Influence of substrate temperature on the structure of ZnO:Al thin films

ZnO: Al films were prepared using low cost spray pyrolysis technique. The dependence of the physical properties on the substrate temperature was studied. The best films obtained at 500°C substrate temperature with preferred [002] orientation. The sheet resistance decreases with increased substrate temperature, and values as low as R_sh = 207 Ω/cm² are reached for substrate temperature of 500°C. The optical transmittance of films increased by increasing the substrate temperature and received to 75% at 500°C. (© 2007 WILEY ‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

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)     

Growth chemistry of nanocrystalline silicon and germanium films

We report on the growth of nanocrystalline Si:H and Ge:H films. The films were grown using plasma deposition and hot wire chemical growth techniques. Conditions such as pressure, temperature and hydrogen dilution were systematically varied. It is shown that excessive hydrogen dilution during growth leads to smaller grains in nanocrystalline Si and Ge. Films with very large grains (56 nm) could be obtained using hot wire growth techniques under appropriate conditions of growth. From the data, it is concluded that the natural growth direction for the films is 〈2 2 0〉, and that excessive bonded hydrogen leads to smaller grains.     

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)     

Influence of temperature on the microcrystalline structure of thermally evaporated Sb2S3 thin films

Thin films of antimony trisulfide (Sb₂S₃) were prepared by thermal evaporation under vacuum (p=5×10^–5 torr) on glass substrates maintained at various temperatures between 293 K and 523 K. Their microstructural properties have obtained by transmission electron microscopy (TEM). The electron diffraction analysis showed the occurrence of amorphous to polycrystalline transition in the films deposited at higher temperature of substrates (523 K). The polycrystalline thin films were found to have an orthorhombic structure. The interplanar distances and unit‐cell parameters were determined by high‐resolution transmission electron microscopy (HRTEM) and compared with the standard values for Sb₂S₃. The surface morphology of Sb₂S₃ thin films was investigated by scanning electron microscopy (SEM). The optical transmission spectra at normal incidence of Sb₂S₃ thin films have been measured in the spectral range of 400–1400 nm. The analysis of the absorption spectra revealed indirect energy gaps, characterizing of amorphous films, while the polycrystalline films exhibited direct energy gap. From the photon energy dependence of absorption coefficient, the optical band gap energy, E_g, were calculated for each thin films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Electrical conductivity and photoreflectance of nanocrystalline copper nitride thin films deposited at low temperature

Nanocrystalline thin films of copper nitride were grown on Si (1 0 0) wafers at a low substrate temperature by reactive magnetron sputtering of Cu target with the mixture of nitrogen and argon. The influence of nitrogen deficiency upon the structural, optical and electrical properties of as-deposited films was investigated. X-ray diffraction confirms the presence of cubic Cu₃N and Cu biphases irrespective of carefully optimized processing parameters. With a Cu content approaching the stoichiometry for Cu₃N, the films assume a smooth morphology with densely-packed nanocrystallites of about 40–60 nm in size. Those deposits containing more than 79% Cu are metallic conductors with excellent electrical conductivity via a percolation mechanism, whereas the slightly substoichiometric Cu₃N films show a typical behavior of deficit semiconductor, with an optical gap of about 1.85 eV as revealed by photoreflectance measurement. All the observations are discussed in terms of nitrogen reemission from the growing film.     

High intense UV-luminescence of nanocrystalline ZnO thin films prepared by thermal oxidation of ZnS thin films

High quality zinc oxide (ZnO) films were obtained by thermal oxidation of high quality ZnS films. The ZnS films were deposited on a Si substrate by a low-pressure metalorganic chemical vapor deposition technique. X-ray diffraction spectra indicate that high quality ZnO films possessing a polycrystalline hexagonal wurtzite structure with preferred orientation of (0 0 2) were obtained. A fourth order LO Raman scattering was observed in the films. In photoluminescence (PL) measurements, a strong PL with a full-width at half-maximum of 10 nm around 380 nm was obtained for the samples annealed at 900°C at room temperature. The maximum PL intensity ratio of the UV emission to the deep-level emission is 28 at room temperature, providing evidence of the high quality of the nanocrystalline ZnO films.     

Properties of n-type hydrogenated nanocrystalline cubic silicon carbide films deposited by VHF-PECVD at a low substrate temperature

n-Type hydrogenated nanocrystalline cubic silicon carbide (nc-3C–SiC:H) films have been deposited by very high-frequency plasma-enhanced chemical vapor deposition at a low substrate temperature of about 360 °C to apply this material to the window layer of heterojunction crystalline silicon (HJ-c-Si) solar cells. We investigated the effect of in situ doping on deposition rate, crystalline volume fraction and dark conductivity to optimize properties of the material. We also fabricated HJ-c-Si solar cells with a n-type nc-3C–SiC:H window layer. The solar cells shows high internal quantum efficiency of 0.90 at a wavelength of 400 nm, indicating that n-type nc-3C–SiC:H deposited by VHF-PECVD is a promising candidate of the window layer of HJ-c-Si solar cells.     

