Growth of InN layers on Si (111) using ultra thin silicon nitride buffer layer by NPA-MBE

Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β-Si₃N₄ double buffer layer achieves minimum FWHM of E₂ (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~ 0.73-0.78 eV with a direct band nature. It is found that a double-buffer technique (InN/β-Si₃N₄) insures improved crystallinity, smooth surface and good optical properties.     

Preparation of single-crystal TiC (111) by radio frequency magnetron sputtering at low temperature

Single-crystal films of TiC (111) have been synthesized at room temperature on Al₂O₃ (0001) substrates by radio frequency magnetron sputtering using a compound Ti-C target. The substrate temperature and bias were varied to explore the influence of deposition parameters on the crystal structure. Both Al₂O₃ (0001) and Si (100) substrates were used for epitaxial growth of TiC films. A series of characterizations of TiC films were carried out, including Rutherford backscattering spectroscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. Single-crystal films of TiC (111) on the Al₂O₃ (0001) were demonstrated.     

Metalorganic chemical vapor deposition of Er2O3 thin films: Correlation between growth process and film properties

Er₂O₃ thin films have been grown by metalorganic chemical vapor deposition (MOCVD) at 600 °C on different substrates, including glass, Si (100) and sapphire (0001) using tris(isopropylcyclopentadienyl)erbium and O₂. The effects of growth parameters such as the substrate, the O₂ plasma activation and the temperature of organometallic precursor injection, on the nucleation/growth kinetics and, consequently, on film properties have been investigated. Specifically, very smooth (111)-oriented Er₂O₃ thin films (the root mean square roughness is 0.3 nm) are achieved on Si (100), α-Al₂O₃ (0001) and amorphous glass by MOCVD. Growth under O₂ remote plasma activation results in an increase in growth rate and in (100)-oriented Er₂O₃ films with high refractive index and transparency in the visible photon energy range.     

Tuning of electrical properties of InxOy thin films grown by MOCVD for different applications

Tuning of electrical properties of indium oxide (In₂O₃) films by means of metal organic chemical vapor deposition (MOCVD) is demonstrated. Body‐centered cubic In₂O₃ polycrystalline thin films on Al₂O₃(0001) substrates were obtained. The specific resistance of the as‐grown films can be tuned by about two orders of magnitude by varying the growth conditions.     

New buffer sublayers for heteroepitaxial III–V nitride films on sapphire substrates

It is suggested to deposit III–V nitride films onto sapphire substrates upon preliminary deposition of a buffer sublayer of a crystalline material with a cubic structure. It is shown experimentally that the deposition of a heteroepitaxial niobium sublayer onto a (0001)-oriented sapphire substrate or a niobium nitride sublayer onto a ( 11[`2]011\bar 20 )-oriented Al₂O₃ substrate eliminates a 30° rotation of the (0001)-oriented nitride film in the substrate plane. The elimination of this rotation provides considerable reduction of the lattice mismatch between the substrate and the nitride film, which, in turn, should increase the degree of crystal perfection of the film. In addition, the planes of semiconductor nitride films become parallel to the natural cleavage planes of the substrate. This fact provides for the possibility of manufacturing a heterolaser with a Fabry-Perot resonator, in which the role of the mirrors is played by natural cleavage planes of the film.     

Deposition of ZnO thin films on SiO2/Si substrate with Al2O3 buffer layer by radio frequency magnetron sputtering for high frequency surface acoustic wave devices

ZnO films with c-axis (0002) orientation have been grown on SiO₂/Si substrates with an Al₂O₃ buffer layer by radio frequency magnetron sputtering. Crystalline structures of the films were investigated by X-ray diffraction, atomic force microscopy and scanning electron microscopy. The center frequency of the surface acoustic wave (SAW) device with a 4.8 μm thick Al₂O₃ buffer layer was measured to be about 408 MHz, which was much higher than that (265 MHz) of ZnO/SiO₂/Si structure and approaches that (435 MHz) of ZnO/sapphire. It is a possible way as an alternative for the sapphire substrate for the high frequency SAW device applications, and is also useful to integrate the semiconductor and high frequency SAW devices on the same Si substrate.     

