Effects of sapphire substrates surface treatment on epitaxial ZnO thin films grown by MOCVD

The surface treatment effects of sapphire substrate on the quality of epitaxial ZnO thin films grown by metal-organic chemical vapor deposition (MOCVD) were studied. The sapphire substrates have been investigated by means of atomic force microscopy (AFM) and X-ray diffraction rocking curves (XRCs). The results show that sapphire substrate surfaces have the best-quality by CMP with subsequent chemical etching. The surface treatment effects of sapphire substrate on the ZnO thin films were examined by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) measurements. Results show that the intensity of (002) diffraction peak of ZnO thin films on sapphire substrates treated by CMP with subsequent chemical etching is strongest. FWHM of (002) diffraction peak is narrowest and the intensity of UV peak of PL spectrum is strongest, indicating surface treatment on sapphire substrate preparation may improve ZnO thin films crystal quality and photoluminescent property.     

DNA immobilization and SAW response in ZnO nanotips grown on LiNbO3 substrates.

DNA immobilization enhancement is demonstrated in a structure consisting of ZnO nanotips on 128 degrees Y-cut LiNbO3. The ZnO nanotips are grown by metalorganic chemical vapor deposition (MOCVD) on the top of a SiO2 layer that is deposited and patterned on the LiNbO3 SAW delay path. The effects of ZnO nanotips on the SAW response are investigated. X-ray diffraction and scanning electron microscopy are used to analyze the ZnO nanotips, which are of single crystalline quality, and they are uniformly aligned with their c-axis perpendicular to the substrate surface. The photoluminescence (PL) spectrum of the ZnO nanotips shows strong near bandedge transition with insignificant deep level emission, confirming their good optical property. DNA immobilization enhancement is experimentally validated by radioactive labeling tests and SAW response changes. The ZnO nanotips enhance the DNA immobilization by a factor of 200 compared to ZnO film with flat surface. DNA hybridization with complementary and noncomplementary second strand DNA oligonucleotides is used to study the selective binding of the structure. This device structure possesses the advantages of both traditional SAW sensors and ZnO nanostructures.     

DNA immobilization and SAW response in ZnO nanotips grown on LiNbO/sub 3/ substrates

DNA immobilization enhancement is demonstrated in a structure consisting of ZnO nanotips on 128/spl deg/ Y-cut LiNbO/sub 3/.The ZnO nanotips are grown by metal-organic chemical vapor deposition (MOCVD) on the top of a SiO/sub 2/ layer that is deposited and patterned on the LiNbO/sub 3/ SAW delay path. The effects of ZnO nanotips on the SAW response are investigated. X-ray diffraction and scanning electron microscopy are used to analyze the ZnO nanotips, which are of single crystalline quality, and they are uniformly aligned with their c-axis perpendicular to the substrate surface. The photoluminescence (PL) spectrum of the ZnO nanotips shows strong near bandedge transition with insignificant deep level emission, confirming their good optical property. DNA immobilization enhancement is experimentally validated by radioactive labeling tests and SAW response changes. The ZnO nanotips enhance the DNA immobilization by a factor of 200 compared to ZnO film with flat surface. DNA hybridization with complementary and noncomplementary second strand DNA oligonucleotides is used to study the selective binding of the structure. This device structure possesses the advantages of both traditional SAW sensors and ZnO nanostructures.     

High quality epitaxial ZnO films grown on solid-phase crystallized buffer layers

High quality epitaxial ZnO films on sapphire (110) plane have been fabricated on ZnO homo-buffer layers crystallized via solid-phase epitaxially (SPE). The SPE-ZnO films are fabricated by annealing of amorphous ZnON (a-ZnON) films deposited by RF magnetron sputtering. During annealing, the a-ZnON films are oxidized and converted to ZnO crystal. X-ray diffraction (XRD) analysis shows that the resultant films are epitaxially grown on the sapphire substrates. By using the SPE-ZnO films as homo-buffer layers, the ZnO films with high crystallinity, which are deposited by RF magnetron sputtering, are fabricated. The full width at half-maximum of XRD patterns for 2θ-ω and ω scan of (002) plane are 0.094° and 0.12°, respectively, being significantly small compared with 0.24° and 0.55° for the films without buffer layers. Thus utilizing SPE buffer layers is very promising to obtain epitaxial ZnO films with high crystallinity.     

