Epitaxial growth of CdS on CuInSe2

A single-source, vacuum vapor deposition technique was used to grow epitaxial (0001) CdS films on (112) CuInSe₂ single crystal substrates. Highly uniform single crystal CdS films up to 16 μm thick were produced and their quality assessed by x-ray diffraction, scanning electron microscopy, and electrical characterization.     

Epitaxial growth of AlN on single crystal Mo substrates

We have grown AlN films on single-crystalline Mo(110), (100), and (111) substrates using a low temperature pulsed laser deposition (PLD) growth technique and investigated their structural properties. Although c-axis oriented AlN films grow on Mo(100), the films contain 30° rotated domains due to the difference in the rotational symmetry between AlN(0001) and Mo(100). AlN films with only poor crystalline quality grow on Mo(111) substrates, probably due to the poor surface morphology and high reactivity of the substrates. On the other hand, single crystal AlN films grow epitaxially on Mo(110) substrates with an in-plane relationship of AlN[11-20] // Mo[001]. Reflection high-energy electron diffraction or electron backscattered diffraction analysis has revealed that neither in-plane 30° rotated domains nor cubic phase domains exist in the AlN films. X-ray reflectivity measurements have revealed that the heterointerface between AlN and Mo prepared by PLD at 450 °C is quite abrupt. These results indicate that PLD epitaxial growth of AlN on single crystal Mo substrates is quite promising for the fabrication of future high frequency filter devices.     

Epitaxial growth of PbTe on (100) GaAs substrates

The growth of PbTe films on GaAs by molecular beam epitaxy was studied by reflection high energy diffraction. The strains in the films were investigated by X-ray diffraction. Despite a lattice mismatch of 14.2%, oriented films can be grown up to a thickness of 4000 Å. For thicker films the thermal strain causes cracks if the samples are cooled from growth to liquid-nitrogen temperature.     

Epitaxial growth and structure of CdS films evaporated onto Ge

CdS evaporated in vacuum grew epitaxially at all substrate temperatures from 300 to 500° C on (100), (110) and (111) surfaces of germanium. On (100) substrates the CdS grew with the sphalerite structure in parallel orientation to the substrate. Films grown throughout the epitaxial range of temperature gave diffraction patterns that contained no satellite spots. They all contained 111 streaking, however. The films were therefore free of threedimensional defects but contained a high density of {111} planar defects. On the (110) substrates the CdS grew with the sphalerite structure in parallel orientation for substrate temperatures below about 370° C and the diffraction patterns of these films were free of satellite spots but contained 111 streaks of low intensity. In the diffraction patterns of the films grown above about 370° C doubling of the spots appeared and a domain structure was observed in the micrographs. This was due to the occurrence of a domain-form phase transformation of the sphalerite structure. On the (111) substrates the CdS grew with the wurtzite structure in (0001) orientation. No satellite spots or streaks appeared in the diffraction patterns of these films. Moiré fringes were seen in the micrographs of both (100) and (111) substrate specimens.     

Epitaxial and graphoepitaxial growth of materials on highly orientated PTFE substrates

The mechanism by which friction-deposited, highly orientated poly(tetrafluoroethylene) (PTFE) films promote orientated growth of materials was investigated. For this purpose, transmission electron microscopy was used to determine the orientation of polyethylene and 1,4-bis-2-(5-phenyloxazolyl)benzene (POPOP) crystals grown from the vapour phase onto the single crystal like PTFE films. Electron diffraction patterns revealed that the polyethylene crystals adopted an orientation that minimized the lattice mismatch at the interface between this material and the PTFE substrate. On the other hand, the POPOP crystals aligned in a fibre pattern, implying that orientated growth occurred because of the grating-shaped surface topography of the PTFE films. Evidently, the latter films were capable of promoting orientated growth of materials by a graphoepitaxial mechanism or conventional epitaxy, depending on the material used.     

Epitaxial growth of cadmium sulphide on (111) germanium substrates

Single-crystal expitaxial layers of CdS on (111) Ge substrates, 8 to 60 μm thick, have been grown from the vapour phase in a closed-tube system. Hydrogen was used as a transport agent. The experimental conditions (source and deposit temperatures, and initial pressure of hydrogen) have been defined where the growth of single-crystal expitaxial layers is feasible. Observations on the morphology of the layers are reported, which suggest that at least two different growth mechanisms should be active in the system. Finally, the composition of the gaseous phase was calculated by assuming a non-reactivity of the Ge substrate with the vapour phase.     

