表面预处理对SiO2/Si结构上APCVD生长SiC薄膜的影响

采用S iH4-C3H8-H2气体反应体系在S iO2/S i复合衬底上进行了S iC薄膜的APCVD生长。实验结果表明,H2表面预处理温度过高或时间过长会导致衬底表面S iO2层熔化再结晶或被腐蚀掉。通过“先硅化再碳化”的工艺方法可以较好地解决S iO2/S i复合衬底上S iC成核困难以及粘附性差的问题,同时还可以有效抑制S iO2中的O原子向S iC生长膜扩散。选择预处理温度和薄膜生长温度为1180℃、H2预处理、S iH4硅化和C3H8碳化时间均为30 s的最佳生长条件时,可以得到<111>晶向择优生长的多晶3C-S iC外延薄膜,薄膜生长速率约为2.0~2.5nm/m in.     

X-ray diffraction characterization of epitaxial CVD diamond films with natural and isotopically modified compositions

Comparative investigations of homoepitaxial diamond films with natural and modified isotopic compositions, grown by chemical vapor deposition (CVD) on type-Ib diamond substrates, are carried out using double-crystal X-ray diffractometry and topography. The lattice mismatch between the substrate and film is precisely measured. A decrease in the lattice constant on the order of (Δa/a)_relax ～ (1.1–1.2) × 10^–4 is recorded in isotopically modified ¹³С (99.96%) films. The critical thicknesses of pseudomorphic diamond films is calculated. A significant increase in the dislocation density due to the elastic stress relaxation is revealed by X-ray topography.     

离子轰击增强金刚石膜与Si衬底结合力的进一步研究

由于金刚石与Si有较大的表面能差,利用化学气相沉积(CVD)制备金刚石膜时,金刚石在镜面光滑的Si表面上成核困难,而负衬底偏压能够增强金刚石在镜面光滑Si表面上的成核,表明金刚石核与Si表面的结合力也得到增强.本文分析衬底负偏压引起的离子轰击对Si表面产生的影响之后,基于离子轰击使得Si衬底表面产生了微缺陷(凹坑)增大了金刚石膜与Si衬底结合的面积,理论研究了离子轰击对金刚石膜与Si衬底结合力的影响.     

Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

Advanced deposition phase diagrams for guiding Si:H-based multijunction solar cells

Phase diagrams have been established to describe very high frequency (vhf) plasma-enhanced chemical vapor deposition (PECVD) of intrinsic hydrogenated silicon (Si:H) and silicon–germanium alloy (Si_1?xGe_x:H) thin films on crystalline Si substrates that have been over-deposited with n-type amorphous Si:H (a-Si:H). The Si:H and Si_1?xGe_x:H films are prepared under conditions used for the top and middle i-layers of high efficiency triple-junction a-Si:H-based n–i–p solar cells. Identical n/i cell structures were co-deposited in this study on textured (stainless steel)/Ag/ZnO which serve as substrate/back-reflectors in order to relate the phase diagrams to the performance parameters of single-junction solar cells. This study has reaffirmed that the highest efficiencies for a-Si:H and a-Si_1?xGe_x:H solar cells are obtained when the i-layers are prepared under previously-described maximal H₂ dilution conditions.     

Bonding rearrangement in amorphous silicon nitrides deposited by hot-wire chemical vapor deposition upon thermal annealing

The bonding rearrangement upon thermal annealing of amorphous silicon nitride (a-SiN_x:H) films deposited by hot-wire chemical vapor deposition was studied. A wide range of N/Si atom ratio between 0.5 and 1.6 was obtained for the a-SiN_x:H sample series by varying the source gases ratio only. Evolutions of Si–N, Si–H and N–H bonds upon annealing were found to depend strongly on the N/Si atom ratio of the films. According to the above observations, we propose possible reaction pathways for bonding rearrangement in a-SiN_x:H with different N/Si ratios.     

Effect of the sign of misfit strain on the formation of a dislocation structure in SiGe epitaxial layers grown on Si and Ge substrates

Comparative analysis of the specific features of the formation of a dislocation structure in the single-layer epitaxial heterostructures Si_1?xGe_x/Si and Ge_1?ySi_y/Ge is performed. It is ascertained that, at a relatively low lattice mismatch between an epitaxial layer and a substrate, the sign of misfit strain at the interface significantly affects the processes of defect formation. The most probable reasons for the observed phenomena are analyzed with allowance for the specific features of the state of the ensemble of intrinsic point defects in epitaxial layers subjected to elastic strains of a different sign.     

