Dark Resistivity Research Articles

The influence of hydrazine hydrate on the photoconductivity of PbS thin film

High quality poly crystalline nanostructured PbS thin film has been deposited on a glass substrate by chemical deposition technique. The hydrazine hydrate as a reducing agent for lead ion has been used for preparation of the film. After deposition, the film has been annealed, and then the influence of hydrazine hydrate on the dark resistivity and photosensitivity of film have been investigated. It was found that in the presence of hydrazine hydrate in chemical deposition bath, the resistance of the prepared film increases to mega ohm. The measured room temperature detectivity of the film is 4 × 10 9 W −1 Hz 1/2 cm at the wavelength of 2.4 μm. The experimental results have shown that the PbS film, which has been prepared according to this procedure, can be applied as an infrared detector in the range of 1.0–3.0 μm.

Fibrous nanorod network of bismuth oxide by chemical method

Fibrous nanorod network of monoclinic Bi 2O 3 was grown onto amorphous glass substrates at room temperature using a simple and soft chemical method from aqueous bismuth nitrate solution. The fibrous network of nanorods was characterized by morphological, structural, optical and electrical properties. The nanorods were nearly uniform in dimensions, with diameter around 40 nm and length ∼500 nm. The optical properties of the nanorods are studied in the UV–vis spectral range. The band gap calculated from the absorption spectrum is found to be 3.1 eV, indicating a considerable “blue shift” relative to the bulk material. The dark electrical resistivity was measured as a function of temperature, which revealed the semiconducting nature with high electrical resistivity of the order of 10 7 Ω cm.

Simulation, modeling, and crystal growth of Cd0.9Zn0.1Te for nuclear spectrometers

High-quality, large (10 cm long and 2.5 cm diameter), nuclear spectrometer grade Cd0.9Zn0.1Te (CZT) single crystals have been grown by a controlled vertical Bridgman technique using in-house zone refined precursor materials (Cd, Zn, and Te). A state-of-the-art computer model, multizone adaptive scheme for transport and phase-change processes (MASTRAP), is used to model heat and mass transfer in the Bridgman growth system and to predict the stress distribution in the as-grown CZT crystal and optimize the thermal profile. The model accounts for heat transfer in the multiphase system, convection in the melt, and interface dynamics. The grown semi-insulating (SI) CZT crystals have demonstrated promising results for high-resolution room-temperature radiation detectors due to their high dark resistivity (ρ≈2.8 × 1011 Θ cm), good charge-transport properties [electron and hole mobility-life-time product, μτe≈(2–5)×10−3 and μτh≈(3–5)×10−5 respectively, and low cost of production. Spectroscopic ellipsometry and optical transmission measurements were carried out on the grown CZT crystals using two-modulator generalized ellipsometry (2-MGE). The refractive index n and extinction coefficient k were determined by mathematically eliminating the ∼3-nm surface roughness layer. Nuclear detection measurements on the single-element CZT detectors with 241Am and 137Cs clearly detected 59.6 and 662 keV energies with energy resolution (FWHM) of 2.4 keV (4.0%) and 9.2 keV (1.4%), respectively.

Detectivity studies of SMD-packaged ZnSSe and ZnMgS UV detectors

The 1/f noise and shot noise studies were carried out on molecular beam epitaxy (MBE)-grown ZnS0.85Se0.15 and Zn0.43Mg0.57S ultraviolet (UV) detectors packaged in surface mount lead frames. Three ZnS0.85Se0.15 detectors with different thicknesses of the active layer and the top electrode pad were used. The highest onset of reverse bias for the appearance of 1/f noise is −27.5 V, and the highest dark resistances at zero bias is R0=3.7×1013 Θ. The observed difference in their noise performance implies that the increase of the thicknesses of both the active layer and the top electrode pad can significantly lower the noise levels and in turn lead to higher detectivity. The best detectivity achieved is 8.75×1013 cm Hz1/2 W−1 in a ZnS0.85Se0.15 detector with an active layer of 5000 A and a top electrode pad of Cr (50 A)/Au (8000 A). The typical detectivity achieved on Zn0.43Mg0.57S devices that have an active layer thickness just exceeds the critical thickness of phase transition is 1.54×1012 cm Hz1/2 W−1.

