Necmi Serin

Annealing effects on the properties of copper oxide thin films prepared by chemical deposition

We have investigated the annealing effect on the structural, optical and electrical properties of copper oxide films prepared on glass substrates by chemical deposition. The films were annealed in air for different temperatures ranging from 200 to 350 °C. X-ray diffraction patterns showed that the films as-deposited and annealed at 200 and 250 °C are of cuprite structure with composition Cu2O. Annealing at 300 °C converts these films to CuO. This conversion is accompanied by a shift in the optical band gap from 2.20 eV to 1.35 eV. Also this conversion was obtained by the dc electrical conductivity and FTIR spectroscopy measurements.

The double Gaussian distribution of barrier heights in Al/TiO2/p-Si (metal-insulator-semiconductor) structures at low temperatures

The current-voltage (I-V) characteristics of Al/TiO2/p-Si metal-insulator-semiconductor (MIS) structures have been investigated in the temperature range of 80–300 K. An abnormal decrease in the zero bias barrier height (BH) (ϕb0) and an increase in the ideality factor (n) with decreasing temperature have been explained on the basis of the thermionic emission (TE) theory with Gaussian distribution (GD) of the BHs due to the BH inhomogeneities. The temperature dependence of the experimental I-V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double GD with mean BH values (ϕ¯b0) of 1.089 and 0.622 eV and standard deviations σs of 0.137 and 0.075 V, respectively. Thus, the modified ln(I0/T2)−q2σ02/2(kT)2 versus q/kT plot gives ϕ¯b0 values and Richardson constants (A∗) as 1.108 and 0.634 eV and 31.42 and 23.83 A/cm2 K2, respectively, without using the temperature coefficient of the BH. The value of the effective Richardson constant of 31.42 A/cm2 K2 is very close to the theoretical va...

The influence of series resistance and interface states on intersecting behavior of I–V characteristics of Al/TiO2/p-Si (MIS) structures at low temperatures

In this study, we have investigated the intersection behavior of the forward bias current–voltage (I–V) characteristics of the Al/TiO2/p-Si (MIS) structures in the temperature range of 100–300 K. The intersection behavior of the I–V curves appears as an abnormality when compared to the conventional behavior of ideal Schottky diodes and MIS structures. This behavior is attributed to the lack of free charge at a low temperature and in the temperature region, where there is no carrier freezing out, which is non-negligible at low temperatures, in particular. The values calculated from the temperature-dependent forward bias I–V data exhibit unusual behavior, where the zero-bias barrier height (b0) and the series resistance (Rs) increase with increasing temperature. Such temperature dependence of b0 and Rs is in obvious disagreement with the reported negative temperature coefficient. An apparent increase in the ideality factor (n) and a decrease in the b0 at low temperatures can be attributed to the inhomogeneities of the barrier height, the thickness of the insulator layer and non-uniformity of the interfacial charges. The temperature dependence of the experimental I–V data of the Al/TiO2/p-Si (MIS) structures has revealed the existence of a double Gaussian distribution with mean barrier height values () of 1.108 eV and 0.649 eV, and standard deviations (σs) of 0.137 V and 0.077 V, respectively. Furthermore, the temperature dependence of the energy distribution of interface state density (Nss) profiles has been determined from forward bias I–V measurements by taking into account the bias dependence of the effective barrier height (e) and n. The fact that the values of Nss increase with increasing temperature has been attributed to the molecular restructuring and reordering at the metal/semiconductor interface under the effect of temperature.

Electrical characteristics of DNA-based metal-insulator-semiconductor structures

High quality sandwich device was fabricated from wheat DNA molecular film by solution processing located between Au and n-type silicon inorganic semiconductor. We have performed the electrical characteristics of the device such as current–voltage (I–V) and capacitance–voltage (C–V) at room temperature. DNA-based on this structure showed an excellent rectifying behavior with a typical ideality factor of 1.22, and that DNA film increased the effective barrier height by influencing the space charge region of Si. We proposed that DNA could be an insulatorlike material with a wide optical band energy gap of 4.19 eV from its optical absorbance characteristics. Additionally, the energy distribution of interface state density, determined from the forward bias I–V characteristics by taking into account the bias dependence of the effective barrier height, decreases exponentially with bias from 7.48×1015 m−2 eV−1 in (Ec−0.40) eV to 8.56×1014 m−2 eV−1 in (Ec−0.72) eV.

Crossover from Nearest-Neighbor Hopping Conduction to Efros–Shklovskii Variable-Range Hopping Conduction in Hydrogenated Amorphous Silicon Films

We presented the results of optical and electrical studies of the properties of hydrogenated amorphous silicon (a-Si:H) film which was prepared by hot wire method. Using transmittance measurements, the dielectric constant of the a-Si:H was determined. The temperature-dependent conductivity was measured using the two-point probe method in the temperature range 115–326 K. It was shown that the temperature-dependent conductivity can be well explained by the nearest-neighbor hopping conduction and the Efros–Shklovskii variable-range hopping conduction models. A clear transition from the nearest-neighbor hopping conduction mechanism to the Efros–Shklovskii variable-range hopping conduction mechanism was also observed. The transition between two conduction regimes and characteristic hopping temperatures, as well as the complete set of parameters describing the properties of the localized electrons (the localization length, the hopping energy, the hopping distance, the width of the Coulomb gap, and the value of the density of states at the Fermi level) were determined.

