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1.
Doping and electrical characteristics of in-situ heavily B-doped Si 1−x−yGe xC y (0.22< x<0.6, 0< y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH 4–GeH 4–CH 3SiH 3–B 2H 6–H 2 gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH 4 partial pressure, and only at high GeH 4 partial pressure did it decrease with increasing B 2H 6 as well as CH 3SiH 3 partial pressures. With the B 2H 6 addition, the Ge and C fractions scarcely changed and the B concentration ( CB) increased proportionally. The C fraction increased proportionally with increasing CH 3SiH 3 partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si 1−x−yGe xC y with y=0.0054 or below, the carrier concentration was nearly equal to CB up to approximately 2×10 20 cm −3 and was saturated at approximately 5×10 20 cm −3, regardless of the Ge fraction. The B-doped Si 1−x−yGe xC y with high Ge and C fractions contained some electrically inactive B even at the lower CB region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially. 相似文献
2.
B-doped a-Si 1−xC x:H films for a window layer of Si thin film solar cells have been prepared by the Cat-CVD method. It is found that C is effectively incorporated into the films by using C 2H 2 as a C source gas, where an only little C incorporation is observed from CH 4 and C 2H 6 under similar deposition conditions. Using a-Si 1−xC x:H films grown from C 2H 2, heterojunction p–i–n solar cells have been prepared by the Cat-CVD method. The cell structure is (SnO 2 Asahi-U)/ZnO/a-Si 1−xC x:H(p)/a-Si:H(i)/μc-Si:H(n)/Al. The obtained conversion efficiency was 5.4%. 相似文献
3.
First principles electronic structure method based on the density functional theory and the local density approximation is used to investigate the structural and electronic properties of C 3N 4−nP n ( n=0,1,2,3,4). It is found that the N-rich compounds energetically favor structures with sp 2 bonding, while the pseudocubic structure which is characterized by sp 3 bonding is preferred by the P-rich compounds. Even though C 3N 4 is a wide-gap semiconductor, the band gap of C 3N 4−nP n decreases rapidly when N is gradually substituted with P, and the P-rich compounds are predicted to be metallic or narrow-gap semiconductors. 相似文献
4.
We propose a new approach to fabrication of hydrogenated amorphous silicon carbide (a-Si 1−xC x:H) thin films for solar cells by the catalytic chemical vapor deposition (Cat-CVD) method using a carbon catalyzer, which is more stable than tungsten or tantalum. It was found that by using the carbon catalyzer, undoped and boron-doped a-Si 1−xC x:H films were easily obtained from a SiH 4, CH 4 and B 2H 6 mixture without any change in the catalyzer surface, even after deposition for longer than 30 h. 相似文献
5.
Thick film H 2 sensors were fabricated using SnO 2 loaded with Ag 2O and PdO x. The composition that gave highest sensitivity for H 2 was in the wt.% ratio of SnO 2:Ag 2O:PdO x as 93:5:2. The nano-crystalline powders of SnO 2–Ag 2O–PdO x composites synthesized by sol–gel method were screen printed on alumina substrates. Fabricated sensors were tested against gases like H 2, CH 4, C 3H 8, C 2H 5OH and SO 2. The composite material was found sensitive against H 2 at the working temperature 125 °C, with minor interference of other gases. H 2 gas as low as 100 ppm can be detected by the present fabricated sensors. It was found that the sensors based on SnO 2–Ag 2O–PdO x nanocrystalline system exhibited high performance, high selectivity and very short response time to H 2 at ppm level. These characteristics make the sensor to be a promising candidate for detecting low concentrations of H 2. 相似文献
6.
Cat-CVD method has been applied to the growth of Si–C and Si–C–O alloy thin films. Growth mechanism has been studied with emphasis on the effects of filament materials. Growth rates and alloy compositions were measured for W, Ta, Mo and Pt filaments at the filament temperatures ranging from 1300 to 2000 °C. Si 1−xC x films with x ranging from 0.38 to 0.7 could be grown by using single molecule source Si(CH 3) 2H 2 (dimethylsilane). Si–C–O ternary alloy films was successfully prepared by using Si(OC 2H 5) 4 (tetraethoxysilane) and Si(CH 3) 2(OCH 3) 2 (dimethyldimethoxysilane) molecules. 相似文献
7.
