Ç. Erçelebi

The effect of substrate and post-annealing temperature on the structural and optical properties of polycrystalline InSe thin films

Abstract X-ray diffraction, scanning electron microscopy, compositional analysis and transmission measurements are performed on InSe thin films grown by thermal evaporation at different substrate and annealing temperatures of 150–250°C and 100–200°C, respectively. An analysis of structural measurements indicates that there exist three phases of In–Se system like InSe, In2Se3 and In6Se7 in the same film at low-substrate temperature, but at high-substrate temperatures, In2Se3 phase was absent. The composition of InSe films changed significantly with substrate temperature and slightly with annealing temperature because of re-evaporation of selenium. The transmission measurements were carried out at room temperature over the spectral range 0.5 to 2.5 μm. As a result of optical energy gap studies, the direct energy band gap was found to be in between 1.21 and 1.38 eV depending on substrate and annealing temperatures.

Electrical characterization of vacuum-deposited n-CdS/p-CdTe heterojunction devices

The effects of post-deposition processes such as dip and/or annealing in air on the material and device properties of vacuum-evaporated Au-CdTe/CdS-TO heterojunction solar cells have been investigated. The dip followed by air annealing at for 5 min improved the device efficiency significantly, resulting in decreased CdTe resistivity and enhanced grain size. The temperature-dependent current - voltage analysis indicated that above 280 K interface recombination dominates the current transport mechanism for the as-grown samples, while depletion region recombination starts to be dominant after annealing the samples with . Below 280 K multistep tunnelling is identified to be the dominant transport mechanism. Frequency-dependent capacitance - voltage studies revealed that after annealing with the density of interface states decreases and the quality of the heterointerface improves. The capacitance of the CdS/CdTe heterojunctions has been analysed using a model based on the existence of a single dominant trap level, identified at 0.40 eV above the valence band with a concentration of .

Structural and Electrical Properties of Cd Doped InSe Thin Films

Polycrystalline Cd doped InSe thin films were obtained by thermal co-evaporation of alpha-In2Se3 lumps and Cd onto glass substrates at a temperature of 150°C. The films were annealed at 150°C and 200°C. The films were found to contain around 46% In, 47% Se and 7% Cd in weight. The films exhibited p-type conductivity. The results of conductivity measurements have revealed that thermionic emission and variable range hopping are the two dominant conduction mechanisms, in the temperature ranges of 320-160 K and 150-40 K respectively. It was observed that above 240 K mobility is limited by the scattering at the grain boundaries. As the temperature decreases, thermal lattice scattering followed by the ionized impurity scattering dominate as the two main mechanisms controlling the mobility. Acceptor to donor concentration ratio was found to be slightly increasing due to annealing.

Electronic properties of polypyrrole/polyindene composite/metal junctions

Abstract Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, AI and In have been investigated. Rectifying junctions were observed for low work function metals, In and AI; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.

Growth and characterization of polycrystalline InSe thin films

Abstract Indium selenide films were obtained by the thermal evaporation of undoped crystals at substrate temperatures of 210 and 300 °C. Films were found to exhibit n-type conductivity. Scanning electron microscopy established that the films grown on glass substrates held at 210 °C had an atomic content of In 46.66 Se 53.34 , whereas the films obtained under the same conditions and annealed in vacuum at 150 °C had an atomic content of In 48.13 Se 51.87 . X-Ray diffraction indicated that the films were polycrystalline in nature and crystallized in the D 1 3h space group. From an analysis of Hall and conductivity measurements, performed in the temperature ranges 110–320 K and 10–320 K respectively, thermionic emission is considered to be the predominant transport mechanism above 200 K. The current transport below 75 K is due to the hopping of carriers between localized states. In the intermediate temperature region, both thermally assisted tunnelling and thermionic emission contribute to the conduction.