Fabrication of MgB2 Thin Film on Boride Substrates by Pulsed Laser Deposition

Superconducting MgB₂ thin films have been fabricated on originally prepared boride substrates (AlB₂ (0001), ZrB₂ (random orientation), CaB₆ (0001), Al₂O₃ (0001)) by pulsed laser deposition (PLD) at room temperature, followed by in-situ annealing process. The highest T _c of 30 K, transition width of 6 K was obtained for Al₂O₃ (0001). T _c s were lowered and no zero resistivity was observed for boride substrates.     

Amorphous carbon buffer layers for separating free gallium nitride films

The possibility of using amorphous diamond-like carbon (DLC) films for self-separation of gallium nitride (GaN) layers grown by hydride vapor-phase epitaxy has been analyzed. DLC films have been synthesized by plasma-enhanced chemical vapor deposition under low pressure on sapphire (Al₂O₃) substrates with a (0001) crystallographic orientation. The samples have been studied by the methods of Raman scattering and X-ray diffraction analysis. It is shown that thin DLC films affect only slightly the processes of nucleation and growth of gallium nitride films. Notably, the strength of the “GaN film–Al₂O₃” substrate interface decreases, which facilitates separation of the GaN layers.     

Oxidation study of polycrystalline InN film using in situ X-ray scattering and X-ray photoemission spectroscopy

Oxidation process of polycrystalline InN films were investigated using in situ X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS). The films were grown by dc sputter on sapphire (0001) substrates and were oxidized in air at elevated temperatures. The XRD data showed that the structure of the films changed to the bixbyite In₂O₃ (a = 10.11 Å) above 450 °C. Chemical configurations of the sample surfaces were investigated using high-resolution XPS. For the non-intentionally oxidized InN film, XPS analysis on the In 3d peak and the N 1s main peak at 396.4 eV suggests that indium and nitrogen are bound dominantly in the form of InN. An additional peak observed at 397.4 eV in the N 1s photoelectrons and the O 1s peaks indicate that the InN film surface is partly oxidized to have InO_xN_y configuration. After oxidation of the InN film at elevated temperature, the O 1s spectrum is dominated by In₂O₃ peak, which indicates that the structure is stable chemically with In₂O₃ configuration at least within the XPS probing depth of a few nm.     

Enhancement in High-Field J c Properties and the Flux Pinning Mechanism of MgB2 Thin Films on Crystalline SiC Buffer Layers

We have studied the influence of crystalline SiC buffer layers on the critical current density and on the flux pinning mechanism in MgB₂ thin films. Crystalline SiC buffer layers were deposited on the Al₂O₃ (0001) substrates by using a pulsed laser deposition method, and then MgB₂ thin films were grown on the SiC-buffered layer by using a hybrid physical-chemical vapor deposition technique. MgB₂ thin films with crystalline SiC-buffered layers showed a significant critical current density’s enhancement in the high magnetic field region. An uncommon plateau-like behavior was also observed when the normalized flux pinning force density was scaled with the reduced magnetic field. Based on the analyses of the scaling behavior of the flux pinning force, grain boundary pinning is likely to be a dominant pinning mechanism in the SiC-buffered MgB₂ thin films.     

Surface acoustic wave properties of aluminum oxide films on lithium niobate

Aluminum oxide (Al₂O₃) films have been deposited on lithium niobate (LiNbO₃) substrates by electron beam evaporation without any interlayer between them to ensure a good adhesion of the Al₂O₃ films to LiNbO₃ substrates. As Al₂O₃ thin films can sufficiently increase the surface acoustic wave (SAW) velocity, they can be used to improve the performance of the SAW device. The SAW phase velocity in the Al₂O₃/LiNbO₃ structure was found to increase with the insertion of an Al₂O₃ film, which can be attributed to the stiffening effect of the Al₂O₃ layer. The velocity change ratio of SAW was about 4.39% (at 304 MHz) for the Al₂O₃ (9.7 μm)/LiNbO₃ sample. A comparison with other findings in literature reveals that this result is better than what is available from diamond-like carbon/SiC buffer layer/LiNbO₃ structure, whose the velocity change ratio is 2%.     