Sputtering ZnO films on langasite and its SAW properties

C-axis-oriented ZnO films were sputtered on Langasite substrate (LGS, La(3)Ga(5)SiO(14)). The crystalline structure of the films was determined by grazing incident angle X-ray diffraction, the surface microstructure of films was investigated by scanning electron microscopy and atomic force microscopy, the atom composition ratio O/Zn of films was determined by energy dispersive X-ray spectroscopy, and the resistivity of films was determined by the four-point probe instrument. The measurement results showed those films prepared were all polycrystalline hexagonal ZnO films. By analyzing the microstructure of the ZnO films, those prepared at the oxygen flow rate (O(2)/O(2)+Ar) of 20%, the RF power of 200 W, and the substrate temperature of 200 degrees C had the best performance: highly c-axis-oriented microstructures, dense surface morphology, and the atom composition ratio 1.02. The measured scattering parameters of the SAW device fabricated on the composite substrate (ZnO/LGS) with film thickness 1.76 microm showed an average shifted velocity around 2741 m/s at 57.1 MHz and a electromagnetic coupling coefficient greater than 1%.     

Analysis of SAW properties in ZnO/AlxGa1-xN/c-Al2O3 structures.

Piezoelectric thin films on high acoustic velocity nonpiezoelectric substrates, such as ZnO, AlN, or GaN deposited on diamond or sapphire substrates, are attractive for high frequency and low-loss surface acoustic wave devices. In this work, ZnO films are deposited on AlxGa1-xN/c-Al2O3 (0 < or = chi < or = 1) substrates using the radio frequency (RF) sputtering technique. In comparison with a single AlxGa1-xN layer deposited on c-Al2O3 with the same total film thickness, a ZnO/AlxGa1-xN/c-Al2O3 multilayer structure provides several advantages, including higher order wave modes with higher velocity and larger electromechanical coupling coefficient (K2). The surface acoustic wave (SAW) velocities and coupling coefficients of the ZnO/AlxGa1-xN/c-Al2O3 structure are tailored as a function of the Al mole percentage in AlxGa1-xN films, and as a function of the ZnO (h1) to AlxGa1-xN (h2) thickness ratio. It is found that a wide thickness-frequency product (hf) region in which coupling is close to its maximum value, K(2)max, can be obtained. The K(2)max of the second order wave mode (h1 = h2) is estimated to be 4.3% for ZnO/GaN/c-Al2O3, and 3.8% for ZnO/AlN/c-Al2O3. The bandwidth of second and third order wave modes, in which the coupling coefficient is within +/- 0.3% of K(2)max, is calculated to be 820 hf for ZnO/GaN/c-Al2O3, and 3620 hf for ZnO/AlN/c-Al2O3. Thus, the hf region in which the coupling coefficient is close to the maximum value broadens with increasing Al content, while K(2)max decreases slightly. When the thickness ratio of AlN to ZnO increases, the K(2)max and hf bandwidth of the second and third higher wave modes increases. The SAW test devices are fabricated and tested. The theoretical and experimental results of velocity dispersion in the ZnO/AlxGa1-xN/c-Al2O3 structures are found to be well matched.     

倾斜衬底沉积法在金属衬底上外延生长YBCO薄膜

YBa2Cu3O7-x(YBCO)镀膜导体在电力等能源领域有巨大应用前景.利用倾斜衬底沉积法在无织构的金属衬底上生长了MgO双轴织构的模板层,在这一模板层上实现了双轴织构的YBCO薄膜的外延生长.这些膜的双轴织构用X射线极图分析、φ-扫描作了测定,观测到了MgO[001]方向相对于衬底法线倾斜了31°.研究了不同缓冲层材料对YBCO外延生长的取向和双轴织构的影响,外延生长的高质量的YBCO薄膜的转变温度和临界电流密度分别达到了91K和5.5×105A/cm2的较高的值.     

ZnO nanostructures grown on epitaxial GaN

Presented is the growth of zinc oxide nanorod/nanowire arrays on gallium nitride epitaxial layers. A hierarchical zinc oxide morphology comprising of different scale zinc oxide nanostructures was observed. The first tier of the surface comprised of typical zinc oxide nanorods, with most bridging to adjacent nanorods. While the second tier comprised of smaller zinc oxide nanowires approximately 30 nm in width often growing atop the aforementioned bridges. Samples were analysed via scanning electron microscopy, as well as, cross-sectional and high resolution transmission electron microscopy to elucidate the detailed growth and structural elements of the heterostructure.     

Optical absorption in Gd3Ga5O12 epitaxial films grown from PbO-B2O3 based fluxed solution

We report the observation of additional optical absorption in single-crystal garnet films with the nominal composition Gd₃Ga₅O₁₂, grown by liquid-phase epitaxy from a supercooled fluxed solution based on PbO-B₂O₃. Pis’ma Zh. Tekh. Fiz. 25, 18–22 (September 12, 1999)     

Analysis of SAW propagation in gratings on ZnO/diamond substrates

The space harmonic method is used to analyze surface acoustic wave (SAW) propagation under an infinite periodic metal grating on ZnO/diamond composite layered substrates. Dispersion properties for shorted and open gratings are derived as a function of the thickness of the grating electrodes. From these dispersion relations, the coupling of modes (COM) parameters are derived. Energy profiles inside ZnO/diamond show that the energies contained in each of the ZnO and diamond layers are of the same order when the thickness of the ZnO layer is P/pi (P = grating period) and that the energy is contained within two wavelengths below the ZnO/diamond interface.     

