Structural,electrical and optical properties of Ge implanted GaSe single crystals grown by Bridgman technique

Structural, optical and electrical properties of Ge implanted GaSe single crystal have been studied by means of X‐Ray Diffraction (XRD), temperature dependent conductivity and photoconductivity (PC) measurements for different annealing temperatures. It was observed that upon implanting GaSe with Ge and applying annealing process, the resistivity is reduced from 2.1 × 10⁹ to 6.5 × 10⁵ Ω‐cm. From the temperature dependent conductivities, the activation energies have been found to be 4, 34, and 314 meV for as‐grown, 36 and 472 meV for as‐implanted and 39 and 647 meV for implanted and annealed GaSe single crystals at 500°C. Calculated activation energies from the conductivity measurements indicated that the transport mechanisms are dominated by thermal excitation at different temperature intervals in the implanted and unimplanted samples. By measuring photoconductivity (PC) measurement as a function of temperature and illumination intensity, the relation between photocurrent (I_PC) and illumination intensity (Φ) was studied and it was observed that the relation obeys the power law, I_PC αΦⁿ with n between 1 and 2, which is indication of behaving as a supralinear character and existing continuous distribution of localized states in the band gap. As a result of transmission measurements, it was observed that there is almost no considerable change in optical band gap of samples with increasing annealing temperatures for as‐grown GaSe; however, a slight shift of optical band gap toward higher energies for Ge‐implanted sample was observed with increasing annealing temperatures. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structural,optical, and electrical properties of electron beam evaporated CdSe thin films

CdSe films have been deposited on glass substrates at different substrate temperatures between room temperature and 300 °C. The films exhibited hexagonal structure with preferential orientation in the (002) direction. The crystallinity improved and the grain size increased with temperature. Band gap values are found decreasing from about 1.92 eV to 1.77 eV with increase of the substrate temperature. It is observed that the resistivity decreases continuously with temperature. Laser Raman studies show the presence of 2 LO and 3 LO peaks at 416 cm^‐1 and 625 cm^‐1respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal data and some physical properties of Tl2InGaTe4 crystals

The room temperature crystal data, Debye temperature, dark and photoelectrical properties of the Bridgman method grown Tl₂InGaTe₄ crystals are reported for the first time. The X‐ray diffraction technique has revealed that Tl₂InGaTe₄ is a single phase crystal of tetragonal body‐centered structure belonging to the space group. A Debye temperature of 124 K is calculated from the results of the X‐ray data. The current‐voltage measurements have shown the existence of the switching property of the crystals at a critical voltage of 80 V. The dark electrical resistivity and Hall effect measurements indicated the n ‐type conduction with an electrical resistivity, electron density and Hall mobility of 2.49×10³ Ω cm, 4.76×10¹² cm^–3 and 527 cm²V^–1s^–1, respectively. The photosensitivity measurements on the crystal revealed that, the variation of photocurrent with illumination intensity is linear, indicating the domination of monomolecular recombination at room temperature. Moreover, the spectral distribution of the photocurrent allowed the determination of the energy band gap of the crystal studied as 0.88 eV. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Crystal Data,Electrical Resisitivity and Mobility in Cu3In5Se9 and Cu3In5Te9 Single Crystals

X-ray powder diffraction data were obtained for Cu₃In₅Se₉ and Cu₃Te₉, which were found to crystallize in orthorhombic and tetragonal systems, respectively. The electrical resistivities and Hall mobilities of these compounds were investigated in the temperature range 35–475 K. Cu₃In₅Se₉, was identified to be n-type with a room temperature resistivity of 3 × 10³ Ω·cm which decreases with increasing temperature. For T < 65 K impurity activation energy of 0.03 eV and for T > 350 K onset of intrinsic conduction yielding a band gap energy of 0.99eV were detected. The neutral impurity scattering was found to dominate at low temperatures, while in the high temperature region thermally activated mobility was observed. Cu₃In₅Te₉ exhibits p-type conduction with a room temperature resistivity of 8.5 × 10⁻³ Ω·cm decreasing sharply above 400 K and yielding an impurity ionization energy of 0.13 eV. The temperature dependence of mobility indicates the presence of lattice and ionized impuritiy scattering mechanisms above and below 160 K, respectively.     