(Ti 1−xAl x)N films were prepared on a Si wafer at 700°C from toluene solution of alkoxides (titanium tetraetoxide and aluminum tri-butoxide) in an Ar/N 2/H 2 plasma by the thermal plasma chemical vapor deposition (CVD) method. The films were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, electrical resistivity, and Vickers micro-hardness. Single phase TiN formed at an Al atomic fraction of 0–0.2, with a mixed TiN and AlN phase occurring up to 0.6 and single phase AlN forming above 0.8. The films had relatively sooth surfaces, 0.4 μm thick at an Al atomic fraction of 0.2, and thickened with increasing Al fraction. The atomic concentration of Ti, Al, N, O, and C determined from their respective XPS areas showed that the Ti and Al contents of the films changes with the solution composition in a complementary way. The impurities were about 10 at.% oxygen and carbon. The electrical resistivity was almost unchanged from the value of 10 3 μΩ cm at 0–0.6 Al but then suddenly increased to 10 4 μΩ cm at higher Al contents. The hardness showed a synergic maximum of about 20 GPa at an Al fraction of 0.6–0.8. 相似文献
8.
In 2O 3 thin films have been prepared from commercially available pure In 2O 3 powders by high vacuum thermal evaporation (HVTE) and from indium iso-propoxide solutions by sol-gel techniques (SG). The films have been deposited on sapphire substrates provided with platinum interdigital sputtered electrodes. The as-deposited HVTE and SG films have been annealed at 500°C for 24 and 1 h, respectively. The film morphology, crystalline phase and chemical composition have been characterised by SEM, glancing angle XRD and XPS techniques. After annealing at 500°C the films’ microstructure turns from amorphous to crystalline with the development of highly crystalline cubic In 2O 3−x (JCPDS card 6-0416). XPS characterisation has revealed the formation of stoichiometric In 2O 3 (HVTE) and nearly stoichiometric In 2O 3−x (SG) after annealing. SEM characterisation has highlighted substantial morphological differences between the SG (highly porous microstructure) and HVTE (denser) films. All the films show the highest sensitivity to NO 2 gas (0.7–7 ppm concentration range), at 250°C working temperature. At this temperature and 0.7 ppm NO 2 the calculated sensitivities ( S= Rg/ Ra) yield S=10 and S=7 for SG and HVTE, respectively. No cross sensitivity have been found by exposing the In 2O 3 films to CO and CH 4. Negligible H 2O cross has resulted in the 40–80% relative humidity range, as well as to 1 ppm Cl 2 and 10 ppm NO. Only 1000 ppm C 2H 5OH has resulted to have a significant cross to the NO 2 response. 相似文献
9.
High quality GaN epitaxial layers were obtained with Al xGa 1−xN buffer layers on 6H–SiC substrates. The low-pressure metalorganic chemical vapor deposition (LP-MOCVD) method was used. The 500 Å thick buffer layers of Al xGa 1−xN (0≤ x≤1) were deposited on SiC substrates at 1025°C. The FWHM of GaN (0004) X-ray curves are 2–3 arcmin, which vary with the Al content in Al xGa 1−xN buffer layers. An optimum Al content is found to be 0.18. The best GaN epitaxial film has the mobility and carrier concentration about 564 cm 2 V −1 s −1 and 1.6×10 17 cm −3 at 300 K. The splitting diffraction angle between GaN and Al xGa 1−xN were also analyzed from X-ray diffraction curves. 相似文献
10.
The Ba xSr 1−xTiO 3 (BST)/Pb 1−xLa xTiO 3 (PLT) composite thick films (20 μm) with 12 mol% amount of xPbO–(1 − x)B 2O 3 glass additives ( x = 0.2, 0.35, 0.5, 0.65 and 0.8) have been prepared by screen-printing the paste onto the alumina substrates with silver bottom electrode. X-ray diffraction (XRD), scanning electron microscope (SEM) and an impedance analyzer and an electrometer were used to analyze the phase structures, morphologies and dielectric and pyroelectric properties of the composite thick films, respectively. The wetting and infiltration of the liquid phase on the particles results in the densification of the composite thick films sintered at 750 °C. Nice porous structure formed in the composite thick films with xPbO–(1 − x)B 2O 3 glass as the PbO content ( x) is 0.5 ≥ x ≥ 0.35, while dense structure formed in these thick films as the PbO content ( x) is 0.8 ≥ x ≥ 0.65. The volatilization of the PbO in PLT and the interdiffusion between the PLT and the glass lead to the reduction of the c-axis of the PLT phase. The operating temperature range of our composite thick films is 0–200 °C. At room temperature (20 °C), the BST/PLT composite thick films with 0.35PbO–0.65B 2O 3 glass additives provided low heat capacity and good pyroelectric figure-of-merit because of their porous structure. The pyroelectric coefficient and figure-of-merit FD are 364 μC/(m 2 K) and 14.3 μPa −1/2, respectively. These good pyroelectric properties as well as being able to produce low-cost devices make this kind of thick films a promising candidate for high-performance pyroelectric applications. 相似文献
11.
