T. 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.

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.

Pirani Vacuum Gauges Using Silicon-on-Glass and Dissolved-Wafer Processes for the Characterization of MEMS Vacuum Packaging

This paper presents the design and implementation of Pirani vacuum gauges for the characterization of vacuum packaging of microelectromechanical systems (MEMS). Various Pirani vacuum gauges are fabricated with two different standard in-house fabrication processes, namely the silicon-on-glass (SOG) process and dissolved-wafer process (DWP). The Pirani gauges utilize meander-shaped suspended silicon coils as the heaters and two isolated silicon islands in the close proximity of the heater that function as dual-heat sinks to enhance the sensitivity and dynamic range as compared to a microbridge with a single heat sink. The gauges are designed to occupy an area of 4 mm × 1.5 mm. The DWP Pirani gauge fabricated with a structural thickness of 14 mum and a gap of 2 mum shows a measured sensitivity of 4.2×10⁴ (K/W)/Torr in a dynamic range of 10-2000 mTorr. The SOG Pirani gauge fabricated with a structural thickness of 100 mum and a gap of 3 mum shows a lower measured sensitivity of 3.8×10³ (K/W)/Torr in a dynamic range of 50-5000 mTorr; however, the 100 mum-thick structural layer results in a much more robust process against stress-based deformations in suspended silicon compared to the DWP Pirani gauges. Each gauge is used to monitor the pressure of a different packaging approach. The DWP Pirani gauge is used to detect the pressure of a wafer-level vacuum package, where the pressure inside the cavity is measured to be about 2.4 mTorr. The SOG Pirani gauge is used the monitor the pressure inside a hybrid platform package which is vacuum-sealed using a projection welder, where the pressure is measured to be about 1400 mTorr. These measurements verify that the DWP and SOG Pirani gauges can be used for the characterization of wafer-level or hybrid platform vacuum packages for MEMS devices.

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.

The effect of humidity on electronic conductivity of an Au/CuO/Cu2O/Cu sandwich structure

In this study it was aimed to research the effect of humidity on the current-voltage characteristics and capacitance of an Au/CuO/Cu2 O/Cu sandwich structure. Cuprous oxide (Cu2 O) and cupric oxide (CuO) layers were grown on a copper sheet. In order to complete the fabrication of the Au/CuO/Cu2 O/Cu sandwich structure a gold metal contact was then applied on the cupric oxide layer under the pressure of 1 × 10-6 Torr. The current-voltage characteristics and effective capacitance of the sandwich structure were measured in various humidity ranges at a temperature 20 °C. It was observed that the electronic conduction and capacitance of the Au/CuO/Cu2 O/Cu structure were strongly dependent on humidity. The effect of humidity in Au/CuO/Cu2 O/Cu was discussed by means of the electric dipole moment of water.