Characterization of CuInS 2 thin films prepared by ion layer gas reaction method

Ion layer gas reaction (ILGAR) method for CuInS 2 films was developed by using ethanol as solvent. The influences of [Cu] / [In] ratio in ethanol solution on structural, chemical, topographical, optical and electrical properties of CuInS 2 thin films were investigated. X-ray diffraction and X-ray photoelectron spectroscopy results showed that all CuInS 2 thin films derived from different [Cu] / [In] ratios were sphalerite with preferred orientation (112). Scanning electron microscopy revealed that the microstructure and the growth rate of the films depended on the relative amounts of copper in the solution. When [Cu] / [In] ratio was 1.50 growth rate of the film was about 30 nm/cycle and the film was uniform, compact and good in adhesion to the substrates. The absorption coefficients of CuInS 2 films estimated from transmittance spectra were more than 10 4 cm − 1 , and the films behaved with p-type conductivity. The band gap E g changed from 1.30 to 1.40 eV and the dark resistivity decreased from 3.1 to 0.04 Ω cm with increase of [Cu] / [In] ratio.

Fabrication and characterization of sputtered titanium dioxide films

TiO 2 thin films were prepared under various conditions by using a reactive RF sputtering technique. The structural, optical and electrical characteristics of the films have been investigated. All as-deposited films were amorphous. After annealing at T > 673 K, the crystallinity of the observed tetragonal anatase phase appeared improved. The optical band gap, determined by using Tauc plot, has been found to amount to 3.38 ± 0.03 and 3.21 ± 0.03 eV for the direct and indirect transition, respectively. Also the complex optical constants for the wavelength range 300–2500 nm are reported. Using the two-point probe technique, the dark resistivity has been measured as a function of the film thickness, d. The resistivity, ρ, of the samples has been found to decrease markedly with increasing thickness, but only for d < 100 nm. The behaviour of ρd versus d was found to fit properly with the Fuchs and Sondheimer relation with parameters ρ o = 4.95 × 10 6 Ω cm and mean free path, l = 310 ± 2 nm. The log ρ versus 1/ T curves show three distinct regions with values for the activation energy of 0.03 ± 0.01, 0.17 ± 0.01 and 0.50 ± 0.02 eV, respectively.

Layered Compound Semiconductor GaSe and GaTe Crystals for THz Applications

AbstractThe single crystal growth of layered semiconductors GaSe and GaTe by vertical Bridgman technique using zone refined selenium (Se), tellurium (Te) and high purity (HP) gallium (Ga) have been described. The grown crystals (2.5 cm diameter and ∼10 cm long) have demonstrated efficient broadband tunable THz emission and as sensitive THz detectors. The crystals have shown promising characteristics with good optical quality, high dark resistivity, wide band gap (GaSe-2.01 eV and GaTe-1.66 eV at 300 K), good anisotropic (parallel, p &amp; perpendicular, pa) electrical properties (σ∥ vs σ⊥ and μ∥ vs σ⊥) and long term stability. Different steps involved in processing GaSe and GaTe crystals as THz sources and sensors are described.

Influence of light exposure and applied bias on the conductivity of microcrystalline silicon films at room temperature

Microcrystalline silicon films were deposited using the plasma enhanced chemical vapor phase deposition system and SiCl4/H2 gas source. We investigate the evolution of the dark conductivity of the fabricated films afte r a brief exposure to light or under DC bias. Raman spectra measurements indicat e that the volume fractions of crystalline phase for all samples are over 70%. T he measurement of dark resistance reveals the existence of weak persistent photo conductivity in our samples. Under DC electric field, it is found that the dark conductivity increases slowly with time and a restoration process occurs once th e field is reversed. This behavior depends on the DC bias level and the measurem ent temperature and can be explained by a heterojunction barrier model. It is su ggested that the spatial separation and redistribution of charge carriers under applied conditions and the potential barrier associated with inhomogeneity are r esponsible for the observed phenomena.