Epitaxial growth and reaction between Ag and SnTe substrates

The vacuum deposition of silver on thin film SnTe substrates at temperatures between 110 K and 620 K was studied by transmission electron microscopy and diffraction. It was found that at temperatures up to 370 K silver deposits grow in nearly perfect (001)[100]Ag//(001)[110]SnTe orientation. At higher substrate temperatures a topotactic exchange of Sn and Ag atoms between the substrate and deposit takes place leading to two perfectly oriented reaction products: Ag₂Te and Ag₃Sn. Their orientation relations were determined, and possible formation mechanisms are briefly discussed.     

Epitaxial growth on MgO on (001) surfaces of silver single-crystal film substrates

The epitaxial growth of evaporated MgO films (<25–4000 Å) on smooth (001) surfaces of silver single-crystal film substrates at a temperature inthe range 25°–200°C has been studied by reflection high energy electron diffraction. At substrate temperatures below 150°C, MgO is oriented with its (111) plane parallel to the surface of the substrate. The (111) orientation is fibrous. At 150°C a major fraction of the deposit is oriented in parallel and at 200°C only the parallel orientation is observed. The deposit initially grows as oriented three-dimensional nuclei. As the film thickness increases to 500 Å, randomly oriented MgO is simultaneously formed at the surface. With further increase in thickness the degree of epitaxial orientation decreases and at 1000 Å a small amount of one- degree (111) orientation appears at the surface. At 4000 Å the surface orientation becomes one-degree (111); the (111) orientation is interpreted as a final growth orientation.     

Si(111)衬底上6H-SiC薄膜的低压化学气相外延生长与表征

在Si(111)衬底上,采用SiH4-C3H8-H2气体反应体系,通过低压化学气相沉积(LPCVD)工艺外延出结晶质量良好的SiC薄膜.低温光致发光谱表明该薄膜属于6H-SiC多型体.X射线衍射图表明该薄膜具有高度的择优取向性.扫描电子显微镜图表明该薄膜由片状SiC晶粒组成.拉曼光谱和透射电子衍射谱的结果进一步表明该薄膜具有较高的结晶质量.对Si(111)衬底上6H-SiC薄膜的生长机制进行了初步探讨.     

Epitaxial growth of ZnO layers on (111) GaAs substrates by laser molecular beam epitaxy

ZnO layers were grown on (111) GaAs substrates by laser molecular epitaxy at substrate temperatures between 200 and 550 °C. X-ray diffraction analysis revealed that c-axis of ZnO epilayer with a wurtzite structure is perpendicular to the substrate surface. X-ray rocking curves and Raman spectroscopy showed that the crystal quality of ZnO epilayers depends on the substrate temperature during the growth. Strong near-band-edge emission in the UV region without any deep-level emissions was observed from the ZnO epilayers at room temperature. The results indicate that laser molecular beam epitaxy is a promising growth method for obtaining high-quality ZnO layers on (111) GaAs substrates.     

Epitaxial growth of thin gold films onto pure and doped NaCl and KCl substrates

The influence of impurities such as calcium, strontium or silver ions present in the substrates on the structural growth features of continuous gold thin films, vacuum evaporated at constant deposition rates onto NaCl and KCl substrates heated in the temperature range from 90 to 300 °C, was studied by transmission electron microscopy and transmission electron diffraction. The epitaxial growth of gold thin films is inhibited by the presence of 5 × 10^-1 mol.% strontium or calcium ions in the KCl and NaCl substrates. The presence of 1.7 × 10^-1 mol.% silver ions in the NaCl substrates enhances the epitaxial growth of the gold thin films even at a substrate temperature of 120 °C. An enhancement of the gold thin film epitaxial growth is also obtained with NaCl-2 × 10^-2mol.%Ag-5 × 10^-1mol.%Ca and NaCl-1.7 × 10^-1mol.%Ag-5 × 10^-1mol.%Ca substrates.     

Epitaxial growth of Cu(100) and Pt(100) thin films on perovskite substrates

Pulsed laser deposition has been used to grow epitaxially oriented thin films of Cu and Pt on (100)-oriented SrTiO₃ and LaAlO₃ substrates. X-ray diffraction results illustrated that purely epitaxial Cu(100) films could be obtained at temperatures as low as 100 °C on SrTiO₃ and 300 °C on LaAlO₃. In contrast, epitaxial (100)-oriented Pt films were attained on LaAlO₃(100) only when deposited at 600 °C. Atomic force microscopy images showed that films deposited at higher temperatures consisted of 3D islands and that flat, layered films were obtained at the lowest deposition temperatures. Importantly, Cu films deposited at 100 °C on SrTiO₃(100) were both purely (100)-oriented and morphologically flat. Pt and Cu films displaying both epitaxial growth and smooth surfaces could be obtained on LaAlO₃(100) only by using a three-step deposition process. High-resolution transmission electron microscopy demonstrated an atomically sharp Cu/SrTiO₃ interface. The crystalline and morphological features of Cu and Pt films are interpreted in terms of the thermodynamic and kinetic properties of these metals.     