Raman scattering and Rutherford backscattering studies on InN films grown by plasma-assisted molecular beam epitaxy

A series of InN thin films was grown on sapphire substrates via plasma-assisted molecular beam epitaxy (PA-MBE) with different nitrogen plasma power. Various characterization techniques, including Hall, photoluminescence, Raman scattering and Rutherford backscattering, have been employed to study these InN films. Good crystalline wurtzite structures have been identified for all PA-MBE grown InN films on sapphire substrate, which have narrower XRD wurtzite (0002) peaks, showed c-axis Raman scattering allowed longitudinal optical (LO) modes of A₁ and E₁ plus E₂ symmetry, and very weak backscattering forbidden transverse optical (TO) modes. The lower plasma power can lead to the lower carrier concentration, to have the InN film close to intrinsic material with the PL emission below 0.70 eV. With increasing the plasma power, high carrier concentration beyond 1 × 10²⁰ cm^− 3 can be obtained, keeping good crystalline perfection. Rutherford backscattering confirmed most of InN films keeping stoichiometrical In/N ratios and only with higher plasma power of 400 W leaded to obvious surface effect and interdiffusion between the substrate and InN film.     

The influence of porous silica substrate on the properties of alumina films studied by X-ray reflection spectroscopy

The structure of alumina (Al₂O₃) films of various thicknesses grown by the atomic layer deposition method on porous silica (por-SiO₂) substrates has been studied using soft X-ray reflection spectroscopy. It is established that the synthesized films are amorphous and that the ratio of Al atoms with tetrahedral and octahedral coordinations in a film depends on its thickness. It can be suggested that thicker Al₂O₃ films contain a greater proportion of Al atoms with tetrahedral coordination.     

Electroplating to visualize defects in Al2O3 thin films grown using atomic layer deposition

Thin films grown using atomic layer deposition (ALD) are known for being continuous and nearly pinhole-free. These characteristics enable ALD films to be important in many applications such as gas or copper diffusion barriers, gate dielectrics, surface modification and functionalization layers. Few methods have been demonstrated to characterize defects in ALD films. In this study, a method to render the defects visible in Al₂O₃ ALD thin films on conductive substrates has been developed by growing copper bumps locally at the defect sites using electroplating. The electroplated copper can be easily observed or inspected using conventional optical- or electron-microscopy. Using this approach, the defect density in Al₂O₃ ALD thin films grown on nickel substrates has been shown to be as low as 38 /cm².     

Properties of LiNbO3 based heterostructures grown by pulsed-laser deposition for optical waveguiding application

Epitaxial LiNbO₃ (LN) thin films have been grown onto (00.1) Al₂O₃ substrates and onto sapphire covered with a conductive ZnO buffer layer. For the two systems, the LN thin films are well crystallised and highly (00.1) oriented. Epitaxial relationships between the different layers are evidenced both on the LN/sapphire film and the LN/ZnO/sapphire heterostructure. The optical waveguiding propagation losses of the LN/sapphire films are very low (1 ± 0.5 dB/cm) while the LN/ZnO/sapphire heterostructure does not exhibit satisfying waveguiding properties mainly due to the high conductivity (600 S m^− 1) of the ZnO buffer layer.     

Reaction of CaAl<Subscript>4</Subscript>O<Subscript>7</Subscript> with (0001)-oriented α-Al<Subscript>2</Subscript>O<Subscript>3</Subscript>

Reactions between thin films of CA₂ and (0001)-oriented α-Al₂O₃ have been studied using a combination of microscopy techniques. Thin films of amorphous CA₂ were deposited on sapphire substrates by pulsed-laser deposition at 900 °C in an oxygen ambient atmosphere. After deposition, the reaction couples were heat treated in air for various times either at 1300 or 1400 °C. Atomic-force microscopy was used to monitor changes in the microstructure of the films. Interfaces between the different regions were examined by transmission electron microscopy (TEM) of cross-sectional samples prepared by focused ion-beam milling. The CA₂ films had dewetted the substrate surface as a result of the heat treatment. An interfacial reaction layer was observed between the dewetted CA₂ droplets and the substrate. The structure of this reaction layer was found to be consistent with γ-Al₂O₃ by computer analysis of high-resolution TEM images. There is a perfect epitaxy between the interfacial layer and the substrate. For the samples heat treated for longer times, hexagonal features were found on the substrate surface. The presence of these features on (0001)-oriented α-Al₂O₃ suggests that CA₆ platelets form by the transformation of the interfacial reaction layer. The results are discussed in relation to the crystallization behavior of the various calcium aluminate phases and the equilibrium-phase diagram of the CaO–Al₂O₃ system.     