Structural and transport properties of thermally evaporated nickel phthalocyanine thin films

X-ray diffraction patterns of NiPc in powder form show that it has a β-form with monoclinic structure. The thermal evaporation of NiPc led to α-polycrystalline films orientated preferentially to the (001) plane with an amorphous background. After annealing at 573 K for 2 h, a mixture of α- and β-phases was formed, while the conversion into β-NiPc is completed at 623 K. The dark electrical resistivity has been measured on NiPc films in the temperature range 298–423 K. Two activation energies ΔE1 = 0.12 eV and ΔE2 = 0.76 eV were obtained. The thermal activation energy ΔE1 is associated with impurity conduction and ΔE2 is associated with intrinsic conduction. Thermoelectric power measurement proved that NiPc films are p-type. The thermoelectric power curves also exhibit two different regions corresponding to extrinsic and intrinsic conductions. Room temperature J–V measurements show a linear ohmic dependence at low voltages, followed by SCLC at higher voltage levels, dominated by an exponential distribution of traps with total trap concentration of 2.79 × 1022 m−3.

Terahertz radiation from heavy-ion-irradiated In0.53Ga0.47As photoconductive antenna excited at 1.55μm

We investigate terahertz (THz) emission from heavy-ion-irradiated In0.53Ga0.47As photoconductive antennas excited at 1550 nm. The carrier lifetime in the highly irradiated In0.53Ga0.47As layer is less than 200 fs, the steady-state mobility is 490cm2V−1s−1, and the dark resistivity is 3Ωcm. The spectrum of the electric field radiating from the Br+-irradiated In0.53Ga0.47As antenna extends beyond 2 THz. The THz electric field magnitude is shown to saturate at high optical pump fluence, and the saturation fluence level increases with the irradiation dose, indicating that defect center scattering has a significant contribution to the transient mobility.

Electrical transport properties of thermally evaporated phthalocyanine (H 2Pc) thin films

Thin films of H 2Pc of various thicknesses have been deposited onto glass substrates using thermal evaporation technique at room temperature. The dark electrical resistivity measurements were carried out at different temperatures in the range 298–473 K. An estimation of mean free path ( l o) of charge carriers in H 2Pc thin films was attempted. Measurements of thermoelectric power confirm that H 2Pc thin films behave as a p-type semiconductor. The current density–voltage characteristics of Au/H 2Pc/Au at room temperature showed ohmic conduction mechanism at low voltages. At higher voltages the space-charge-limited conduction (SCLC) accompanied by an exponential trap distribution was dominant. The temperature dependence of current density allows the determination of some essential parameters such as the hole mobility ( μ h), the total trap concentration ( N t), the characteristic temperature ( T t) and the trap density P( E).

Chemical deposition of ZnO films from ammonium zincate bath

Zinc oxide (ZnO) thin films were deposited from ammonium zincate bath following a chemical dipping technique. Films in the thickness range 0.25–4.0 μm could be prepared by varying the ammonium zincate bath concentration (in the range 0.03–1.5 M) and number of dipping (0–200). Higher values of bath concentration produced nonadherent and poor quality films. The film growth rate was found to be a sensitive function of bath pH. The critical range of pH value for adherent and good quality films was found to be 11.0–11.1. Structural characterization by scanning electron microscopy (SEM) and X-ray diffraction (XRD) indicate the formation of polycrystalline ZnO with strong c-axis orientation. The films were found to be highly resistive with dark resistivity of the order of 10 5 Ω cm. The electrical conductance was studied in the temperature range 300–650 K. The characteristic effect of chemisorption was found to influence the electrical properties of the films.