Brush electrodeposited CdS films on low temperature substrates

Cadmium sulphide films were deposited by the brush plating technique on titanium and conducting glass substrates using a current density of 80 mA cm^− 2. X-ray diffraction studies indicated the polycrystalline nature of the films with hexagonal structure. As the deposition temperature decreased, the peaks were broad indicating the formation of nanocrystallites. Optical absorption measurements yielded band gap values in the range of 2.39-3.10 eV as the deposition temperature decreases. XPS studies confirmed the formation of CdS. Atomic force microscope studies indicated the roughness of the films decreases with the decrease of deposition temperature. The as deposited films were photoactive.     

Epitaxial growth of titanium oxide thin films on MgO(100) single-crystal substrates by reactive deposition methods

We synthesized titanium oxide thin films on MgO(100) single-crystal substrates by two reactive deposition methods and compared the structures of the thin films formed by these methods. In one method (pulsed-molecular-beam deposition method), molecular oxygen is supplied to the substrates by using a pulsed-molecular-oxygen beam source and deposition of one unit layer of titanium and subsequent supply of molecular oxygen are repeatedly performed. In the other method (radical beam deposition method), atomic oxygen is irradiated to the substrates by using an atomic oxygen beam generated by the radical beam source and irradiation of the atomic oxygen and deposition of titanium are simultaneously performed. In the case of the pulsed-molecular-beam deposition method, the crystal structure was changed by increasing the number of oxygen pulses supplied from the beam source. We found that the crystal structure of titanium oxide depended on the composition ratio of O:Ti in the film. The maximum ratio of O:Ti attainable by this method was 1.85, and at this ratio, (100)-oriented pseudorutile was formed. In the case of the radical beam deposition method, (100)-oriented anatase was formed below the titanium deposition rate of 0.10 nm/s and pseudorutile (TiO_2−δ) was formed above 0.15 nm/s. The pseudorutile structure synthesized on this experiment was very stable in air. We concluded that the crystal structure of the pseudorutile is a new crystal structure of titanium oxide.     

Epitaxial growth of Ag on Ag-doped NaCl

NaCl crystals doped with AgSO₄ have been grown in the laboratory and pure silver films of different thicknesses have been grown on the cleavages of doped and undoped crystals in a vacuum of the order of 10^-5 torr at room temperature by thermal evaporation. The films have been examined in an electron microscope and the nucleation and growth processes have been studied and compared. It is observed that: (i) preferential nucleation occurs on doped cleavages whereas uniform nucleation occurs on the undoped cleavages; (ii) coalescence of nuclei takes place earlier in films grown on doped substrates than on undoped ones; and (iii) films on doped substrates grow epitaxially with (100) orientation. The implications are discussed.     

Epitaxial growth of InP nanowires on germanium

The growth of III-V semiconductors on silicon would allow the integration of their superior (opto-)electronic properties with silicon technology. But fundamental issues such as lattice and thermal expansion mismatch and the formation of antiphase domains have prevented the epitaxial integration of III-V with group IV semiconductors. Here we demonstrate the principle of epitaxial growth of III-V nanowires on a group IV substrate. We have grown InP nanowires on germanium substrates by a vapour-liquid-solid method. Although the crystal lattice mismatch is large (3.7%), the as-grown wires are monocrystalline and virtually free of dislocations. X-ray diffraction unambiguously demonstrates the heteroepitaxial growth of the nanowires. In addition, we show that a low-resistance electrical contact can be obtained between the wires and the substrate.     

Epitaxial lead chalcogenide films: Orientation on substrates with the fluoride structure

Epitaxial films of the lead chalcogenides on (111)-oriented CaF₂, SrF₂ and BaF₂ substrates are azimuthally rotated by $\text{(2n ? 1)π}\text{3}$ relative to the substrate, e.g. (111)∥(111) but [10$\text{1}$]∥[$\text{1}$01]. It is shown that a model based on nearest and next-nearest neighbor interactions between the film and its substrate (over a sequence of five atomic (111) layers) leads to an interface structure that accounts for the experimentally observed orientation.