Stoichiometry–structure correlation of epitaxial Ce1−xPrxO2−δ (x=0−1) thin films on Si(111)

Epitaxial oxide thin film layers are of interest for model catalytic studies. We report the growth of Ce_1?xPr_xO_2?δ mixed oxide layers of different stoichiometries (x=0–1) and oxygen deficiency (δ>0) on Si(111) by co-evaporating molecular beam epitaxy. The main objective is to identify the crystal phases and to investigate the correlation between compositions and crystal structures. X-ray photoemission spectroscopy was performed to quantify the stoichiometries. An extensive laboratory and synchrotron based X-ray diffraction analysis was carried out to determine the vertical and lateral lattice orientations and the strain status of the layers. The study revealed that single crystalline Ce_1?xPr_xO_2?δ/Si(111) heterostructures can be epitaxially grown on Si(111) for model catalytic studies. In addition to the structure–stoichiometry relationship typical to mixed oxide bulk powders, we identified a hexagonal mixed Ce–Pr oxide thin film phase not yet reported in bulk studies.     

Stacking pattern of multi-layer InAs quantum wires embedded in In0.53Ga0.47−xAlxAs matrix layers grown lattice-matched on InP substrate

Multi-layer InAs quantum wires were grown on, and embedded in In_0.53Ga_0.47−xAl_xAs (with x=0, 0.1, 0.3 and 0.48) barrier/spacer layers lattice matched to an InP substrate. Correlated stacking of the quantum wire arrays were observed with aluminum content of 0 and 0.1. The quantum wire stacks became anti-correlated as the aluminum content was increased to 0.3 and 0.48. The origin of such stacking pattern variation was investigated by finite element calculations of the chemical potential distribution for indium on the growth front surface of the capping spacer layer. It is shown that the stacking pattern transition is determined by the combined effect of strain and surface morphology on the growth front of the spacer layers.     

Si–Ge–Sn alloys: From growth to applications

In this review article, we address key material parameters as well as the fabrication and application of crystalline GeSn binary and SiGeSn ternary alloys. Here, the transition from an indirect to a fundamental direct bandgap material will be discussed. The main emphasis, however, is put on the Si–Ge–Sn epitaxy. The low solid solubility of α-Sn in Ge and Si of below 1 at.% along with the large lattice mismatch between α-Sn (6.489 Å) and Ge (5.646 Å) or Si (5.431 Å) of about 15% and 20%, respectively, requires non-equilibrium growth processes. The most commonly used approaches, i.e. molecular beam epitaxy (MBE) and chemical vapor deposition (CVD), will be reviewed in terms of crucial process parameters, structural as well as optical quality and employed precursor combinations including Germanium hydrides, Silicon hydrides and a variety of Sn compounds like SnD₄, SnCl₄ or C₆H₅SnD₃. Special attention is devoted to the growth temperature window and growth rates being the most important growth parameters concerning the substitutional incorporation of Sn atoms into the Ge diamond lattice. Furthermore, the mainly CVD-driven epitaxy of high quality SiGeSn ternary alloys, allowing the decoupling of band engineering and lattice constant, is presented. Since achieving fundamental direct bandgap Sn-based materials strongly depends on the applied strain within the epilayers, ways to control and modify the strain are shown, especially the plastic strain relaxation of (Si)GeSn layers grown on Ge.Based on recently achieved improvements of the crystalline quality, novel low power and high mobility GeSn electronic and photonic devices have been developed and are reviewed in this paper. The use of GeSn as optically active gain or channel material with its lower and potentially direct bandgap compared to fundamentally indirect Ge (0.66 eV) and Si (1.12 eV) provides a viable solution to overcome the obstacles in both fields photonics and electronics. Moreover, the epitaxial growth of Sn-based semiconductors using CMOS compatible substrates on the road toward a monolithically integrated and efficient group IV light emitter is presented.     

