Dilber Esra Yıldız

Gaussian distribution of inhomogeneous barrier height in Al/SiO2/p-Si Schottky diodes

The forward and reverse bias current-voltage (I-V) characteristics of Al/SiO2/p-Si (metal-insulator-semiconductor) type Schottky diodes (SDs) were measured in the temperature range of 200–400 K. Evaluation of the experimental I-V data reveals a decrease in ΦB0 and Rs but an increase in n, with a decrease in temperature. To explain this behavior of ΦB0 with temperature, we have reported a modification which included n and the tunneling parameter αχ1/2δ in the expression of reverse saturation current I0. Thus, a corrected effective barrier height ΦB eff(I-V) vs T has a negative temperature coefficient (α≈−5×10−4 eV/K), and it is in good agreement with α=−4.73×10−4 eV/K of Si band gap. Such behavior of Rs estimated from Cheung’s method could be expected for semiconductors in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures. Also, there is a linear correlation between ΦB0(I-V) and n due to the inhomogeneities of the barrier heights (BHs). The conventi...

Analysis of temperature dependent current-conduction mechanisms in Au/TiO2/n-4H-SiC (metal/insulator/semiconductor) type Schottky barrier diodes

In order to determine the effective current-conduction mechanisms in Au/TiO2/n-4H-SiC (metal-insulator semiconductor) type Schottky barrier diodes (SBDs), their current-voltage (I-V) measurements were carried out in the temperature range of 200–380 K. Some electrical parameters, such as ideality factor (n), zero-bias barrier height (BH) (ΦBo), series and shunt resistances (Rs, Rsh), were obtained as 5.09, 0.81 eV, 37.43 Ω, and 435 kΩ at 200 K and 2.68, 0.95 eV, 5.99 Ω, and 73 kΩ at 380 K, respectively. The energy density distribution profile of surface states (Nss) was extracted from the forward-bias I-V data by taking into account voltage dependent of the ideality factor (nV), effective BH (Φe), and Rs for 200, 300, and 380 K. The Ln(I) vs V plots are completely parallel in the intermediate bias voltages, which may be well explained by field emission (FE) mechanism for each temperature. On the other hand, the high value of n cannot be explained with this mechanism. Therefore, to explain the change in BH ...

CO2 gas detection properties of a TIO2/Al2O3 heterostructure under UV light irradiation

Al/TiO2/p-Si and Al/TIO2/Al2O3/p-Si samples were prepared using the atomic layer deposition method (ALD) and their gas sensing properties were investigated. The electrical properties of the samples were studied using a two probe method in the temperature range 25–230 °C and at room temperature UV conditions. The TiO2/Al2O3 heterojunction sample exhibited an excellent gas sensing response to CO2 gas at room temperature and improved the effect of UV light irradiation. The results showed that heterostructures helped to improve the gas sensor properties, affected the sensing at room temperature and thus guided the design of photocatalysts. The TiO2/ Al2O3 heterojunction prepared using this method can be used as a material for semiconductor gas sensors detecting poisonous gases like CO2 at room temperature with high sensitivity and selectivity.

ALD TiO2 thin film as dielectric for Al/p-Si Schottky diode

Electrical analysis of Al/p-Si Schottky diode with titanium dioxide (TiO2) thin film was performed at room temperature. The forward and reverse bias current–voltage (I–V) characteristics of diode were studied. Using thermionic emission (TE) theory, the main electrical parameters of the Al/TiO2/p-Si Schottky diode such as ideality factor (n), zero bias barrier height (ϕBo) and series resistance (Rs) were estimated from forward bias I–V plots. At the same time, values of n, ϕBo and Rs were obtained from Cheung’s method. It was shown that electrical parameters obtained from TE theory and Cheung’s method exhibit close agreement with each other. The reverse-bias leakage current mechanism of Al/TiO2/p-Si Schottky barrier diodes was investigated. The I–V curves in the reverse direction are taken and interpreted via both Schottky and Poole–Frenkel effects. Schottky effect was found to be dominant in the reverse direction. In addition, the capacitance–voltage (C–V) and conductance–voltage (G/w–V) characteristics of diode were investigated at different frequencies (50–500 kHz). The frequency dependence of interface states density was obtained from the Hill–Coleman method and the voltage dependence of interface states density was obtained from the high–low frequency capacitance method.

