Research Information System
Thesis Type: Doctorate
Institution Of The Thesis: Gazi Üniversitesi, Fen Bilimleri Enstitüsü, Turkey
Approval Date: 2012
Student: YASEMİN ŞAFAK ASAR
Supervisor: ŞEMSETTİN ALTINDAL
Open Archive Collection: AVESIS Open Access Collection
Abstract:The temperature dependent C −V and G/ω −V characteristics of (Ni/Au)/Al0.22Ga0.78N/AlN/GaN hetero-structures were investigated by considering the s R effect in the temperature range of 80390 K. The experimental results show that the values of C and G/ω are strongly functioning of temperature and bias voltage. The values of C cross at a certain forward bias voltage point (~2,8 V) and then change to negative values for each temperature, known as negative capacitance (NC) in the literature. In order to explain the NC behavior, we drawn the C vs I and G/ω 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. This behavior of the C and G/ω values can be attributed to an increase in the polarization and the introduction of more carriers in the structure. s R values increase with increasing temperature. The intersection behavior of C −V curves and the increase in Rs values with temperature can be explained by the lack of free charge carriers, especially at low temperatures. The surface states in Al0.22Ga0.78N/AlN/GaN heterostructures were investigated. C −V and G/ω −V measurements were carried out in the frequency range of 5 kHz to 1 MHz, and an equivalent circuit model was used to analyze the experimental data. The analysis of the frequency dependent capacitance and conductance data was performed, assuming models in which states are located at the metal GaN surface. The density ( ss N ) and time constant (τ ) of the surface states have been determined as a function of energy ( c ss E − E ). To compare the change in diode parameters in the presence of insulator layer between metal and GaN layers, with the thick of 5,5 nm SiNx layer was grown on GaN layer. Experimental results show that the presence of insulator layer decreases the leakage current, while the values of n ve B0 Φ increase. In addition, in the presence of insulator layer NC arise in higher values of forward bias voltages.