Mert Yıldırım

Analyses of temperature-dependent interface states, series resistances, and AC electrical conductivities of Al/p?Si and Al/Bi4Ti3O12/p?Si structures by using the admittance spectroscopy method

In this study, Al/p—Si and Al/Bi4Ti3O12/p—Si structures are fabricated and their interface states (Nss), the values of series resistance (Rs), and AC electrical conductivity (σac) are obtained each as a function of temperature using admittance spectroscopy method which includes capacitance—voltage (C—V) and conductance—voltage (G—V) measurements. In addition, the effect of interfacial Bi4Ti3O12 (BTO) layer on the performance of the structure is investigated. The voltage-dependent profiles of Nss and Rs are obtained from the high-low frequency capacitance method and the Nicollian method, respectively. Experimental results show that Nss and Rs, as strong functions of temperature and applied bias voltage, each exhibit a peak, whose position shifts towards the reverse bias region, in the depletion region. Such a peak behavior is attributed to the particular distribution of Nss and the reordering and restructuring of Nss under the effect of temperature. The values of activation energy (Ea), obtained from the slope of the Arrhenius plot, of both structures are obtained to be bias voltage-independent, and the Ea of the metal-ferroelectric-semiconductor (MFS) structure is found to be half that of the metal—semiconductor (MS) structure. Furthermore, other main electrical parameters, such as carrier concentration of acceptor atoms (NA), built-in potential (Vbi), Fermi energy (EF), image force barrier lowering (Δ Φb), and barrier height (Φb), are extracted using reverse bias C−2—V characteristics as a function of temperature.

Influence of interfacial layer thickness on frequency dependent dielectric properties and electrical conductivity in Al/Bi4Ti3O12/p-Si structures

Three Al/Bi4Ti3O12/p-Si structures were fabricated with different interfacial layer thickness values (10, 25, and 53 nm) and admittance measurements of the structures were carried out between 1 kHz and 1 MHz in order to investigate the influence of interfacial layer thickness on dielectric properties of these structures. For the structure with thicker interfacial layer, higher dielectric constant (e′) and dielectric loss (e″) values were obtained at low frequencies. At high frequencies, these parameters tend to be saturated and become almost constant. Loss tangent versus frequency plots exhibit a peak and magnitude of the peak weakens with increasing frequency and shifts toward high frequency region. The dispersion in e′ and e″ with varying thickness at low frequencies was ascribed to interfacial polarization. In addition, obtained e″ values indicated higher energy dissipation in the structure with thicker interfacial layer. Admittance data of the structures were also considered in terms of modulus formal...

Investigation on dielectric properties of atomic layer deposited Al2O3 dielectric films

Al/Al2O3/p-Si Schottky barrier diodes (SBDs) were fabricated using atomic layer deposition technique in order to investigate dielectric properties of SBDs. For this purpose, admittance measurements were conducted at room temperature between −1 V and 3 V in the frequency range of 10 kHz and 1 MHz. In addition to the investigation of Al2O3 morphology using atomic force microscope, dielectric parameters; such as dielectric constant (e′), dielectric loss (e″), dielectric loss tangent (tan δ), and real and imaginary parts of dielectric modulus (M′ and M″, respectively), were calculated and effect of frequency on these parameters of Al/Al2O3/p-Si SBDs was discussed. Variations in these parameters at low frequencies were associated with the effect of interface states in low frequency region. Besides dielectric parameters, ac electrical conductivity of these SBDs was also investigated.

The effects of Bi4Ti3O12 interfacial ferroelectric layer on the dielectric properties of Au/n-Si structures

Au/n-Si metal-semiconductor (MS) and Au/Bi4Ti3O12/n-Si metal-ferroelectric-semiconductor (MFS) structures were fabricated and admittance measurements were held between 5 kHz and 1 MHz at room temperature so that dielectric properties of these structures could be investigated. The ferroelectric interfacial layer Bi4Ti3O12 decreased the polarization voltage by providing permanent dipoles at metal/semiconductor interface. Depending on different mechanisms, dispersion behavior was observed in dielectric constant, dielectric loss and loss tangent versus bias voltage plots of both MS and MFS structures. The real and imaginary parts of complex modulus of MFS structure take smaller values than those of MS structure, because permanent dipoles in ferroelectric layer cause a large spontaneous polarization mechanism. While the dispersion in AC conductivity versus frequency plots of MS structure was observed at high frequencies, for MFS structure it was observed at lower frequencies.

Effects of Frequency and Bias Voltage on Dielectric Properties and Electric Modulus of Au/Bi4Ti3O12/n-Si (MFS) Capacitors

In this work, a metal-ferroelectric-semiconductor (MFS) type capacitor was fabricated and admittance measurements were held in a wide frequency range of 1 kHz-5 MHz at room temperature for the investigation of frequency and voltage dependence of complex dielectric constant, complex electric modulus and electrical conductivity of the MFS capacitor . Bismuth titanate (Bi 4 Ti 3 O 12 ) with high dielectric constant was used as interfacial ferroelectric material and the structure of MFS capacitor was obtained as Au/Bi 4 Ti 3 O 12 /n-Si. Experimental results showed that dielectric, modulus and conductivity parameters are strong functions of frequency and voltage especially in depletion and accumulation regions due to the existence of surface states (N ss ), series resistance (R s ), interfacial polarization and interfacial layer. It was found that R s of the structure and interfacial ferroelectric layer are efective in accumulation region whereas surface states (N ss ) and interfacial polarization are efective in depletion region. Also the changes in dielectric, modulus and conductivity parameters become considerably high particularly at low frequencies due to high values of R s and N ss . The observed anomalous peak in voltage dependent plots of capacitance and dielectric constant was atributed to the particular density distribution of N ss , R s and minority carrier injection. Moreover, the value of conductivity at low and intermediate frequencies is almost independent of frequency thus low frequency data was used to extract d.c. conductivity. This work showed that the use of high-dielectric Bi 4 Ti 3 O 12 as ferroelectric interfacial layer in a MFS capacitor is preferable due to high values of its dielectric constant compared with traditional insulator layer materials such as SiO 2 and SnO 2 . Therefore, a MFS capacitor with Bi 4 Ti 3 O 12 interfacial layer can store more energy thanks to its high dielectric constant.