Substrate Temperature Range Research Articles

Two-Dimensional Phase Diagram of Nd/Mo(110) System

A two-dimensional phase diagram of the neodymium-on-molybdenum (110) system obtained from the measured superstructures is newly presented in this paper. All structural investigations were performed by reflection high-energy electron diffraction (RHEED) analysis. Nine types of superstructures, namely, the (14×2), (13×2), (11×2), (8×2), (6×2), c(6×2), c(4.5×2), and c(5×3) two-dimensional structures and a one-dimensional periodic structure, appeared for adequate film thicknesses and a range of substrate temperatures.

CO2 gas sensitivity of sputtered zinc oxide thin films

For the first time, sputtered zinc oxide (ZnO) thin films have been used as a CO2 gas sensor. Zinc oxide thin films have been synthesized using reactive d.c. sputtering method for gas sensor applications, in the deposition temperature range from 130–153°C at a chamber pressure of 8·5 mbar for 18 h. Argon and oxygen gases were used as sputtering and reactive gases, respectively. ZnO phase could be crystallized using a pure metal target of zinc. The structure of the films determined by means of X-ray diffraction method indicates that the zinc oxide single phase can be fabricated in this substrate temperature range. The sensitivity of the film synthesized at substrate temperature of 130°C is 2·17 in the presence of CO2 gas at a measuring temperature of 100°C.

Deposition of hydrogenated amorphous silicon (a-Si:H) films by hot-wire chemical vapor deposition (HW-CVD) method: Role of substrate temperature

Hydrogenated amorphous silicon (a-Si:H) thin films were deposited from pure silane (SiH 4) using hot-wire chemical vapor deposition (HW-CVD) method. We have investigated the effect of substrate temperature on the structural, optical and electrical properties of these films. Deposition rates up to 15 Å s −1 and photosensitivity ∼10 6 were achieved for device quality material. Raman spectroscopic analysis showed the increase of Rayleigh scattering in the films with increase in substrate temperature. The full width at half maximum of TO peak ( Γ TO) and deviation in bond angle (Δ θ) are found smaller than those obtained for P-CVD deposited a-Si:H films. The hydrogen content in the films was found <1 at% over the range of substrate temperature studied. However, the Tauc's optical band gap remains as high as 1.70 eV or much higher. The presence of microvoids in the films may be responsible for high value of band gap at low hydrogen content. A correlation between electrical and structural properties has been found. Finally, the photoconductivity degradation of optimized a-Si:H film under intense sunlight was also studied.

Texture and magnetic properties of hard magnetic RE–Fe–B thin films deposited on a Nb buffer layer

RE–Fe–B thin films with a strong c-axis texture were prepared by dc magnetron sputtering on to a Nb (1 1 0) buffer layer on thermally oxidized Si substrates. The microstructure and magnetic properties of these RE–Fe–B films were studied as a function of the deposition temperature and Fe:RE ratio. The degree of c-axis orientation improved with decreasing deposition temperature. Good perpendicular hard magnetic properties could be obtained over a wide substrate temperature and concentration range. Perpendicular coercivities up to 1.67 MA/m (2.1 T) were obtained for RE-rich films, while perpendicular maximum energy products up to 200 kJ/m 3 were achieved for high Fe content films. Our results show that Nb, as for Ta, is a suitable buffer layer for deposition of highly textured hard magnetic RE 2Fe 14B films.

Structural order and magnetic properties of Fe 3Si/Si(100) heterostructures grown by pulsed-laser deposition

The single-phase Fe 3Si thin films with preferred (220) growth orientation were prepared on Si(100) substrates by pulsed-laser deposition. Different states of order were developed by changing the substrate temperature from room temperature to 500 °C. X-ray diffraction, Mössbauer spectroscopy and macroscopic magnetic measurements were used to analyze changes of structural order and magnetic properties with the substrate temperature. The results show that over the whole range of substrate temperatures considered all films are of Fe 3Si single phase, highly oriented along the (220) plane. With increasing the substrate temperature, the structural order type changes from A2 through B2 to DO 3 and the order degree gradually increases. Meanwhile, the saturation magnetization remarkably decreases with the increase of the substrate temperature, induced by Si segregation from the substrate and embedment into the film probably as the amorphous phase. The room temperature grown film has a high saturation magnetization of 917 kA m − 1 , which nearly equals that of bulk DO 3-Fe 3Si.

