rs profile was determined from the I-V data. The increasing capacitance behavior with the decreasing frequency at low frequencies is a proof of the presence of interface states at metal/semiconductor (M/S) interface. At various bias voltages, the ac electrical conductivity (σac) is independent from frequencies up to 100 kHz, and above this frequency value it increases with the increasing frequency for each bias voltage. In addition, the high-frequency capacitance (C m) and conductance (Gm/ω) values measured under forward and reverse bias were corrected to minimize the effects of series resistance. The results indicate that the interfacial polarization can more easily occur at low frequencies. The distribution of Nss and R s is confirmed to have significant effect on non-ideal I-V, C-V and G/ω-V characteristics of (Ni/Au)/Al0.22Ga0.78N/AlN/ GaN heterostructures.
Open Access
Temperature dependent negative capacitance behavior in (Ni/Au)/AlGaN/AIN/GaN heterostructures
(Elsevier, 2010-02-10) Arslan, E.; Safak, Y.; Altindal, S.; Kelekci, O.; Özbay, Ekmel
The temperature dependent capacitance voltage (C-V) and conductance voltage (G/omega-V) characteristics of (Ni/Au)/Al(0.22)Ga(0.78)N/AlN/GaN heterostructures were investigated by considering the series resistance (R(s)) effect in the temperature range of 80-390 K. The experimental results show that the values of C and G/omega are strongly functioning of temperature and bias voltage. The values of C cross at a certain forward bias voltage point (similar to 2.8 V) and then change to negative values for each temperature, which is known as negative capacitance (NC) behavior. In order to explain the NC behavior, we drawn the C vs I and G/omega vs I plots for various temperatures at the same bias voltage. The negativity of the C decreases with increasing temperature at the forward bias voltage, and this decrement in the NC corresponds to the increment of the conductance. When the temperature was increased, the value of C decreased and the intersection point shifted towards the zero bias direction. This behavior of the C and G/omega values can be attributed to an increase in the polarization and the introduction of more carriers in the structure. R(s) values increase with increasing temperature. Such temperature dependence is in obvious disagreement with the negative temperature coefficient of R or G reported in the literature. The intersection behavior of C-V curves and the increase in R(s) with temperature can be explained by the lack of free charge carriers, especially at low temperatures.