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.     

Synthesis and characterization of 4H-SiC on C-plane sapphire by C60 and Si molecular beam epitaxy

4H-SiC (silicon carbide) films were grown on (0001) sapphire substrate at rather low temperatures(1000-1100 °C) with relative high deposition rate by using fullerene (C₆₀) and silicon solid sources molecular beam epitaxy with substrate nitridation and aluminum nitride (AlN) buffer layer deposition prior to the SiC deposition. The effects of substrate nitridation and AlN buffer layer to the adhesion of the SiC thin films on sapphire have been studied. X-Ray diffraction, pole figure, atomic force microscope, Fourier transform infrared spectroscopy and photoluminescence were employed for the analysis of composition, orientation of the film and surface morphology. Relative high deposition rate at ∼ 165 nm/h was achieved.     

Improvement of InN layers deposited on Si(111) by RF sputtering using a low-growth-rate InN buffer layer

We investigate the influence of a low-growth-rate InN buffer layer on structural and optical properties of wurtzite nanocrystalline InN films deposited on Si(111) substrates by reactive radio-frequency sputtering. The deposition conditions of the InN buffer layer were optimized in terms of morphological and structural quality, leading to films with surface root-mean-square roughness of ~ 1 nm under low-growth-rate conditions (60 nm/h). The use of the developed InN buffer layer improves the crystalline quality of the subsequent InN thick films deposited at high growth rate (180 nm/h), as confirmed by the narrowing of X-ray diffraction peaks and the increase of the average grain size of the layers. This improvement of the structural quality is further confirmed by Raman scattering spectroscopy measurements. Room temperature PL emission peaking at ~ 1.58 eV is observed for InN samples grown with the developed buffer layer. The crystal and optical quality obtained for InN films grown on Si(111) using the low-growth-rate InN buffer layer become comparable to high-quality InN films deposited directly on GaN templates by RF sputtering.     

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.     

Effects of growth atmosphere and homo-buffer layer on properties of ZnO films prepared on Si(1 1 1) by PLD

ZnO films were synthesized on Si(1 1 1) substrates by pulsed laser deposition (PLD) under four different growth conditions. The structural and optical properties of the samples were characterized by reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and photoluminescence (PL) measurement. It is found that when ZnO film is directly prepared on Si, oxygen atmosphere can significantly enhance the near-band-edge (NBE) emission and decrease the deep-level (DL) emission, but cause a polycrystalline film. By introducing a homo-buffer layer fabricated at 500 °C in vacuum, epitaxial ZnO film with three-dimensional (3D) growth mode is achieved instead of the polycrystalline film. In particular, the epitaxial film with the buffer layer shows more intensive NBE emission and narrower full-width at half maximum (FWHM) of 98 meV than the film without the buffer layer. The experimental results suggest that both oxygen atmosphere and buffer layer are quite efficient during PLD to grow high-quality ZnO/Si heteroepitaxial films suitable for applications in optoelectronic devices.     

Epitaxial growth of anatase TiO2 thin films on LaAlO3(100) prepared using pulsed laser deposition

Titanium dioxide thin films were grown on a lattice-matched LaAlO₃(100) surfaces using pulsed laser deposition (PLD) in oxygen atmosphere. The films were characterized using X-ray diffraction (XRD), reflection high-energy electron diffraction (RHEED) and atomic force microscopy (AFM). The crystal structure of all the films was anatase. Preferred oriented films with a c-axis normal to the substrate surface were obtained. RHEED analysis also revealed that the films had the preferential in-plane orientation, demonstrating that anatase films were epitaxially grown on the substrate. The flatness of the films depended on their growth conditions and thickness.     

MOCVD growth of barium-strontium titanate films using newly developed barium and strontium precursors

We report on metal-organic chemical vapor deposition (MOCVD) of the Ba_xSr_1 − xTiO₃ (BST) films (with x ≈ 0.5) on SrTiO₃ substrates. This research comprises the development of new chemical precursors, modification of the MOCVD apparatus towards stoichiometric oxide growth and undesirable phase suppression, as well as establishing optimum growth conditions. The grown BST films were characterized by the set of experimental techniques, including high-resolution X-ray diffraction (HRXRD) and high-resolution scanning electron microscopy. The newly synthesized organo-metallic precursors exhibit better properties than the available precursors and, in particular, show low melting points of about 80 °C. By using these precursors, we succeeded to grow sub-micron thick BST films of high crystalline quality. Optimum growth temperature was found to be 740 °C. The symmetric and asymmetric HRXRD profiles, as well as wide-angle X-ray diffraction scans, taken from the films grown under optimal conditions, reveal epitaxial orientation relations between the film and the substrate.     

Structural and optical properties of GaN films grown on GaAs substrates by molecular beam epitaxy

GaN films are grown on [0 0 1] GaAs substrates by plasma-assisted molecular beam epitaxy using a three-step process that consists of a substrate nitridation, deposition of a low-temperature buffer layer, and a high-temperature overgrowth. X-ray diffraction and transmission electron microscopy indicate that this method promotes prismatic growth of c-oriented α-GaN. Photoluminescence studies show that the emission from cubic β-GaN inclusions dominates the spectrum.     