AlGaN/GaN HEMTs on free-standing GaN substrates: MBE growth and microwave characterization

We investigate the role of substrate temperature and gallium flux on the DC and microwave properties of AlGaN/GaN high electron mobility transistors grown by molecular-beam epitaxy on free standing, hydride vapor phase epitaxy grown GaN substrates. The free-standing substrates have threading dislocation densities below 10 7 cm −2. We find that AlGaN/GaN heterostructures with excellent properties may be grown within a wide range of substrate temperatures and fluxes. Electron Hall mobilities above 1700 cm 2/V s and sheet resistances below 370 Ω/□ are typical. We are able to obtain high saturated drain currents with low gate leakage. Off-state breakdown voltages as high as 200 V with low drain and gate leakage currents have been measured. Further, we have measured microwave output power densities above 5 W/mm at 4 GHz with a power-added efficiency of 46% and an associated gain of 13.4 dB. We attribute improved electrical properties in these devices to the reduced threading dislocation density compared to those grown on non-native substrates.

Conditions of nanocomposite structure formation from the vapour phase in Ti–Y system

In this study the method of electron beam deposition of a mixture of titanium and yttrium vapours was used to produce condensates at different ratios of elements in the substrate temperature range from 200 to 800 °C. Condensates consist of grains of yttrium and titanium, the dimensions of which are reduced from the submicron to nanosize scale at lowering of substrate temperature. The temperature of composite transition into the nanosized state depends on yttrium content and can be 200–300 °C higher than in the case of pure titanium. Such structural changes are accompanied by an abrupt increase of microhardness. At the change of yttrium content the microhardness of condensates deposited at the same temperature changes non-monotonically. Possible causes of non-monotonic variation of concentration dependencies in Ti–Y condensate microhardness are discussed.

Synthesis of TiC thin films by CVD from toluene and titanium tetrachloride with nickel as catalyst

Titanium Carbide TiCx was deposited onto quartz substrates by the chemical vapour deposition (CVD) method. TiCx thin films were obtained from titanium tetrachloride (TiCl4) and toluene (C6H5CH3) as carbon source. Deposits were carried out in the range of substrate temperatures from 300 to 1100 °C, with a source gas molar ratio (C6H5CH3/TiCl4 + C6H5CH3 ) of 0.8. There was two deposit processes; the first was to carry out without nickel as catalyst and the second with nickel as catalyst. Results showed that the effect of nickel as catalyst is very relevant to obtain TiCx. TiC0.87 thin films, 0.5 mum thickness, were obtained for deposition temperatures above 900°C using nickel as catalyst. In this case a cubic structure, with a lattice parameter of 4.327 Å and a hardness of 2900 Vickers, was obtained at 1100(0)C. whilst for substrate temperatures between 300 to 900°C with nickel as catalyst amorphous carbon samples were obtained. For the samples prepared without the presence of the nickel as catalyst only C amorphous thin films were obtained for all deposit temperatures.

Growth regimes of CdTe deposited by close-spaced sublimation for application in thin film solar cells

We have systematically investigated the growth of CdTe thin films by Close Spaced Sublimation (CSS). Thin films of CdTe were deposited onto CdS substrates held at temperatures in the range 250 to 550 °C. The effect of substrate temperature and evaporation rate on structure and surface morphology of CdTe films were investigated. Up to 450 °C substrate temperature the growth rate was almost constant and decreased exponentially for higher temperatures. The structures of the CdTe films were determined by XRD and a strong (111) orientation was observed within the temperature range 250 °C–470 °C. Above 470 °C the texture changed to mostly (311) and (220) orientations. Surface morphology and grain size of CdTe growth was determined with AFM and SEM. The morphology of the layers showed three major modes: Columnar grains with a diameter of 0.2 μm and a length of 6 μm for temperatures from 250 °C to 350 °C, pyramidal grains with a diameter of 0.5–1.5 μm up to 470°C and irregular shaped grains with a diameter of 5–10 μm for temperatures up to 550 °C. The roughness increased linearly from 15 nm to 220 nm within the substrate temperature range.