Influence of substrate temperature on microcrystalline structure and optical properties of ZnTe thin films

ZnTe thin films were deposited onto well‐cleaned glass substrates kept at different temperatures (Ts = 303, 373 and 423 K), by vacuum evaporation method under the pressure of 10^–5 Torr. The thickness of the film was measured by quartz crystal monitor and verified by the multiple beam interferometer method. The structural characterization was made using X‐ray diffractometer with filtered CuKα radiation. The grain sizes of the microcrystallines in films increases with increase in substrate temperature. The strain (ε), grain size (D) and dislocation density (δ) was calculated and results are discussed based on substrate temperature. Optical behaviour of the film was analyzed from transmittance spectra in the visible region (400–800 nm). The optical transition in ZnTe films is direct and allowed type. The optical band gap energy shows an inverse dependence on substrate temperature and thickness. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of ion beam sputtered ZrN coatings prepared at different substrate temperatures

Zirconium nitride (ZrN) coatings were prepared on Si (100) by single ion beam sputtering in N₂ and Ar mixture at different substrate temperatures. Structure and morphology of the ZrN coatings were analyzed using X‐ray diffraction and atomic force microscopy. Rutherford backscattering technique was utilized for the determination of composition and thickness of the coatings. Electrical properties of the ZrN coatings were determined by four point‐ probe and Hall test. The results showed that the growth of ZrN with a preferred (111) orientation was achieved. The coating thickness depended on the substrate temperature and coating surface roughly remained smooth. The resistivity of the coatings varied from 1× 10^‐3 to 14× 10^‐3 Ω cm depending on the substrate temperature. A correlation between resistivity and charge carrier density was established to explain the electrical behavior of the coatings. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Temperature‐tuned band gap energy and oscillator parameters of Tl2InGaSe4 semiconducting layered single crystals

The optical properties of Tl₂InGaSe₄ layered single crystals have been studied through the transmission and reflection measurements in the wavelength range of 500‐1100 nm. The analysis of room temperature absorption data revealed the presence of both optical indirect and direct transitions with band gap energies of 1.86 and 2.05 eV, respectively. Transmission measurements carried out in the temperature range of 10‐300 K revealed that the rate of change of the indirect band gap with temperature is γ = – 4.4 × 10^‐4 eV/K. The absolute zero value of the band gap energy was obtained as E_gi(0) = 1.95 eV. The dispersion of the refractive index is discussed in terms of the single oscillator model. The refractive index dispersion parameters: oscillator wavelength and strength were found to be 2.53 × 10^–7 m and 9.64 × 10¹³ m^–2, respectively. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on the optical constants of zincphthalocyanine thin films

The influence of the film thickness and substrate temperature on optical constants of the vacuum evaporated ZincPhthalocyanine (ZnPc) thin films have been reported in this paper. The direct and allowed optical band gap energy has been evaluated from the (αhυ)² vs. (hυ) plots. The optical constants such as extinction coefficient (k_f) and refractive index (n) have been evaluated from the transmittance values and the observed results strongly dependent on substrate temperature and film thickness. The low values of the refractive index have been observed for the films prepared at T_s=200°C. The change in crystallanity and phase transformation affect the optical constants and the lower values of the optical constants will leads to the good quality of the ZnPc thin films. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Optical and electrical properties of lithium doped nickel oxide films deposited by spray pyrolysis onto alumina substrates