Low-temperature growth of highly c-oriented InN films on glass substrates with ECR-PEMOCVD

High quality InN films are deposited with an interlayer of high c-orientation (002) AZO (Aluminium-doped Zinc Oxide; ZnO:Al) films on glass substrates by electron cyclotron resonance plasma-enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) at low temperature. AZO films used as a buffer layer are effective for the epitaxial growth of InN films. The influence of Trimethyl Indium (TMIn) flux on the properties of InN films is systematically investigated by reflection high energy electron diffraction (RHEED), X-ray diffraction analysis (XRD), atomic force microscopy (AFM) and optical transmittance spectra. The results indicate that high quality InN films with high c-orientation and small surface roughness are successfully achieved at an optimized Trimethyl Indium (TMIn) flux of 5.5 sccm. The InN/AZO structures have great potential for the development of full spectra solar cells.     

Fabrication of epitaxial conductive LaNiO3 films on different substrates by pulsed laser ablation

LaNiO₃ (LNO) thin films were deposited on (1 0 0) MgO, SrTiO₃ (STO) and LaAlO₃ (LAO) crystal substrates by pulsed laser deposition (PLD) under 20 Pa oxygen pressure at different substrate temperatures from 450 to 750 °C. X-ray diffraction (XRD), ex situ reflection high energy electron diffraction (RHEED) and atomic force microscopy (AFM) were employed to characterize the crystal structure of LNO films. LNO films deposited on STO and LAO at a temperature range from 450 to 700 °C exhibit high (0 0 l) orientation. XRD ψ scans and RHEED observations indicate that LNO films could be epitaxially grown on these two substrates with cubic-on-cubic arrangement at a wide temperature range. LNO films deposited at 700 °C on MgO (1 0 0) substrate have the (l l 0) orientation, which was identified to be bicrystalline epitaxial growth. La₂NiO₄ phase appears in LNO films deposited at 750 °C on three substrates. The epitaxial LNO films were tested to be good metallic conductive layers by four-probe method.     

Texture effect of neodymium doped gallium oxide thin films on their optical properties

Neodymium doped β-Ga₂O₃ films were elaborated on (1 0 0) silicon and (0 0 0 1) sapphire substrates by the radiofrequency magnetron sputtering method. X-ray diffraction, transmission electron microscopy, spectroscopic ellipsometry and photoluminescence measurements were performed to characterize and compare layers elaborated on the two substrates. Also, the Nd content effects were investigated. Films prepared on sapphire substrates were found to form a close orientation relationship with the substrate (−2 0 1) β-Ga₂O₃ || (0 0 0 1) sapphire, whatever the Nd content in the matrix. By contrast, the films grown on silicon substrates lose this texture for high Nd concentrations with a concomitant decrease of the Nd ions luminescence.     

Transformation of c-oriented nanowall network to a flat morphology in GaN films on c-plane sapphire

The work significantly optimizes growth parameters for nanostructured and flat GaN film in the 480–830 °C temperature range. The growth of ordered, high quality GaN nanowall hexagonal honeycomb like network on c-plane sapphire under nitrogen rich (N/Ga ratio of 100) conditions at temperatures below 700 °C is demonstrated. The walls are c-oriented wurtzite structures 200 nm wide at base and taper to 10 nm at apex, manifesting electron confinement effects to tune optoelectronic properties. For substrate temperatures above 700 °C the nanowalls thicken to a flat morphology with a dislocation density of 10¹⁰/cm². The role of misfit dislocations in the GaN overlayer evolution is discussed in terms of growth kinetics being influenced by adatom diffusion, interactions and bonding at different temperatures. The GaN films are characterized by reflection high energy electron diffraction (RHEED), field emission scanning electron (FESEM), high resolution X-ray diffraction (HRXRD) and cathodoluminescence (CL).     

Structural properties and morphology of Zn(1 − x)CdxO solid solution grown on ZnO and C-plane sapphire substrate

Zn_(1 − x)Cd_xO solid solutions with a composition ranging from pure ZnO up to x = 0.062 have been grown on ZnO and c-plane sapphire substrates by using metal organic chemical vapor deposition. The optical transmission spectra were used to estimate the cadmium mole fraction of the solid solutions. The lattice deformation and morphology of these films were examined in detail using high resolution X-ray diffraction and atomic force microscopy as Cd incorporation and used substrate. Our study reveals significant lattice deformation from x ≥ 0.7%. The atomic force microscopy images show facetted grains for films grown on ZnO substrate but rather round for c-plane sapphire substrate. The grain shape is controlled by the presence of the ionic charges on the polar surface of ZnO which is disturbed by cadmium incorporation and also the employed substrate material.     