Synthesis and size control of ZnO nanorods by conventional pulsed-laser deposition without catalyst

C-axis oriented ZnO nanorods were grown on both sapphire and silicon substrates by conventional pulsed-laser deposition (PLD) without catalyst. Investigations on the effects of PLD parameters reveal that the nanorods can be synthesized in a relatively wide range of substrate temperatures (550–700 °C) under high oxygen pressures (5–20 Torr). The size control was accomplished by adjusting substrate temperature and background pressure. The photoluminescence properties of the nanorods were closely related to the size difference, surface status and substrate nature.

Ion‐ and Photo‐Analysis of Metal Chelate Reactions on the Semiconductor Surface

AbstractThe continuing advances in miniaturization of semiconductor devices have seriously challenged contact technology. This work explored the chemical reaction involved in the bottom‐up formation of metal contacts using a linear atomic metal string chelate for CVD. The adsorption and thermal reaction of a linear dipyridylamino trichromium chelate on the GaN surface were characterized using x‐ray photoelectron spectroscopy, secondary ion mass spectrometry, and thermal programmed desorption. The chelate may react with GaN at 105 K and chemisorb on the substrate surface via bonding of the chromium atom in the central metal chain after its terminal bond was disrupted. The bonding of dipyridylamino ligands to the central metal chain remained intact during chemisorption. The chromium atom string of the chemisorbed species was inclined to the surface. A change in bonding configuration of the chelate took place as the chelate dose to the substrate was increased. The chemisorbed structure was stable on the surface in the substrate temperature range between 110 K and 260 K. Some dipyridylamino ligands may be detached from the chelate at ˜340 K. At a higher substrate temperature of ˜540 K, additional ligands may dissociate, along with the cleavage of the chemical bond in the central metal chain.

Precursor-dependent structural and electrical characteristics of atomic layer deposited films: Case study on titanium oxide

Thin (10–20 nm) TiO 2 films were atomic layer deposited from TiCl 4, Ti(OC 2H 5) 4, H 2O and H 2O 2 in the substrate temperature range 125–350 °C. The structure, chemical composition and electrical properties were correlated to the process temperature and nature of precursors, whereas the effect of precursors on conduction mechanisms was considerable only in the films grown at 125 °C, otherwise controlled by oxide-electrode interfaces. The use of chloride resulted in films with highest permittivity while the use of hydrogen peroxide resulted in lowest permittivity but also in lowest leakage. The post-deposition (pre-metallization) annealing resulted in densification and (re)crystallization of TiO 2 layer but also in thickening of low-permittivity interface layers.

Growth by molecular beam epitaxy and interfacial reactivity of MnSb on InP(0 0 1)

Growth by molecular beam epitaxy of MnSb on InP(0 0 1) has been studied over a range of substrate temperatures (250– 425 ∘ C ) and Sb:Mn flux ratios (2:1 to 8:1). Two growth phases were observed, their predominance mainly dependent on substrate temperature. These have been identified as MnSb (found preferentially at low temperatures) and InSb (found preferentially at high temperatures). The latter phase forms due to In out-diffusion from the substrate, leading to a granular film with increased total thickness and a very rough buried interface. This reaction only occurs in the presence of both Mn and Sb incident fluxes: when exposed to an Sb flux alone, very small islands of InSb are formed at the surface of InP due to residual In clusters but no disruption of the substrate occurs. No such effect was observed for growth on GaAs (0 0 1) and (1 1 1)B. Implications for the growth of hybrid epitaxial systems for semiconductor spintronics are discussed.