Magnetic Susceptibility and Peculiarities of Chemical Bond in the AgGa(S1‐xSex)2 Solid Solutions

The measurements of magnetic susceptibility of the AgGa(S_1‐xSe_x)₂solid solutions with the chalcopyrite structure have been performed and the lattice susceptibility separated into the Langevin diamagnetic and the Van Vleck paramagnetic terms. The obtained data were used to evaluate the character of chemical bond in these alloys. The correlations between the parameters of chemical bond and other physical properties are discussed. It is shown that the investigated solid solutions have preferably ionic character of chemical bond. The Ga‐S(Se) (B‐C) bonds are found to be stronger than the Ag‐S(Se) (A‐C) bonds.     

Metamorphic growth of tensile strained GaInP on GaAs substrate

Optical and structural properties of tensile strained graded Ga_xIn_1−xP buffers grown on GaAs substrate have been studied by photoluminescence, X-ray diffraction, atomic force microscopy, and scanning electron microscopy measurements. The Ga composition in the graded buffer layers was varied from x=0.51 (lattice matched to GaAs) to x=0.66 (1% lattice mismatch to GaAs). The optimal growth temperature for the graded buffer layer was found to be about 80–100 °C lower than that for the lattice matched GaInP growth. The photoluminescence intensity and surface smoothness of the Ga_0.66In_0.34P layer grown on top of the graded buffer were strongly enhanced by temperature optimization. The relaxation of tensile GaInP was found to be highly anisotropic. A 1.5 μm thick graded buffer led to a 92% average relaxation and a room temperature photoluminescence peak wavelength of 596 nm.     

Analysis of ambient gas influence on silicon layers crystallized by means of LPE

Epitaxial growth of thin layers from the liquid phase can occur with the use of solutions saturated under different ambient gases. Most often this process takes place in a vacuum or gaseous atmosphere of hydrogen or argon. As the experimental data show, the morphology of crystallized layers is determined by the ambient type in which the process occurs.The cohesion energy responsible for epitaxial lateral deposition processes on the substrate surface depends on the surface free energy which is a measure of attraction of the solution atoms by substrate atoms. In the case of crystallization of an epitaxial lateral layer of Si on a substrate partially masked with dielectric, the chemical potentials of atoms in the neighboring phases (determining the interface evolution) are not without influence on the relaxation velocity of the saturated liquid phase, and on the horizontal and vertical growth rate.The aim of the investigation was to analyze experimentally the influence of the ambient gases used during the LPE growth on the cohesion of the Sn–Si solution with substrates applied for the lateral epitaxial growth of Si layers. This work presents comparative temperature analysis of the wetting angle of such surfaces as Si, SiO₂ and SiN_x by the Sn–Si solution.     

Structure and properties of hydrogenated amorphous silicon carbide thin films deposited by PECVD

a-Si_1?xC_x:H films are deposited by RF plasma enhanced chemical vapor deposition (PECVD) at different RF powers with hydrogen-diluted silane and methane mixture as reactive gases. The structure and properties of the thin films are measured by infrared spectroscope (IR), Raman scattering spectroscope and ultra violet–visible transmission spectroscope (UV–vis), respectively. Results show that the optical band gap of the a-Si_1?xC_x:H thin films increases with increasing Si–C bond fraction. It can be easily controlled through controlling Si–C bond formed by modulating deposition power. At low deposition power, the bond configuration of the a-Si_1?xC_x:H thin film is more disordered owing to the distinct different bond lengths and bond strengths between Si and C atoms. At a too high deposition power, it becomes still high disordered due to dangling bonds appearing in the a-Si_1?xC_x:H thin film. The low disordered bond configuration appears in the thin film deposited with moderate deposition power density of about 2.5 W/cm².     

Thermodynamic analysis of vapor-phase epitaxial growth of GaAsN on Ge

In this paper, we use thermodynamic analysis to determine how the nitrogen (N) ratio in the source gases affects the solid composition of coherently grown GaAs_1?xN_x(x～0.03). The source gases for Ga, As, and N are trimethylgallium ((CH₃)₃Ga), arsine (AsH₃), and ammonia (NH₃), respectively. The growth occurs on a Ge substrate, and the analysis includes the stress from the substrate–crystal lattice mismatch. Calculation results indicate that to have just a few percent N incorporation into the grown solid, the V/III ratio in the source gases should be several thousands and the input-gas partial-pressure ratio NH₃/(NH₃+AsH₃) should exceed 0.99. We also find that the lattice mismatch stress from the Ge substrate increases the V/III source–gas ratio required for stable growth, whereas an increase in input Ga partial pressure ratio has the opposite effect.     