Effect of substrate temperature on the properties of vacuum evaporated indium selenide thin films

Thin films of InSe were obtained by thermal evaporation techniques on glass substrates maintained at various temperatures (T_sb = 30°, 400°C). X‐ray diffraction analysis showed the occurrence of amorphous to polycrystalline transformation in the films deposited at higher substrate temperature (400°C). The polycrystalline films were found to have a hexagonal lattice. Compositions of these films have been characterized by EDAX and the surface analysis by scanning electron microscopy. Optical properties of the films, investigated by using spectrophotometer transmittance spectra in the wavelength range (300 – 1100 nm), were explained in terms of substrate temperatures. Films formed at room temperature showed an optical band gap (E_g^opt) 1.56 eV; where as the films formed at 400°C were found to have a E_g^opt of 1.92 eV. The increase in the value of E_g^opt with T_sb treatment is interpreted in terms of the density of states model as proposed by Mott and Davis. The analysis of current ‐Voltage characteristics, based on space charge limited currents (SCLC) measurements, confirms the exponential decrease of density of states from the conduction band edge towards the Fermi level for both the amorphous and polycrystalline films. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of the substrate temperature on the structural,optical, and electrical properties of tin selenide thin films deposited by thermal evaporation method

Thin films of tin selenide (SnSe) were deposited on sodalime glass substrates, which were held at different temperatures in the range of 350‐550 K, from the pulverized compound material using thermal evaporation method. The effect of substrate temperature (T_s) on the structural, morphological, optical, and electrical properties of the films were investigated using x‐ray diffraction analysis (XRD), scanning electron microscopy (SEM), transmission measurements, and Hall‐effect characterization techniques. The temperature dependence of the resistance of the films was also studied in the temperature range of 80‐330 K. The XRD spectra and the SEM image analyses suggest that the polycrystalline thin films having uniform distribution of grains along the (111) diffraction plane was obtained at all T_s. With the increase of T_s the intensity of the diffraction peaks increased and well‐resolved peaks at 550 K, substrate temperature, were obtained. The analysis of the data of the optical transmission spectra suggests that the films had energy band gap in the range of 1.38‐1.18 eV. Hall‐effect measurements revealed the resistivity of films in the range 112‐20 Ω cm for films deposited at different T_s. The activation energy for films deposited at different T_s was in the range of 0.14 eV‐0.28 eV as derived from the analysis of the data of low‐temperature resistivity measurements. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of substrate temperature on the properties of vacuum evaporated InSb films

Indium Antimonide (InSb) thin films were grown onto well cleaned glass substrates at different substrate temperatures (303, 373 and 473 K) by vacuum evaporation. The elemental composition of the deposited InSb film was found to be 52.9% (In) and 47.1% (Sb). X‐ray diffraction studies confirm the polycrystallinity of the films and the films show preferential orientation along the (111) plane. The particle size (D), dislocation density (δ) and strain (ε) were evaluated. The particle size increases with the increase of substrate temperature, which was found to be in the range from 22.36 to 32.59 nm. In Laser Raman study, the presence of longitudinal mode (LO) confirms that the deposited films were having the crystalline nature. Raman peak located at 191.26 cm^–1 shift towards the lower frequencies and narrows with increase in deposition temperature. This indicates that the crystallinity is improved in the films deposited at higher substrate temperatures. Hall measurements indicate that the films were p‐type, having carrier concentration ≅10¹⁶ cm^–3 and mobility (4–7.7) ×10³ cm²/Vs. It is observed that the carrier concentration (N) decreases and the Hall mobility (μ) increases with the increase of substrate temperature. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of substrate temperature on polycrystalline Cd0.9Zn0.1Te thin films studied by Raman scattering spectroscopy

Cd_0.9Zn_0.1Te thin films were prepared by vacuum evaporation onto well‐cleaned glass substrates maintained at 300, 373 and 473 K. X‐ray diffraction studies revealed that the films have zinc blende structure with preferential (111) orientation. Raman peak of the room temperature deposited film appeared at 140.30 cm^‐1 and 159.65 cm^‐1 were for the transverse optic (TO) and longitudinal optic (LO) phonons respectively. The XRD patterns of the higher substrate temperature deposited films exhibited an improvement in the crystallinity of the films. The Raman peak intensity increases and the FWHM decreases for the films deposited at higher substrate temperature. (© 2004 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)     

Crystalline growth of germanium thin films on single crystal silicon substrates by solid phase crystallization

We have studied the epitaxial-like growth of germanium (Ge), due to solid phase crystallization (SPC) from amorphous Ge (a-Ge) deposited on single crystal silicon (Si) substrate. The crystalline growth of Ge following the orientation of Si substrates was successfully obtained by the SPC at 400 °C or higher. The preferential growth on Si (111) substrates continues up to 10,000 Å. Different orientations from the substrate orientation in XRD patterns are slightly observed in the growth on Si (100) substrates at 450 °C, but the preferential growth of (100) orientation continued in the whole film thickness in TEM images. The epitaxial-like growth of Ge may be more preferable on the Si (111) substrate than the (100) one.     