Optoelectronic and electrical properties of TlGaS2 single crystal

AbstractThe optoelectronic and electrical properties of TlGaS2 single crystals have been investigated by means of room temperature transmittance and reflectance spectral analysis, Hall coefficient, dark electrical resistivity and photocurrent measurements in the temperature range of 200–350 K. The optical data have revealed an indirect and direct allowed transition band gaps of 2.45 and 2.51 eV, an oscillator and dispersion energy of 5.04 and 26.45 eV, respectively, a static dielectric constant of 6.25 and static refractive index of 2.50. The dark Hall coefficient measurements have shown that the crystals exhibit a conductivity type conversion from p‐type to n‐type at a critical temperature of 315 K. Deep donor and acceptor energy levels of 0.37/0.36 eV and 0.66 eV has been calculated from the temperature dependence of Hall coefficient and resistivity, and photocurrent measurements, respectively. The photocurrent decreases with decreasing temperature. The analysis of the photocurrent data have revealed that, the recombination mechanism is linear and supralinear above and below 290 K, respectively. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Structural and electrical characterization of S xSe 100− x thin films

Thin films of samples of the glassy S x Se 100− x system with 0 ≤ x ≤ 7.28 have been prepared by thermal evaporation technique at room temperature (300 K). X-ray investigations show that the structure of pure selenium (Se) does change seriously by the addition of small amount of sulphur S ≤7.28%. The lattice parameters were determined as a function of sulphur content. Results of differential thermal analysis (DTA) of the glassy compositions of the system S x Se 100− x were discussed. The characteristic temperatures ( T g, T c and T m) were evaluated. Dark electrical resistivities, ρ, of S x Se 100− x thin films with different thicknesses from 100 to 500 nm, were measured in the temperature range from 300 to 423 K. Two distinct linear parts with different activation energies were observed. The variation of electrical resistivity of examined compositions has been discussed as a function of the film thickness, temperature and the sulphur content. The application of Mott model for the phonon assisted hopping of small polarons gave the same two activation energies obtained from the resistivity temperature calculations.

Growth and Characterization of β‐HgS Thin Films by Annealing Hg2+‐Dithiol Self‐Assembled Multilayers

Hg2+‐dithiol self‐assembled multilayers were constructed by alternatively depositing mercury ion and 1, 6‐hexanedithiol. Cubic β‐HgS thin films were obtained by annealing the self‐assembled Hg2+‐dithiol multilayers at 503 K for 2 h. The grain size was estimated to be 16 nm by use of the Scherrer formula from the XRD pattern. The HgS thin films showed a blue shift in band gap energy due to small grain size. The sheet resistance of the film was sensitive to UV light and the dark resistance was 4.84×104 Ω/2.

Influence of rapid thermal annealing on InAs/InAlAs/InP quantum wires with different InAs deposited thickness

We have studied the effect of the post-growth rapid thermal annealing on optical and electrical properties of InAs/InAlAs/InP quantum wires with various InAs deposited thickness. Quite different annealing behaviors in photoluminescence and dark resistance are observed, which can be attributed to dislocations in samples. After annealing at 800 °C, quantum wires still exist in the sample with two monolayer InAs deposited thickness, but the temperature-dependent PL properties are changed greatly due to the intermixing of In/Al atoms.

Double-frequency properties of In:LiNbO3 crystals

1 mol%, 2 mol%, 3 mol%, 4 mol% and 5 mol% In3+ doped LiNbO3 crystals were grown by the Czochralski method, respectively. Oxidized treatment of some crystals was carried out. The infrared transmission spectra and photo-damage resistance of the samples were measured. The results showed that the OH- absorption peaks of In(3mol%):LiNbO3, In(4mol%):LiNbO3 and In(5mol%):LiNbO3 crystals were located at about 3508 cm-1, while those of In(1mol%):LiNbO3 and In(2mol%):LiNbO3 crystals were located at about 3484cm-1. When the doped In3+ concentration reached its threshold in LiNbO3 crystal, photo-damage resistance of In:LiNbO3 crystals was two orders of magnitude higher than that of pure LiNbO3 crystal. The experimental results of the second harmonic generation (SHG) showed that the phase matching temperatures of In:LiNbO3 crystals were lower than those of Zn:LiNbO3 and Mg:LiNbO3 crystals and the SHG efficiency reached 38%. Oxidization treatment was also found to make the dark trace resistance of crystals increase. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Influence of the growth parameters of p-CdTe thin films on the performance of Au–Cu/p-CdTe/n-CdO type solar cells