The E1 and E1+Δ 1 energy bands of metal–organic chemical vapor deposition grown Al xGa 1−xAs, with x in the range 0–0.55, have been determined using photoreflectance technique. The aluminum composition for each sample was determined using the energy of the room-temperature photoluminescence compensated peak value and a suitable fundamental band gap formula. The positions of the E1 and E1+Δ 1 peaks were determined from curve-fitting an appropriate theoretical model to our experimental data by a modified downhill simplex method. Using the results, we propose new E1 and E1+Δ 1 cubic expressions as functions of the aluminum composition, x, and compare them with the available reported expressions. 相似文献
12.
Microcrystalline silicon carbide (μc-Si 1−xC x) films were successfully deposited by the hot wire cell method using a gas mixture of SiH 4, H 2 and C 2H 2. It was confirmed by Fourier transform infrared and X-ray diffraction analyses that the films consisted of μc-Si grains embedded in a-Si 1−xC x tissue. The p-type μc-Si 1−xC x films were deposited using B 2H 6 as a doping gas. A dark conductivity of 0.2 S/cm and an activation energy of 0.067 eV were obtained. The p-type μc-Si 1−xC x was used as a window layer of a-Si solar cells, in which the intrinsic layer was deposited by photo-chemical vapor deposition, and an initial conversion efficiency of 10.2% was obtained. 相似文献
13.
AgInSn xS 2−x ( x = 0–0.2) polycrystalline thin films were prepared by the spray pyrolysis technique. The samples were deposited on glass substrates at temperatures of 375 and 400 °C from alcoholic solutions comprising silver acetate, indium chloride, thiourea and tin chloride. All deposited films crystallized in the chalcopyrite structure of AgInS 2. A p-type conductivity was detected in the Sn-doped samples deposited at 375 °C, otherwise they are n-type. The optical properties of AgInSn xS 2−x ( x < 0.2) resemble those of chalcopyrite AgInS 2. Low-temperature PL measurements revealed that Sn occupying an S-site could be the responsible defect for the p-type conductivity observed in AgInSn xS 2−x ( x < 2) thin films. 相似文献
14.
Selective wet chemical etching of the Al xGa 1−xAs/GaAs system has been applied to heterostructure characterization. Samples of LPE grown AlGaAs/GaAs laser double-heterostructures and separate confinement heterostructures as well as antiresonant reflecting optical waveguides heterostructures were treated with “I2 solution” (I 2:KI:H 2O) and hydrochloric acid. These compounds selectively etch the ternary Al xGa 1−xAs layers, but with different “threshold composition” xth values (the x value is that above which the etching rate of a given compound increases sharply). Selectively etched samples have been examined by SEM. The experimental dependence of etching rate on the x value for I2 solution has been derived. From this dependence, the x composition of any ternary layer can be estimated simply. Observations were made of the “microscopic” properties of the heterostructure, such as the smoothness of the interfaces and the uniformity of layers. All imperfections resulting from the growth process, such as interface perturbations or compositional nonuniformity of layers, are clearly seen. An additional advantage of this etching technique is its simplicity. It allows quick examination of grown heterostructure for the selection of wafers for further processing. 相似文献
15.
The mechanical properties like hardness, Hv and compressive strength, σ of Ni 1−xZn xFe 2O 4 ( x = 0.2, 0.3, 0.4 and 0.5) prepared by the non-conventional flash combustion and citrate-gel decomposition techniques are studied and reported. It is observed that there is an increase in hardness with zinc content as well as sintering temperature. The hardness in the order of 2.0–3.63 GPa and compressive strength in the order of 150–240 MPa are obtained for Ni–Zn ferrites prepared by these non-conventional techniques. The influence of density, porosity and microstructure on hardness and compressive strength of Ni–Zn ferrites with respect to sintering temperature was studied. 相似文献
16.
以有机钛源钛酸四正丁酯(Ti(OC 4H 9) 4)与纳米碳黑(C)为反应原料制备超细Ti(C 1-xN x)粉体。经过计算可知两者理论质量比约为9.4:1,以 m(Ti(OC 4H 9) 4): m(C)=9:1混料,通过溶胶凝胶法制备烧结前驱体。利用高温碳热还原法,在N 2气氛中,分别在不同温度下恒温烧结1 h,直接反应合成超细Ti(C 1-xN x)粉体。结果发现,随温度升高, x 值逐渐降低,数值区间为0.19~0.72;产物组分中的总碳含量(C t)逐渐增大,从14.23wt%增大到18.66wt%,游离碳含量(C f)与氧含量(C o)均低于0.5wt%;产物平均粒度也呈增大趋势,平均粒度分布区间为220~275 nm。 相似文献
17.