Growth model of pentacene on inorganic and organic dielectrics based on scaling and rate-equation theory

We have fabricated a large body of pentacene thin films on different organic and inorganic dielectric materials at four substrate temperatures with different nominal film thicknesses ranging from the submonolayer over the multilayer to the ``thick'' film regime. These films were characterized by atomic force microscopy and analyzed quantitatively by means of scaling and rate equation theory in order to deduce the molecular growth dynamics of pentacene films on organic substrates that are used as gate dielectrics in organic thin film transistors. We found that on all substrates and in the substrate temperature range $25\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}\ensuremath{\leqslant}{T}_{s}\ensuremath{\leqslant}70\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ the growth can be well described as diffusion-limited aggregation. A critical island size of $3\ensuremath{\leqslant}i\ensuremath{\leqslant}4$ was deduced from the scaling of the distribution density of the pentacene grain areas and the power-law dependence of the saturated nucleation density on the deposition rate. This is valid for all substrates in the investigated temperature regime and is also found to be true for $50\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick pentacene films thus emphasizing that the molecule-molecule interaction itself is independent of the underlying surface.

Impact of Drought and Temperature on Growth and Leaf Gas Exchange of Six Bedding Plant Species Under Greenhouse Conditions

The effect of drought on the growth and gas exchange of six bedding plant species—agastache [Agastache urticifolia (Benth.) O. Kuntze `Honeybee Blue'], dusty miller (Cineraria maritima L. `Silverdusty'), petunia (Petunia ×hybrida `Wave Purple'), plumbago (Plumbago auriculata Lam. `Escapade'), ornamental pepper (Capsicum annuum L. `Black Pearl'), and vinca [Catharanthus roseus (L.) G. Don `Titan']—was quantified under greenhouse conditions. Seeds were sown in January and seedlings were grown in the greenhouse until 18 Apr., when two irrigation treatments—drought (D, ≈18% volumetric moisture content at reirrigation) and control (C, ≈25% volumetric moisture content at reirrigation)—were initiated. Leaf net photosynthetic rate (Pn), stomatal conductance (gs), and transpiration (E) were determined in response to a range of substrate moisture content (from ≈5% to 30% by volume) and temperature (from 20 °C to 40 °C). Dry weight of agastache, ornamental pepper, and vinca was unaffected by drought, whereas that of other species was reduced. Leaf area of plumbago and height of plumbago and vinca were reduced by drought. As substrate moisture content decreased from 25% to 10%, Pn, E, and gs decreased linearly in all species except petunia and plumbago. Leaf net photosynthetic rate of all species declined as leaf temperature increased from 20 °C to 40 °C. In contrast, E of all species, except petunia, increased as temperature increased. Transpiration rate of petunia increased as temperature increased from 20 °C to 30 °C, and then decreased between 30 °C and 40 °C. Although petunia had the highest Pn among the tested species, its Pn and gs declined more rapidly compared with the other species as temperature increased from 20 °C to 40 °C or as substrate moisture content decreased, indicating that petunia was most sensitive to high temperature and drought.

Explosive crystallization in the presence of melting

Received 18 January 2006; published 24 May 2006 An experimental investigation of explosive crystallization EC of thin amorphous Ge films deposited on a solid substrate is performed, and a theory of EC front propagation accompanied by melting in a class of films that includes Ge films is developed. The experiments show that the propagation of a planar EC front is possible for a certain range of substrate temperatures and film thicknesses. It is found that for substrate temperatures larger than a certain threshold, the macroscopically planar front leaves behind a columnar microstructure in the crystal. The theory of EC front propagation is based on the experimental observation that the propagating front exhibits a thin layer of Ge melt between the amorphous and crystalline phases. A uniformly propagating planar front solution is determined, whose propagation speed is found as a function of the substrate temperature and the heat loss parameter that, in turn, depends on the film thickness. A linear stability analysis of the uniformly propagating EC front with a melting layer is performed. It is found that in a certain interval of substrate temperatures the EC front undergoes a monotonic morphological instability with a preferred wave number that explains the formation of the columnar structures observed in experiments. We also perform a nonlinear analysis describing the evolution of the morphological instability. The interval of substrate temperatures for which the instability is observed, as well as the wavelength of the columnar structure, are found to be in good agreement with experimental observations.