R.F. sputter deposition of Sb doped CdTe thin films was carried out with targets containing different amounts of antimony ( C T: 0, 2.5, 10 and 20 at.%). The substrates were kept at different temperatures ( T s) of 200, 275, 350 and 450 °C. Three different argon pressure values: 2.5, 5 and 15 mTorr were used. The lowest dark resistivity ( ρ) at room temperature (RT) was 9.0 × 10 5 Ω cm, which is one of the lowest values reported in the literature for Sb doped CdTe. Highly transparent (∼90%) and conductive ( ρ = 3.7 × 10 −4 Ω cm) F doped CdO (n-type) thin films, prepared at room temperature by the sol–gel method, were employed as window and top-contact. The configuration of the fabricated solar cell was (Au–Cu)/p-CdTe/n-CdO/glass. Open-circuit voltage ( V oc) and short-circuit current density ( J sc) at room temperature have the highest values for high T s, low P g and C T = 10 at.%. Despite the fact that V oc and J sc are lower than those reported in the literature, we think this work is useful as a basis for the search of more competitive CdTe/CdO based PV devices.

ILGAR CuInS 2 films from various preparation conditions

CuInS 2 thin films were prepared by ion layer gas reaction (ILGAR) method using C 2H 5OH as solvent, CuCl and InCl 3 as reagents and H 2S gas as sulfuration source. The effects of cationic precursor concentration and numbers of dipping cycles on characteristics of CuInS 2 film were investigated. The results shows that the chalcopyrite CuInS 2 with near stoichiometry can be deposited as [In 3+] ≤ 0.05 M and [Cu +] ≤ 0.078M ([Cu +]/[In 3+] = 1.55), while Cu x S segregation phase appears with further increasing cationic concentration. Its deposition rate is close to constant as cationic concentration is fixed, and nonlinearly increases with increasing the cationic concentration. CuInS 2 thin film derived from lower cationic concentration is uniform, compact and good in adhesion to the substrates. The absorption coefficient of CuInS 2 thin films is larger than 10 4 cm −1, and the optical band gap E g is 1.30∼1.40 eV and has a slight fall with increase of the cationic concentration. The dark resistivity decreases from ∼50 to ∼10 Ω cm and the carrier concentration ranges over 10 16 cm −3.

Photophysics, photoelectrical properties and photoconductivity relaxation dynamics of quantum-sized bismuth(III) sulfide thin films

Electrical and photoelectrical properties (including both the stationary photoresponse and the photocarriers' relaxation dynamics) of nanocrystalline semiconducting bismuth(III) sulfide thin films were investigated. The experimental design of photoelectrical properties was achieved by controlling the chemistry of the deposition process (varying the reagent concentration in the reaction system) and also by physical means (controlling the crystal dimensions by post-deposition annealing). The band gap energy of thin films characterized by most pronounced photoelectrical properties was calculated, on the basis of measured photoconductivity spectral response curves, by several approaches. All of the obtained values are in very good agreement with the corresponding ones obtained from optical spectroscopy data within the framework of parabolic approximation for dispersion relation. On the basis of measured temperature dependence of dark electrical resistivity of nanocrystalline bismuth(III) sulfide films, the thermal band gap energy and the ionization energy of the impurity level (of donor type) were calculated. The corresponding values are 1.50 and 0.42 eV. Dynamics of non-equilibrium charge carriers' relaxation processes was studied with the oscilloscopic method. By analysis of the photoconductivity decay kinetics data it is found that recombination of non-equilibrium charge carriers is carried out according to the linear mechanism. The calculated relaxation time of photoexcited charge carriers is 1.58 ms, the relaxation processes occurring via local trapping centers. Recombination processes occurring via a single-type trapping center can be described within the framework of the Schockley–Read model. The practically linear regime detected in the measured lux–ampere characteristics of the studied films ( Δ σ ∼ Φ 0.98 ) indicate as well a linear recombination mechanism of the photoexcited charge carriers.