Investigation of photovoltaic properties of amorphous InSe thin film based Schottky devices

In this study, device behavior of amorphous InSe thin films was investigated through I–V, C–V and spectral response measurements onto SnO2/p-InSe/metal Schottky diode structures. Various metal contacts such as Ag, Au, Al, In and C were deposited onto amorphous p-InSe films by the thermal evaporation technique. The best rectifying contact was obtained in a SnO2/p-InSe/Ag Schottky structure from I–V measurements, while the Au contact had poor rectification. Other metal contacts (Al, In and C) showed almost ohmic non-rectifying behaviors for all samples. The ideality factor and barrier height values with the Ag contact were found to be 2 and 0.7 eV, respectively.

Studies on device properties of an n-AgIn5Se8/p-Si heterojunction diode

In this study, polycrystalline thin films of ternary AgIn5Se8 compounds with n-type conductivity were deposited on p-type Si substrates from the powder of a Ag3In5Se9 single crystal by a thermal evaporation technique. Transport and photo-transport properties of the In/n-AgIn5Se8/p-Si/Al sandwich structure were investigated by analyzing temperature-dependent dc current–voltage (I–V), and photo-response measurements carried out in the temperature range of 200–360 K. In order to obtain the series resistance (Rs) and shunt resistance (Rsh) values, the parasitic resistance (Rp = ∂V/∂I) was analyzed for forward and reverse voltages. Devices showed very good diode behavior with the rectification factor of about 104 at 1.0 V in dark. The ideality factor n and the barrier height b values of the heterojunction diode were determined by performing different I–V plots. A space charge limited current method was used to determine the conduction mechanism at a high bias region. Spectral photo-response analyses showed a shifting of the band edge to the lower energies with increasing temperature.

Structural and electrical characterization of Ag3Ga5Te9 and Ag3In5Se9 crystals

X-ray powder diffraction studies revealed that Ag 3 Ga 5 Te 9 and Ag 3 In 5 Se 9 crystallize in orthorhombic and tetragonal systems, respectively. The temperature dependent conductivity and Hall effect measurements have been carried out between 65-480 K. Ag 3 Ga 5 Te 9 exhibits p-type conduction with a room temperature conductivity of 4.3 × 10 -4 (Ω. cm) -1 and mobility less than 1 cm 2 /V S. Ag 3 In 5 Se 9 was identified to be n-type with room temperature conductivity 7.2 × 10 -5 (Ω. cm) -1 and mobility 20 cm 2 /V. s. From temperature dependence of the conductivity three different impurity ionization energies were obtained for both compounds. The anomalous behavior observed in the temperature dependence of mobility was attributed to the different features of the microstructure.

Growth, electrical and structural characterization of β-GaSe thin films

GaSe thin films were deposited onto the glass substrates kept at 200° and 300°C by the thermal evaporation of GaSe crystals under the pressure of 10−5 Torr. X-ray analysis of the films revealed that films grown at 200°C are amorphous in nature while the films grown at 300°C are polycrystalline β-GaSe. The temperature dependent electrical conductivity measurements in the region of 320–100 K for the films grown at 300°C showed that the transport mechanisms are the thermionic emission of charged carriers and the variable range hopping above and below 180 K, respectively. Space charge limited current (SCLC) studies have also been performed on these films through the current-voltage measurements at different temperatures and a dominant hole trap at 0.233 eV from the top of the valance band with a trap density of ∼1.6 × 1011 cm−3 is identified.

Characterization of p-In2Se3 thin films

Indium selenide thin films were deposited onto glass substrates kept at 150 °C by thermal evaporation of α-In2Se3. Some of the films were annealed at 150 °C and 200 °C and they all were found to exhibit p-type conductivity without intentional doping. Scanning electron microscopy (SEM) established that the films have an atomic content of In51Se49. X-ray diffraction (XRD) indicated that the as-grown films were amorphous in nature and became polycrystalline β-In2Se3 films after annealing. The analysis of conductivity temperature-dependence measurements in the range 320–100 K revealed that thermal excitation and thermionic emission of the carriers are the predominant conduction mechanisms above 200 K in the amorphous and polycrystalline samples, respectively. The carrier transport below 200 K is due to variable range hopping in all the samples. Hall measurements revealed that the mobility of the polycrystalline films is limited by the scattering of the charged carriers through the grain boundaries above 200 K.