Magnetic Resonance Studies of Half-Metallic Epitaxial CrO2 Thin Films Grown on Differently Oriented TiO2 Substrates

The results of structural and ferromagnetic resonance (FMR) investigations of epitaxial half- metallic chromium dioxide (CrO₂) thin films of thicknesses between 58?nm and 540?nm grown by chemical vapor deposition (CVD) on (100) and (110)-oriented TiO₂ single crystal substrates are presented. The angular dependences of the FMR spectra in different experimental geometries were obtained. Effective magnetic anisotropies of epitaxially grown CrO₂ films of different thicknesses on strain and strain-free surfaces of TiO₂ substrates were estimated. The results indicate that the magnetic behavior of the CrO₂ films results from a competition between the magnetocrystalline and strain anisotropies. It has been revealed that the strain anisotropy dominates in the films grown onto (100)-oriented TiO₂ substrates. On the contrary, the films grown onto (110)-oriented substrates demonstrate strain-free magnetic anisotropy behavior.     

Laser deposition of gallium nitride films

Insulating c-oriented hexagonal epitaxial gallium nitride (GaN) films have been obtained by means of pulsed laser sputtering of a gallium target in nonactivated nitrogen atmosphere. The GaN films were deposited onto (0001)-oriented sapphire substrates either directly or above a ZnO buffer layer. The laser-deposited films exhibit edge photoluminescence at 370 nm.     

Photoluminescence behaviors in ZnGa2O4 thin film phosphors deposited by a pulsed laser ablation

ZnGa₂O₄ thin film phosphors have been deposited using a pulsed laser deposition technique on Si (1 0 0) and Al₂O₃ (0 0 0 1) substrates at a substrate temperature of 550 °C with various oxygen pressures 100, 200 and 300 mTorr, and various substrate temperatures of 450, 550 and 650 °C with a fixed oxygen pressure of 100 mTorr. The films grown under different deposition conditions have been characterized using microstructural and luminescent measurements. Under the different substrate temperatures, ZnGa₂O₄ thin films show the different crystallinity and luminescent intensity. The crystallinity and photoluminescence (PL) of the ZnGa₂O₄ films are highly dependent on the deposition conditions, in particular, oxygen pressure, substrate temperature, a kind of substrates. The luminescent spectra show a broad band extending from 350 to 600 nm peaking at 460 nm. The PL brightness data obtained from the ZnGa₂O₄ films grown under optimized conditions have indicated that the sapphire is one of the most promised substrates for the growth of high quality ZnGa₂O₄ thin film phosphor.     

Self-assembled InN quantum dots grown on AlN/Si(111) and GaN/Al2O3(0001) by plasma-assisted molecular-beam epitaxy under Stranski–Krastanow mode

We demonstrate that InN quantum dots (QDs) can be spontaneously formed on AlN and GaN surfaces by plasma-assisted molecular-beam epitaxy under the Stranski–Krastanow (S–K) mode. Both Si(111) wafers and metal–organic chemical vapor deposition grown GaN/Al₂O₃(0001) templates were used as substrates in this work. Silicon is particularly interesting as a substrate for InN QD applications because of its electrical conductivity and transparency in the near-infrared. By using reflection high-energy electron diffraction (RHEED), the formation process of InN QDs can be monitored in situ. We observed the 2D–3D transition of S–K growth mode and the lattice constant varied dramatically at the 2D–3D transition point from AlN to InN lattice constant. Furthermore, from the ex situ atomic force microscopy and scanning electron microscopy measurements, we directly imaged InN QDs on the AlN surface with an average diameter of ∼ 14 nm and high areal density of ∼ 1.6 × 10¹¹ cm^− 2.