Optical absorption of the Gd3Ga5O12 epitaxial films grown from Bi2O3-B2O3-CaO solution melt system

Single-crystalline garnet films with a stoichiometric composition of Gd₃Ga₅O₁₂ were grown for the first time by liquid phase epitaxy from a supercooled melt of the Bi₂O₃-B₂O₃-CaO solid solution system. The films exhibit no absorption bands in the visible spectral range.     

衬底和O2/Ar气体比例对ZnO薄膜结构及性能的影响

采用直流磁控溅射法沉积了ZnO薄膜,以X射线衍射(XRD)、扫描电镜(SEM)、原子力显微镜等手段对薄膜的晶体结构和微观相貌进行了分析,并对薄膜的电学性能进行了考察.结果表明:所制备薄膜沿c轴高度择优,并具有较高的电阻率;ZnO薄膜的沉积速率和c轴择优度是由O2/Ar气体比例和衬底共同决定的;Au衬底上的ZnO薄膜以三维生长为主,在Al和Si衬底上出现了不同程度的薄膜二维生长;电阻率随O2/Ar气体比例的提高逐渐增加,Si衬底上薄膜的电阻率高于Al和Au衬底上的.     

Electrical properties of Ta2O5 films deposited on ZnO

High dielectric constant (high-k) Ta₂O₅films have been deposited on ZnO/p-Si substrate by microwave plasma at 150°C. Structure and composition of the ZnO/p-Si films have been investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) for chemical composition. The electrical properties of the Ta₂O₅/ZnO/p-Si metal insulator semiconductor (MIS) structures were studied using high frequency capacitance-voltage (C-V), conductance-voltage (G-V) and current-voltage (I-V) characteristics. Charged trapping properties have been studied by measuring the gate voltage shift due to trapped charge generation under Fowler-Nordheim (F-N) constant current stressing.     

Luminescent properties of GaN-based epitaxial layers and heterostructures grown on porous SiC substrates

The photoluminescence of single epitaxial GaN layers and electroluminescence of double GaN/AlGaN heterostructures grown on porous silicon carbide (PSC) substrates was studied in comparison to the properties of analogous layers and structures grown on nonporous SiC substrates. The epilayers grown on PSC substrates are characterized by a lower concentration of dislocation-related nonradiative recombination centers. It is suggested that this factor favorably influences the radiative recombination processes in device structures based on group III nitride epilayers grown on PSC substrates.     

Structural and magnetic properties of FePd and CoPd alloy epitaxial thin films grown on MgO single-crystal substrates with different orientations

FePd and CoPd alloy thin films were prepared on MgO single-crystal substrates of (001)_B1, (110)_B1, and (111)_B1 orientations at 600 °C by ultra high vacuum rf magnetron sputtering. L1₀-FePd(001) films with the c-axis perpendicular to the substrate surface are obtained on MgO(001)_B1 substrates. FePd epitaxial films consisting of L1₀(110) and L1₀(011) crystals are formed on MgO(110)_B1 substrates. The c-axis of L1₀(110) crystal is parallel to the substrate surface, whereas that of L1₀(011) crystal is 44° canted from perpendicular direction. L1₀-FePd(111) films with the c-axis 54° canted from the perpendicular direction are formed on MgO(111)_B1 substrates. L1₀ ordering degree of these FePd films varies depending on the substrate orientation. On the other hand, disordered CoPd thin films of (001)_A1, (110)_A1, and (111)_A1 orientations epitaxially grow on MgO substrates of (001)_B1, (110)_B1, and (111)_B1 orientations, respectively. The magnetization properties of L1₀ ordered FePd and A1 disordered CoPd thin films are influenced by the crystal structure, the ordering degree, and the film orientation.     

Influence of O2 pressure on the properties of heavily-doped ZnO:Sb thin films grown by pulsed laser deposition

Heavily Sb-doped ZnO films were deposited on the glass substrates by pulsed laser deposition (PLD). X-ray diffraction (XRD) and photoelectron spectroscopy (XPS) were employed to characterize their microstructures and chemical valence states. Transmittance spectra and Hall measurements were used to evaluate their optical and electrical properties. It was found that the as-prepared ZnO:Sb thin films showed a single-hexagonal-phase structure, with the optical band gap tuning from 3.33 to 3.11 eV. The variation in the band gap was attributed to a large co-axis strain in the alloy films induced by Sb incorporation. Besides, the alloy films showed a semi-insulated characteristic with high resistivity of ~10⁴ Ω cm, which was possibly related to a compensation of intrinsic defects.