Non-doped and lithium doped nickel oxide crystalline films have been prepared onto quartz and crystalline alumina substrates at high substrate temperature (600 °C) by the pneumatic spray pyrolysis process using nickel and lithium acetates as source materials. The structure of all the deposited films was the crystalline cubic phase related to NiO, although this crystalline structure was a little bit stressed for the films with higher lithium concentration. The grain size had values between 60 and 70 nm, almost independently of doping concentration. The non-doped and lithium doped films have an energy band gap of the order of 3.6 eV. Hot point probe results show that all deposited films have a p-type semiconductor behavior. From current–voltage measurements it was observed that the electrical resistivity decreases as the lithium concentration increases, indicating that the doping action of lithium is carried out. The electrical resistivity changed from 10⁶ Ω cm for the non-doped films up to 10² Ω cm for the films prepared with the highest doping concentration.     

Determination of optical parameters of Ga0.75In0.25Se layered crystals

The optical properties of the Ga_0.75In_0.25Se crystals have been investigated by means of transmission and reflection measurements in the wavelength range of 380–1100 nm. The analysis of the results performed at room temperature revealed the presence of optical indirect transtions with band gap energy of 1.89 eV. The variation of the band gap energy as a function of temperature was also studied in the temperature range of 10–300 K. The rate of change of band gap energy (γ = –6.2 × 10^–4 eV/K) and absolute zero value of the band gap (E_gi(0) = 2.01 eV) were reported. The wavelength dependence of the refractive index was analyzed using Wemple and DiDomenico, Sellmeier and Cauchy models to find the oscillator energy, dispersion energy, oscillator strength and zero‐frequency refractive index values. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The effect of oxygen partial pressure on physical properties of nano‐crystalline silver oxide thin films deposited by RF magnetron sputtering

Nano‐crystalline silver oxide films were deposited on glass and silicon substrates held at room temperature by RF magnetron sputtering of silver target under different oxygen partial pressures. The influence of oxygen partial pressure on the structural, morphological, electrical and optical properties of deposited films was investigated. Varying oxygen partial pressure during the sputter deposition leads to changes of mixed phase of Ag₂O and Ag to a single phase of Ag₂O and to AgO. The X‐ray diffraction and X‐ray photoelectron spectroscopy results showed the formation of single phase Ag₂O with cubic structure at oxygen partial pressures of 2x10^‐2 Pa while the films deposited at higher oxygen partial pressure of 9x10^‐2 Pa showed the formation of single phase of AgO with monoclinic structure. Raman spectroscopic studies on the single phase Ag₂O showed the stretching vibration of Ag‐O bonds. Single‐phase Ag₂O films obtained at oxygen partial pressure of 2x10^‐2 Pa were nano‐crystalline with crystallite size of 20 nm and possessed an electrical resistivity of 5.2x10^‐3 Ωcm and optical band gap of 2.05 eV. The films deposited at higher oxygen partial pressure of 9x10^‐2 Pa were of AgO with electrical resistivity of 1.8x10^‐2 Ωcm and optical band gap of 2.13 eV. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Correlation between growth orientation and growth temperature for bismuth tri‐iodide films

This paper reports the growth of bismuth tri‐iodide thick films intended for direct and digital X‐ray imaging. Films were grown by the vertical physical vapor deposition method, onto glass substrates 2″x 2″ in size, with gold previously deposited as rear electrode. The film thickness was up to 33 μm (±5 %). Optical microscopy and SEM were performed on the films and grain size resulted to be up to 40 μm. A strong correlation was found between the microcrystals growth orientation and the growth temperature. At low temperatures, microcrystals grow with their c axis parallel to the substrate, whereas at higher temperatures, they grow with their c axis perpendicular to the substrate. The higher the growth temperature, the lower the dark current of the film, and the higher the resistivity, which was from 10¹³ to 10¹⁵ Ωcm. A sensitivity to X‐rays of 6.9 nC/R.cm² was measured irradiating the films with X‐rays from a mamographer. Film properties were correlated with the growth temperature, with previous results for bismuth tri‐iodide films and monocrystals and with data for films of alternative materials such as lead and mercuric iodide. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Carrier Scattering Mechanisms in GaS0.5Se0.5 Layered Crystals