Self-assembly and conformation of tetrapyridyl-porphyrin molecules on Ag(111)

We present a low-temperature scanning tunneling microscopy (STM) study on the supramolecular ordering of tetrapyridyl-porphyrin (TPyP) molecules on Ag(111). Vapor deposition in a wide substrate temperature range reveals that TPyP molecules easily diffuse and self-assemble into large, highly ordered chiral domains. We identify two mirror-symmetric unit cells, each containing two differently oriented molecules. From an analysis of the respective arrangement it is concluded that lateral intermolecular interactions control the packing of the layer, while its orientation is induced by the coupling to the substrate. This finding is corroborated by molecular mechanics calculations. High-resolution STM images recorded at 15 K allow a direct identification of intramolecular features. This makes it possible to determine the molecular conformation of TPyP on Ag(111). The pyridyl groups are alternately rotated out of the porphyrin plane by an angle of 60 degrees.

Effects of substrate temperature on electrical and structural properties of copper thin films

This paper addresses the effects of substrate temperature on electrical and structural properties of dc magnetron sputter-deposited copper (Cu) thin films on p-type silicon. Copper films of 80 and 500nm were deposited from Cu target in argon ambient gas pressure of 3.6mTorr at different substrate temperatures ranging from room temperature to 250°C. The electrical and structural properties of the Cu films were investigated by four-point probe and atomic force microscopy. Results from our experiment show that the increase in substrate temperature generally promotes the grain growth of the Cu films of both thicknesses. The RMS roughness as well as the lateral feature size increase with the substrate temperature, which is associated with the increase in the grain size. On the other hand, the resistivity for 80nm Cu film decreases to less than 5μΩ-cm at the substrate temperature of 100°C, and further increase in the substrate temperature has not significantly decreased the film resistivity. For the 500nm Cu films, the increase in the grain size with the substrate temperature does not conform to the film resistivity for these Cu films, which show no significant change over the substrate temperature range. Possible mechanisms of substrate-temperature-dependent microstructure formation of these Cu films are discussed in this paper, which explain the interrelationship of grain growth and film resistivity with elevated substrate temperature.

Substrate temperature dependence of microcrystalline silicon growth by PECVD technique

Undoped hydrogenated silicon films have been prepared from a gas mixture of silane and hydrogen, varying substrate temperature from 180–380°C in an ultrahigh vacuum system using RFPECVD technique. XRD and Raman measurements enable us to know that the films are microcrystalline throughout the substrate temperature range. Bond formation of the SiH films at different substrate temperature is studied through different characterisation techniques like Fourier transform infrared spectroscopy and hydrogen evolution study. The infrared absorption spectroscopy and hydrogen evolution study reveal two types of growth: the formation of a void rich material at low Ts (∼180°C) and a compact material at comparatively higher Ts.

Atomic Layer Deposition and Properties of Lanthanum Oxide and Lanthanum‐Aluminum Oxide Films

AbstractAtomic layer deposition (ALD) of lanthanum oxide on glass and silicon substrates was examined using lanthanum silylamide, La[N(SiMe3)2]3, and water as precursors in the substrate temperature range of 150–250 °C. The effect of pulse times and precursor evaporation temperature on the growth rate and refractive index was investigated. The films remained amorphous regardless of the deposition conditions. The resulting La2O3 films contained noticeable amounts of hydrogen and silicon and were chemically unstable while stored in ambient air. Lanthanum aluminum oxide films were achieved with stoichiometry close to that of LaAlO3 at 225 °C from La[N(SiMe3)2]3, Al(CH3)3, and H2O. The lanthanum β‐diketonate precursor, La(thd)3, was used as the reference precursor.