Triple axis diffractometric investigations of the microstructure of thin AlxGa1‐xN epitaxial films

Al_xGa_1‐xN/GaN (Si doped or undoped) with the Al content in the composition range of 0.046 ≤ x ≤ 0.164 grown on the c sapphire face by atmospheric pressure MOCVD method were studied by high resolution x‐ray diffraction including symmetrical and asymmetrical ω/2θ scans and reciprocal space maps. A high sensitivity to small inhomogeneities of the layer thickness and lattice mismatch between AlGaN and GaN is reported, recognised as changes in the interference pattern of the diffraction peak observed across the sample. They are very well correlated with optical properties derived from independent photoreflectivity measurements. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Low-temperature RPCVD of Si,SiGe alloy,and Si1−yCy films on Si substrates using trisilane (Silcore)

Si homo-epitaxial growth by low-temperature reduced pressure chemical vapor deposition (RPCVD) using trisilane (Si₃H₈) has been investigated. The CVD growth of Si films from trisilane and silane on Si substrates are compared at temperatures between 500 and 950 °C. It is demonstrated that trisilane efficiency increases versus silane's one as the surface temperature decreases. Si epilayers from trisilane, with low surface roughness, are achieved at 600 and 550 °C with a growth rate equal to 12.4 and 4.3 nm min⁻¹, respectively. It is also shown that Si_1−xGe_x layers can be deposited using trisilane chemistry.     

Defect passivation by hydrogen reincorporation for silicon quantum dots in SiC/SiOx hetero-superlattice

The SiC/SiO_x hetero-superlattice (HSL) consisting of alternating near-stoichiometric SiC barrier layers for the electrical transport and silicon rich SiO_x matrix layers for the quantum dot formation is a promising approach to the realization of silicon quantum dot (Si–QD) absorbers for 3rd generation solar cells. However, additional defect states are generated during post deposition annealing needed for the Si–QD formation causing an increase in sub-band gap absorption and a decrease in PL intensity. Proper passivation of excess defects is of major importance for both the optical and electrical properties of the SiC/SiO_x HSL Si–QD absorber. In this work, we investigate the effectiveness of the hydrogen reincorporation achieved with hydrogen plasma in a plasma-enhanced chemical vapor deposition (PECVD) reactor, hydrogen dissociation catalysis in hot-wire chemical vapor deposition (HWCVD) reactor and annealing in forming gas atmosphere (FGA). Both the HSL samples and single layer reference samples are tested. The passivation quality of the hydrogen reincorporation was examined by comparing electrical and optical properties measured after deposition, after annealing and after passivation. In addition, the formation of Si–QDs in SiC/SiO_x HSL was evaluated using high resolution transmission electron microscopy. We demonstrated that hydrogen can be successfully reincorporated into the annealed HSL sample and its single layer reference samples. FGA passivation is most effective for SiO_1.2 single layers and HSL samples. Passivation with PECVD appeared to be only effective for SiC single layers.     

Diamond film growth on the Mo–Re alloy foil

Nanocrystalline diamond film was deposited on the substrate of Mo–Re alloy foil by using a hot filament chemical vapor deposition (HFCVD) method. The morphology, band structures and crystalline structure of the film were analysed by scanning electron microscopy (SEM), Raman spectroscopy and X-ray diffractometer (XRD), respectively. The results show that the thickness of the diamond film is about 300 nm after 1 h deposition. There is a 2H-Mo₂C layer between the diamond film and the Mo–Re substrate. The values of a and the ratio c/a of Mo₂C are 3.003 and 1.579 Å, respectively. This Mo₂C layer might be formed due to carbon atoms in the gas phase diffusing into the Mo–Re alloy.     

Local lattice strains in the system of cubic Zn0.999Fe0.001S x Se1 − x (0 ≤ x ≤ 1) crystals

The structure of cubic Zn_0.999Fe_0.001S _x Se_{1 ? x} (0 ≤ x ≤ 1) crystals obtained by vapor-phase chemical transport has been investigated by thermal-neutron diffraction. The diffraction patterns of these crystals are found to exhibit previously unknown diffuse-scattering effects related to local static atomic displacements in the metastable fcc lattice. It is substantiated that the tendency to form polytypes, which is characteristic to a greater extent of zinc sulfide, can be a key factor of instability in the lattice of compounds belonging to the series of anion-substituted solid solutions under study.