The effect of ultraviolet irradiation on the ultra-thin HfO2 based CO gas sensor

In this work, an effort has been made to fabricate ultrathin HfO2/Al2O3 sample by atomic layer deposition method for the fast detection of CO gas at room temperature. The effect of the operating temperature and the UV light on the gas sensing characteristics has been studied. We investigated the optimum operating temperature for the sample by sensing 25 ppm CO and CO2 gases from room temperature to 150 °C for 10 °C steps. The maximum response was obtained at 150 °C for both gases in the measurement temperature range. Also, the photoresponse measurements clearly show the effect of UV light on the sample. At room temperature, sensor showed superior response (14%) for 5 ppm CO gas. The response time of sensor is 6 s to 5 ppm CO gas concentration. The ultrathin HfO2 based sample shows acceptable gas sensitivity for 5 ppm CO gas at room temperature under UV light irradiation.

The Main Electrical and Interfacial Properties of Benzotriazole and Fluorene Based Organic Devices

Electrical and interfacial properties of ITO/PEDOT:PSS/poly((9,9-dioctylfluorene)-2,7-diyl(2-dodecyl-benzo[1,2,3]triazole)) (PFTBT)/Au devices were investigated using current-voltage (I-V), capacitance-voltage (C-V) and conductance-voltage (G/w-V) measurements at room temperature. The forward and reverse C-V and G/w-V measurements were carried out in the frequency range of 10 kHz-1MHz. The electrical parameters, barrier height (ΦBo ) and ideality factor (n) obtained from the forward bias LnI-V plot were found as 0.711 eV and 3.8, respectively. In addition, the series resistance (Rs ) was obtained using Norde and Cheungs methods; Rs were found as 19.052kΩ and 19.267kΩ, respectively. The experimental C-V and G/w-V characteristics of these structures at various gate biases show fairly large frequency dispersion especially at low frequencies and applied voltage due to interface states (Nss) in equilibrium with the conjugated copolymer, interfacial polymer and Rs . These observations indicate that at low frequencies, the charges at interface states can easily follow an AC signal and yield an excess capacitance and conductance. On the other hand, the values of Nss were determined using high-low frequency capacitance (CLF -CHF ) method and Nss are of order 1011 eV-1 cm−2 which is closer to the values obtained by Hill-Coleman method. Experimental results show that both Nss and Rs values should be taken into account in determining frequency and voltage dependent I-V, C-V and G/w-V characteristics for an organic structure.

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.

Frequency Dependent Dielectric Properties of ZnSe/p-Si Diode

The study on electrical and dielectric properties of the ZnSe/p-Si diode have been investigated using admittance measurements in the frequency range of 50 kHz - 1 MHz at room temperature. The experimental values of dielectric constant and dielectric loss are found in decreasing behavior with increase in frequency due to the characteristics of the interface capacitance in the diode and so that the similar behavior was observed in loss tangent. With the contribution of the series resistance, the results of the electrical conductivity analysis indicated direct proportionality to the frequency change. Additionally, electric modulus was discussed to represent the dielectric relaxation process in the diode structure.

ELECTRICAL PROPERTIES OF Al/p-Si STRUCTURE WITH Al2O3 THIN FILM FABRICATED BY ATOMIC LAYER DEPOSITION SYSTEM

Al2O3 insulator layer was deposited by atomic layer deposition (ALD) technique on p-type Si 〈111〉 and the Al/Al2O3/p-Si metal/insulator/semiconductor (MIS) structures were fabricated. The current–voltage (I−V) characteristics of these structures were investigated in two different temperatures. The main electrical parameters such as the ideality factor (n), zero bias barrier height (ΦBo(I−V)), and series resistance (Rs) values were found for 300 and 400K. The energy density distribution profiles of the interface state density (Nss) were determined from the I−V characteristics. In addition, the capacitance–voltage (C−V) and conductance–voltage (G/w−V) characteristics of devices were investigated in the frequency range 50–1000kHz at room temperature. Frequency-dependent electrical characteristics such as doping acceptor concentration (NA), energy difference between the valance band edge and bulk Fermi level (EF), diffusion potential (VD), barrier height (ΦB(C−V)), the image force barrier lowering (ΔΦB), maximum electric field (Em), and Rs values were determined using C−V and G/w−V plots. In addition, the Nss values were performed using Hill–Coleman method. According to experimental results, the locations of Nss and Rs have an important effect on I−V, C−V and G/w−V plots of MIS structure.