Vickers microhardness indentations of 10 μm (001) oriented epilayers of Al xGa 1−xAs on GaAs substrates have been utilized to evaluate the hardness Hv, the internal stress, and the fracture toughness KIc of the layers as a function of their composition parameter x. The hardness Hv varies linearly according to: (6.9-2.2 x) GPa and KIc increases linearly with x according to: K1c = (0.44+1.30 x) MPa m 1/2. The influence of the substrate on these measurements was found to be negligible for the layer thickness (10 μm) and the indentation load (0.25 N) used, disregarding internal stresses. Internal film stresses were evaluated by the bimorph buckling method, and were found to depend on the composition parameter according to σ = 0.13x GPa. These stresses did not notably affect the Hv measurements, but for KIc corrections as large as 25% had to be made. The radial cracks observed were of the shallow Palmqvist type. In contradiction to previous reports on this type of cracking, it was found to initiate during unloading, not during loading, and a physical explanation for this deviation is given. No deep radial/median cracks were observed. It was found important to use expressions based on the correct crack geometry in the KIc evaluation. Also, a simple theory for the influence of internal stresses on the KIc results has been developed. 相似文献
18.
Polyacrylonitrile (PAN) based high strength carbon fibers were anodically oxidized using the galvanostatic mode in alkaline electrolyte solutions to influence the chemical surface composition. The change of chemical and physical properties was investigated using scanning electron microscopy (SEM), photoelectron spectroscopy (XPS), energy dispersive X-ray analysis (EDX) and contact angle as well as zeta ( ζ)-potential measurements. An initially improved wettability for polar liquids, particularly water, was observed for oxidized carbon fibers. This result was confirmed by ζ-potential measurements. The chemical state of the oxygen containing surface groups changes during anodic oxidation in K2CO3/KOH due to further oxidation of C–OH and C=O groups to COOH groups. Therefore the surface acidity increases, which leads to a shift of the isoelectric point to lower pH values and increases the negative ζplateau value. The ζ–pH as well as the ζ–concentration dependence show the same tendency. During anodic oxidation of carbon fibers in KNO3/KOH electrolyte solution beside ‘normal’ (like C–OH, C=O and COOH) surface oxides also carboxylate groups (COO−K+) were formed at the fiber surface in contrast to an oxidation in K2CO3/KOH which introduces ‘normal' surface oxides. No influence could be observed of such an anodic oxidation on the single fiber tensile strength. Contact angle measurements of polycarbonate melt droplets onto single carbon fibers show no dependence of the surface composition. The interfacial shear strength, measured using the microdroplet pull-off test were compared with the thermodynamic work of adhesion. The calculated as well as the measured adhesion show the same absence of any influence of fiber treatment. 相似文献
19.
Symmetric CN x/BN:C multilayer thin films, with nominal compositional modulation periods of Λ=2.5, 5, and 9 nm were deposited by unbalanced dual cathode magnetron sputtering from C (graphite) and B 4C targets in an Ar/N 2 (60/40) discharge. The multilayers and single-layer of the constituent CN x and BN:C compounds were grown to a total thickness of 0.5 μm onto Si(001) substrates held at 225°C and a negative floating potential of 30 V ( Ei≈24 eV). Layer characterizations were performed by TEM, X-ray reflectivity, RBS, and nanoindentation measurements. Results show that CN 0.33 and BN:C (35, 50, and 15 at.% of B, N, and C, respectively) layers were prepared at the above conditions. It is suggested that all films exhibit a three-dimensional interlocked structure with a cylindrical texture in the film growth direction. The structure was continuous over relatively well defined and smooth CN x/BN:C interfaces. All coatings exhibit extreme elasticity with elastic recoveries as high as 85–90% (10 mN maximum load) attributed to the observed structure. However, the multilayers were stiffer and more elastic compared to that of the single-layers and thus shows promise for improved protective properties. 相似文献
20.
A design of a gradient bandgap Ti 1−xV xO 2 thin film electrode for wet-type solar cells is provided. The gradient bandgap film electrodes were prepared by heating stacked layers of varying V/Ti ratios using the sol-gel method. A composition gradient was observed for some of the samples by X-ray photoelectron spectroscopy although it was not very large. For the Ti 1−xV xO 2 film electrodes, conspicuous visible light photoresponse and photoelectrochemical stability were observed. The photocurrent increased with increasing bias potential. However, the photocurrent onset potentials of the Ti 1−xV xO 2 film electrodes were more positive than those of TiO 2 film electrodes, probably owing to the high surface state density introduced by the diffusion of vanadium ions. 相似文献
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