Influence of substrate and film thickness on structural,optical and electrical properties of ZnO thin films

Transparent Zinc Oxide (ZnO) thin films have been grown on Si (100) and Sapphire (0001) substrates by RF magnetron sputtering for different growth time intervals (10, 30 and 60 min) to study the substrate and thickness effects. All the films have been grown at a substrate temperature of 450 °C. It has been found that the average growth rate on Si (100) substrate (8.6 nm/min) is higher than that on Sapphire (0001) substrate (2.6 nm/min) in an identical growth condition which clearly shows the virtual role of substrates. The lower growth rate on Sapphire (0001) suggests that the increasingly ordered and uniform growth due to less lattice mismatch. The grown films have been characterized by X‐ray diffraction (XRD), Reflectance, Photoluminescence (PL) and Hall measurements. The XRD result (FWHM) reveals that for lower growth time, the films grown on Si (100) is better than on Sapphire (0001). Conversely, for higher growth time, the films grown on Sapphire (0001) is better than on Si (100). The variation of strain behavior due to thickness on both substrates has been justified by UV‐Vis reflectance, photoluminescence and Hall effect measurements. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Evaluation of charge trapping properties of microcrystalline germanium thin films by Kelvin force microscopy

We have prepared highly-crystallized germanium (Ge) films on quartz and evaluated their local charge trapping and electrical conduction properties from topographic and surface potential images simultaneously taken by a conductive atomic force microscopy (AFM) during and after current application to Ge films. By applying a bias of 10 V at which the current of ~ 8 mA flows between the co-planer electrodes on Ge films, the surface potential image which was uniform before bias application shows in-plane inhomogeneity within ~ 1.0 mV commensurate with the surface morphology. Such potential images remained inhomogeneous at zero bias for more than two hours after bias application. The inhomogeneous potential images can be interpreted in terms of the difference in electron concentration in highly-crystallized Ge films presumably caused by electron charging in the grain boundaries, indicating direct detection of electrically separated grain structures and resultant percolation current pass.     

Influence of the structure of InP thin films on electron energy loss spectra

Electron energy loss measurements were carried out on single crystalline, polycrystalline, and amorphous InP thin films. Plasmon data and structures of − Im ε⁻¹ are discussed in dependence on degree of crystallinity.     

Growth and characterization of zirconium oxide thin films on silicon substrate

The growth and characterization of zirconium oxide (ZrO₂) thin films prepared by thermal oxidation of a deposited Zr metal layer on SiO₂/Si were investigated. Uniform ZrO₂ thin film with smooth surface morphology was obtained. The thermal ZrO₂ films showed a polycrystalline structure. The dielectric constant of the ZrO₂ film has been shown to be 23, and the equivalent oxide thickness (EOT) of the ZrO₂ stacked oxide is in the range of 3.38–5.43 nm. MOS capacitors with ZrO₂ dielectric stack show extremely low leakage current density, less than 10^?6 A/cm² at ?4 V. Consequently, using this method, high-quality ZrO₂ films could be fabricated at oxidation temperature as low as 600 °C.     

Role of halogen in low-temperature growth of polycrystalline thin films by reactive thermal CVD

Low-temperature growth of polycrystalline silicon by reactive thermal CVD, in which a set of reactive gasses are selected to promote film growth and/or crystallization at low-temperatures in thermal CVD, was studied with disilane and halogens such as fluorine and chlorine. High quality polycrystalline Si films were grown on glass substrates in Si₂H₆–F₂ system at 450 °C, while polycrystalline films were hardly deposited when Si₂H₆–Cl₂ system was adapted in the similar condition. We examined the major factors that govern the crystal growth at low-temperature by comparing the experimental results from these two systems. We suggest that the chemical processes on the growing surface in which Si-network is formed while the terminators are eliminated play a significant role for nucleation and growth in the low-temperature deposition by reactive thermal CVD.     

Low temperature plasma deposition of silicon thin films: From amorphous to crystalline

We report on the epitaxial growth of crystalline silicon films on (100) oriented crystalline silicon substrates by standard plasma enhanced chemical vapor deposition at 175 °C. Such unexpected epitaxial growth is discussed in the context of deposition processes of silicon thin films, based on silicon radicals and nanocrystals. Our results are supported by previous studies on plasma synthesis of silicon nanocrystals and point toward silicon nanocrystals being the most plausible building blocks for such epitaxial growth. The results lay the basis of a new approach for the obtaining of crystalline silicon thin films and open the path for transferring those epitaxial layers from c-Si wafers to low cost foreign substrates.