Systematic dark electrical resistivity and Hall mobility measurements have been carried out in the temperature range 150‐400 K on n‐type GaS_0.5Se_0.5 layered crystals. The analysis of temperature dependent electrical resistivity and carrier concentration reveals the extrinsic type of conduction with a donor impurity level located at 0.44 eV, donor and acceptor concentrations of 3.4 ×10¹⁷ and 4.1×10¹⁶ cm^‐3, respectively, and an electron effective mass of 0.41 m₀. The Hall mobility is limited by the electron‐phonon short‐range interactions scattering at high temperatures combined with the ionized impurity scattering at low temperatures. The electron‐phonon short‐range interactions scattering mobility analysis reveals an electron‐phonon coupling constant of 0.25 and conduction band deformation potential of 5.57 eV/Å.     

Structural and optoelectrical properties of Ga‐doped ZnO semiconductor thin films grown by magnetron sputtering

Transparent conductive gallium‐doped zinc oxide (Ga‐doped ZnO) films were prepared on glass substrate by magnetron sputtering. The influence of substrate temperature on structural, optoelectrical and surface properties of the films were investigated by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), spectrophotometer, four‐point probe and goniometry, respectively. Experimental results show that all the films are found to be oriented along the c‐axis. The grain size and optical transmittance of the films increase with increasing substrate temperature. The average transmittance in the visible wavelength range is above 83% for all the samples. It is observed that the optoelectrical property is correlated with the film structure. The Ga‐doped ZnO film grown at the substrate temperature of 400 °C has the highest figure of merit of 1.25 × 10⁻² Ω⁻¹, the lowest resistivity of 1.56 × 10⁻³ Ω·cm and the highest surface energy of 32.3 mJ/m².     

Physical Properties of Zinc Oxide Films Prepared by dc Reactive Magnetron Sputtering at Different Sputtering Pressures

Thin films of zinc oxide were deposited by dc reactive magnetron sputtering onto glass substrates held at a temperature of 663 K and oxygen partial pressure of 1x10^‐3 mbar, and at different sputtering pressures in the range 3x10^‐2 ‐ 10x10^‐2 mbar. The effect of sputtering pressure on the structural, electrical and optical properties of the films were systematically studied. The films were polycrystalline in nature with preferred (002) orientation. The temperature dependence of Hall mobility indicated that the grain boundary scattering of the charge carriers are predominant in these films. The films formed at a sputtering pressure of 6x10^‐2 mbar showed a low electrical resistivity of 6.9x10^‐2 Ohm cm, optical transmittance of 83% with an optical band gap of 3.28 eV.     

Spray pyrolysis deposition and characterization of highly (100) oriented magnesium oxide thin films

Transparent dielectric thin films of MgO has been deposited on quartz substrates at different temperatures between 400 and 600°C by a pneumatic spray pyrolysis technique using Mg(CH₃COO)₂·4H₂O as a single molecular precursor. The thermal behavior of the precursor magnesium acetate is described in the results of thermogravimetry analysis (TGA) and differential thermal analysis (DTA). The prepared films are reproducible, adherent to the substrate, pinhole free and uniform. Amongst the different spray process parameters, the substrate temperature effect has been optimized for obtaining single crystalline and transparent MgO thin films. The films crystallize in a cubic structure and X‐ray diffraction measurements have shown that the polycrystalline MgO films prepared at 500°C with (100) and (110) orientations are changed to (100) preferred orientation at 600°C. The MgO phase formation was also confirmed with the recorded Fourier Transform Infrared (FTIR) results. The films deposited at 600°C exhibited highest optical transmittivity (>80%) and the direct band gap energy was found to vary from 4.50 to 5.25 eV with a rise in substrate temperature from 500 to 600°C. The measured sheet resistance and the resistivity of the film prepared at 600°C were respectively 10¹³Ω/□ and 2.06x10⁷Ω cm. The surface morphology of the prepared MgO thin films was examined by atomic force microscopy. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on the properties of electron beam evaporated ZnSe films