The effects of film thickness on the optical properties of TiO2?SnO2 compound thin films

In this work, TiO2?SnO2 compound thin films was synthesized by the sol?gel technique, and the effects of film thickness on the optical and structural properties of these thin films were investigated. Optical constants such as the refractive index, extinction coefficient, dielectric constant and third-order optical nonlinear susceptibility were determined from the measured transmittance spectra in the wavelength range 300?1500?nm using the envelope method. Meanwhile, the dispersion behavior of the refractive index was studied in terms of the single-oscillator Wemple?DiDomenico (W?D) model, and the physical parameters of the refractive index dispersion parameter and the dispersion energy were found. Furthermore, the optical band gap values were calculated by the W?D model and the Tauc model, respectively. It is observed that the values obtained from the W?D model are in quite good agreement with those determined from the Tauc model. Important changes in optical and dielectric constants were observed by means of variation in film thickness. To examine the structure of the thin films, x-ray diffraction (XRD) methods were used. Combined with XRD analysis, the observed variations in both the refractive index and optical band gap are directly correlated with the structural evolution of the composite TiO2?SnO2 thin films. The most significant results of the present study are that the thickness of the film can be used to modify the optical, structural and dielectric properties of TiO2?SnO2 thin films.

Improved conductivity of Sb-doped SnO2 thin films

Sb-doped SnO2 thin films at different thickness have been grown by sol-gel dip-coating method. All of the films exhibit degenerate semiconductor behavior and high free carrier concentrations. In the films, electrical transport can be explained reasonably well by assuming the electron-electron interactions (EEIs) contribution to the measured electrical conductivity. Our experimental observations are consistent with the theoretical description of the EEI. The effect of films thickness on the EEI contribution is also discussed. When the thickness of film reaches to 1550 nm, the agreement between the EEI theory and experimental data becomes unsatisfactory.

Electrical conduction properties of In-doped ZnO thin films

The electrical conduction mechanism of undoped and In-doped ZnO thin films is investigated. The behavior of conductivity is consistent with the variable-range hopping conduction mechanism. From the experimental data, the values of the density of states at the Fermi level, the hopping distance and the average hopping energy are obtained. The effect of these parameters on In doping level is discussed. It was found that the value of the density of states at the Fermi level increases with increasing In doping level, which is the reason for the rise in conductivity of the films.

Current flow mechanism in Cu2O/p-Si heterojunction prepared by chemical method

Cu2O thin films were chemically deposited on single-crystal p-Si substrates to form Cu2O/p-Si heterojunctions. The structure of the Cu2O films was analysed by x-ray diffraction spectroscopy and UV–Vis–NIR transmittance spectra. In order to investigate the dark current transport mechanism in Cu2O/p-Si heterojunctions the current–voltage characteristics were measured in the temperature range 120–320 K and capacitance–voltage characteristics at a high frequency of ~1 MHz at room temperature. The I–V–T characteristics revealed that the forward current was determined by trap-assisted multi-step tunnelling. The activation energy determined from the saturation current and the junction built-in potential determined from the capacitance–voltage characteristics were about 0.18 eV and 1.10 V at room temperature, respectively.

Influence of annealing temperature on structural, morphological and optical properties of nanostructured TiO2 thin films

Abstract Thermal annealing is widely used to improve crystal quality, which affects electrical and structural properties by reducing study defects in materials. Therefore, enormous research efforts were focused on the control of material surface nanostructure through annealing processes, which is of interest for various technologies. However, no work providing a detailed explanation for the structural, morphological and optical parameters of nanostructured TiO2 thin films deposited on glass at temperature above 500°C by the sol–gel dip coating method has been presented to date. In this work, we have grown nanostructured TiO2 thin films by sol–gel dip coating method on glass substrates at room temperature and studied the effects of annealing temperature from 200 to 700°C on optical performance, microstructural changes and surface morphology evolution. The results of this work may be summarised as follows: the X-ray diffraction results show that annealed TiO2 thin films have anatase crystal structure, and the intensities of the peaks of the crystalline phase increased with the increase in annealing temperature; from atomic force microscopy images, distinct variations in morphology of the thin films were also observed; and optical results show that TiO2 films exhibit high visible transmittance, and it has a maximum transmittance of ∼93·61% at 500°C annealing temperature. The optical band gap of the as grown thin films decreases from 3·68 to 3·31 eV with the increase in annealing temperatures. The TiO2 thin film annealed at 500°C has the best optical property. The change in structural, morphological and optical properties with annealing temperature demonstrates that this material has a potential to be used as a novel technology such as nanoelectronics and possibly nano-optoelectronic devices based on nanomaterial for insulating, semiconducting and electron and/or hole blocking layer, etc.