Depth dependence of structural quality in InN grown by metalorganic chemical vapor deposition

Rutherford backscattering and channeling is combined with X-ray diffraction to study the depth dependence of crystalline quality in InN layers grown by metalorganic chemical vapor deposition on sapphire substrate. The poorest crystalline quality in InN layer is produced at the intermediate region over 100 nm away from the InN/sapphire interface. With increasing layer thickness the crystalline quality improves to a certain degree dependent on the growth temperature. The InN sample grown at 450 °C is found to be more homogeneous than the sample grown at 550 °C. The difference in the defect profile is explained by the temperature-dependent growth modes. The inhomogeneity of structural quality and related properties such as carrier concentration and strain field is possibly the reason to observe a high energy wing in PL spectrum of the InN sample grown at 550 °C.     

A novel approach for codoping in ZnO by AlN

In the present work, we have illustrated a new idea of codoping in ZnO with AlN as codopant to achieve p-ZnO. ZnO films doped with different concentrations of AlN were grown by RF magnetron sputtering. The AlN doped ZnO (ANZO) films grown on sapphire substrate were subjected to X-ray diffraction (XRD), reflectance measurements, Hall measurements, atomic force microscopy (AFM) and energy dispersive spectroscopy (EDS) analysis. XRD analysis reveals that all films have grown in the form of hexagonal wurtzite structure with (002) preferential orientation. The FWHM of (002) peak decreases till 1 mol% of AlN and increases for further addition of AlN indicating the incorporation of more impurities (dopants). The reflectance measurements suggest that the reflectance decreases at lower concentration and increases above 1 mol% of AlN in the visible region ranging from 400 to 800 nm. Hall measurements show that all the films are n-type. The electron concentration increases initially and then decreases for further addition of AlN (>1 mol%) suggesting the incorporation of nitrogen into the film at higher concentrations of AlN. The presence of N in the films is further confirmed by EDS analysis. The rms surface roughness measured by AFM decreases exponentially with dopant concentration. The figure of merit increases upon codoping with AlN.     

Growth and characterization of non-polar ZnO thin films by pulsed laser deposition

Non-polar ZnO thin films were fabricated on r-plane sapphire substrates by pulsed laser deposition at various temperatures from 100 to 500 °C. The effects of the substrate temperature on structural, morphological and optical properties of the films were investigated. Based on the X-ray diffraction analysis, the ZnO thin films grown at 300, 400 and 500 °C exhibited the non-polar (a-plane) orientation and those deposited below 300 °C exhibited polar (c-plane) orientation. In the optical properties of non-polar ZnO films, there were two photoluminescence peaks detected. The peaks (near-band edge emission, blue emission) are due to electron transitions from band-to-band and shallow donor level to valence band, respectively.     

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.     

Influence of N2 flux on the improvement of highly c-oriented GaN films on diamond substrates

High-quality GaN films are deposited on freestanding thick diamond films by electron cyclotron resonance plasma-enhanced metal organic chemical vapour deposition (ECR-PEMOCVD). Trimethyl gallium (TMGa) and N₂ are applied as precursors and different N₂ fluxes are used to achieve high-quality GaN films. The influence of N₂ flux on the properties of GaN films is systematically investigated by X-ray diffraction analysis (XRD), reflection high energy electron diffraction (RHEED), atomic force microscopy (AFM) and Hall effect measurement (HL). The results show that the high-quality GaN films with small surface roughness of 4.5 nm and high c-orientation are successfully achieved at the optimized N₂ flux of 90 sccm. The most significant improvements in morphological, structural, and optical properties of GaN films are obtained by using a proper N₂ flux.     

Structural and optical properties of wurtzite InN grown on Si(111)

We report the structural and optical properties of InN films on Si(111) prepared by ion-beam-assisted filtered cathodic vacuum arc technique. X-ray diffraction and Raman spectroscopy measurements indicated that all the InN films were hexagonal crystalline InN. The InN films deposited at substrate temperature of 475 °C exhibited highly (0001) preferred orientation and texturing (cratered) surface morphology. The oxygen incorporated in the InN films was segregated in the form of amorphous indium oxide or oxynitride phases at the grain boundaries. Photoluminescence emission of ∼ 1.15 eV was observed at room temperature from the InN films.     

Effect of precursor on epitaxially grown of ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate by hydrothermal technique

Single crystalline ZnO thin film on p-GaN/sapphire (0 0 0 1) substrate, using two different precursors by hydrothermal route at a temperature of 90 °C were successfully grown. The effect of starting precursor on crystalline nature, surface morphology and optical emission of the films were studied. ZnO thin films were grown in aqueous solution of zinc acetate and zinc nitrate. X-ray diffraction analysis revealed that all the thin films were single crystalline in nature and exhibited wurtzite symmetry and c-axis orientation. The thin films obtained with zinc nitrate had a more pitted rough surface morphology compared to the film grown in zinc acetate. However the thickness of the films remained unaffected by the nature of the starting precursor. Sharp luminescence peaks were observed from the thin films almost at identical energies but deep level emission was slightly prominent for the thin film grown in zinc nitrate.