ZnSe films were deposited on glass substrates keeping the substrate temperatures, at room temperature (RT), 75, 150 and 250 °C. The films have exhibited cubic structure oriented along the (111) direction. Both the crystallinity and the grain size increased with increasing deposition temperature. A very high value of absorption co‐efficient (10⁴ cm^‐1) is observed. The band gap values decrease from a value of 2.94 eV to 2.69 eV with increasing substrate temperature. The average refractive index value is in the range of 2.39 – 2.41 for the films deposited at different substrate temperatures. The conductivity values increases continuously with temperature. Laser Raman spectra showed peaks at 140.8 cm^‐1, 246.7 cm^‐1and 204.5 cm^‐1which are attributable to 2TA LO phonon and TO phonon respectively. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Structure and Optical Properties of dc Reactive Magnetron Sputtered Zinc Oxide Films

Zinc oxide films were deposited on glass substrates in argon and oxygen atmosphere by dc reactive magnetron sputtering using a metallic zinc target. The influence of oxygen pressure and substrate temperature on the structure and optical properties of the films were systematically investigated and optimised the deposition parameters to prepare single phase zinc oxide films with preferred (002) orientation. At an optimum oxygen pressure of 1x10^-3 mbar and substrate temperature of 663 K, the films exhibited an optical transmittance of 83% with a band gap of 3.28 eV.     

Investigation of DTS effect on r.f. magnetron sputtered ZnO thin films

The aim of this study depends on understanding the effect of target‐to‐substrate distance (D_TS) on ZnO thin films deposited by r.f. magnetron sputtering on to glass substrates at room temperature conditions. The D_TS was changed from 35 mm to 65 mm with steps of 5 mm at 165 W and 0.2 Pa. The deposition rate of the films were ranged from 76 Ǻ / min to 146 Ǻ / min, while 10^‐3 Ω.cm was obtained as the resistivity value with the help of four point probe technique. The structural investigations were carried out by using both the x‐ray diffraction (XRD) and high resolution transmission electron microscopy. According to XRD observations, the films were (002) oriented. Surface behaviour of the ZnO films was examined with atomic force microscopy and scanning electron microscopy. The root mean square (RMS) values were varied from 4.6 nm to 22.8 nm. Also, optical properties were obtained from UV–visible spectrophotometer and the transmittances as around 80 %. At 45 mm D_TS value, the minimum resistivity measured as 9 × 10^{− 4} Ω.cm with 76 Ǻ / min deposition rate. The RMS was obtained as 4.9 nm and transmission was measured as 85.30 %, while band gap was 3.45 eV.     

Influence of substrate temperature and oxygen/argon flow ratio on the electrical and optical properties of Ga‐doped ZnO thin films prepared by rf magnetron sputtering

Effects of substrate temperature and atmosphere on the electrical and optical properties of Ga‐doped ZnO thin films deposited by rf magnetron sputtering were investigated. The electrical resistivity of Ga‐doped ZnO (GZO) films decreases as the substrate temperature increases from room temperature to 300°C. A minimum resistivity of 3.3 × 10^–4 Ω cm is obtained at 300°C and then the resistivity increases with a further increase in the substrate temperature to 400°C. This change in resistivity with the substrate temperature is related to the crystallinity of the GZO film. The resistivity nearly does not change with the O₂/Ar flow ratio, R for R < 0.25 but increases rapidly with R for R > 0.25. This change in resistivity with R is also related to crystallinity. The crystallinity is enhanced as R increases, but if the oxygen partial pressure is higher than a certain level (R = 0.25 ± 0.10) gallium oxides precipitate at grain boundaries, which decrease both carrier concentration and mobility. Optical transmittance increases as R increases for R < 0.75. This change in transmittance with R is related to changes in oxygen vacancy concentration and surface roughness with R. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)