The refractive index measurements of RF magnetron sputtered ZnO thin film on sapphire

Measurements were made of the refractive index of an RF magnetron sputtered ZnO thin film on sapphire. We compare the experimental results to theory when TE and TM guided waves propagate in the plane at an arbitrary angle with respect to thecaxis when thecaxis lies in the plane of the film. Care also should be taken when one usesm-line spectroscopy to determine the refractive index of a film.     

Effect of V doping on initial growth of ZnO film on c-face sapphire substrate

The effects of the vanadium (V) doping on the initial growth of ZnO films on a c-face sapphire substrate were investigated. The V-doped ZnO (VZO) films were grown at 200 °C by RF magnetron sputtering with various V concentration ranges. The unit cell volume of the VZO films became larger than that of the ZnO films, but the grain size of the VZO films shrank with a smooth surface. It was also found that the V doping enhanced c-axis alignment at the initial growth in the range of about 10–40 nm thick. Furthermore, it can be considered that V atoms were located at the interstitial sites in the state of V3+ from an analysis of the chemical binding states. Therefore, considering the effect of the V doping on the improvement in rotational symmetry of in-plane orientation, epitaxial alignment to the sapphire substrate was enhanced by the interstitial V incorporation.     

Crack free ZnO thick film on sapphire substrate without GaN template grown by MVPE

A crack-free ZnO film with thickness of ∼65 μm is obtained on sapphire substrate without GaN template by metal vapor phase epitaxy. The residual stress is investigated in terms of thermal and non-thermal stress. Comparing the calculated values of the thermal stress with the experimental data of the non-thermal stress, it is shown that the non-thermal stress is much larger than the thermal stress. Annealing was used to reduce the non-thermal stress. A re-growth process was employed, using annealed ZnO sample as pseudo-substrate. The result indicates that the residual stress in annealed ZnO sample was reduced to half, and the critical thickness is improved to ∼70 μm in the ZnO film grown on annealed ZnO pseudo-substrate, compared with ∼15 μm for ZnO grown directly on sapphire substrate. In addition, crystal quality is greatly improved, determined by double-crystal X-ray diffraction.     

Strain status in ZnO film on sapphire substrate with a GaN buffer layer grown by metal-source vapor phase epitaxy

ZnO film of 8 μm thickness was grown on a sapphire (0 0 1) substrate with a GaN buffer layer by a novel growth technique called metal-source vapor phase epitaxy (MVPE). The surface of ZnO film measured by scanning electron microscope (SEM) is smooth and shows many regular hexagonal features. The full width at half maximum (FWHM) of ZnO(0 0 2) and (1 0 2) ω-scan rocking curves are 119 and 202 arcsec, corresponding a high crystal quality. The status of the strain in ZnO thick film was particularly analyzed by X-ray diffraction (XRD) ω-2θ scanning. The results show that the strain in ZnO film is compressive, which is also supported by Raman scattering spectroscopy. The compressive strain can solve the cracking problem in the quick growth of ZnO thick film.     

Porous MgO film grown on sapphire by pulsed-laser deposition

A porousMgO film was grown on sapphire by pulsed-laser deposition. First, small islands of ZnO are grown, and then MgO at a high temperature and high vacuum is deposited. The shortest distance between the two pores is about 5 um.The ZnO grains are grown at the bottom of the pore. The ZnO grains at the rim of the bottom are thinner than that of the centre at the bottom, at which the grains look like thin nano-rods. It is evident that MgO would not be deposited on ZnO small islands at a high vacuum and high temperature when the substrate is sapphire. This morphology can be used for fabricating the materials in which the shortest distance between the two nanoparticles is about 5 um. It seems that other porous materials can also be realised by this method.     

Microstructure and strain of ZnO molecular-beam epitaxial layers on sapphire

Strains and crystalline perfection of ZnO epitaxial layers on sapphire grown by molecular-beam epitaxy were studied using high-resolution X-ray diffrac tometry. The strain state of samples was determined by curvature measurements. The structural quality of layers was analyzed by diffraction measurements in the Bragg and Laue geometry using θ and (θ-2θ) scanning modes. It was found that the grown layers (Zn/O > 1) are subject to biaxial tensile stresses, while stresses are absent for Zn/O < 1. The density and depth of different dislocations were calculated from the diffraction peak broadening.     

CdTe电光调频晶体用于电光调Q研究

本文研究了CdTe电光调Q晶体及电光调频晶体的调制特性,报道了采用 CdTe电光调频晶体进行电光调 Q的光栅选支射频激励波导 CO2激光器,调 Q激光脉冲重复频率 1Hz～10 kHz可调,在 10 kHz重复频率时,获得激光脉冲峰值功率为 300 W,脉冲宽度为 150 ns.     

MBE growth and properties of ZnO on sapphire and SiC substrates

Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC substrates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a würtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O₂ into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 × 10¹⁸ cm⁻³ with an electron mobility of 260 cm²/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.     

Electro-optic diffraction grating for light beam modulation and diffraction

The interaction between a strong traveling microwave signal and an optical beam in an electro-optic material is described in the limit of very high microwave dielectric constant. The interaction produces effects analogous to those produced by a moving diffraction grating. When the optical beam is wider than the wavelength of the microwave signal, the first grating order is resolved from the zero-order or main beam. Under this condition two types of devices become possible: 1) a beam deflector which can position an optical maser beam on, for example, 10⁵distinct points with negligible crosstalk and with address times of order 10^-7s, 2) a baseband light intensity modulator which is founded on the fact that light deflected into the first-order beam by the microwave signal is removed from the main beam. The amount deflected into the first-order beam is proportional to the microwave power; the intensity modulation follows the microwave envelope. The power required for a given modulation depth is inversely proportional to the seven halfs power of the dielectric Constant. As an example, for a not unrealistic choice of dielectric constant of 10⁴, complete transfer from the zero-order to the first-order beam requires 5 watts of microwave power. The interaction length is of order one centimeter and the interaction bandwidth is essentially unlimited. As a baseband modulator the maximum instantaneous bandwidth is of order 10 percent of the subcarrier frequency. Experimental verification is provided in an earlier paper [1].     

A study of synthetic sapphire by photoluminescence and X-ray diffraction

We carry on with the topic described in our previous paper [Microelectron. J. 32 (2001) 955] in which Raman spectroscopy was employed to study synthetic sapphire. On a sample of α-Al₂O₃ which had served as a cryostat window and had been exposed to liquid nitrogen temperature for 2 years we measured three distinct types of Raman spectra in the wave number range 100-800 cm⁻¹. On the edge of the sample, a Raman spectrum was measured similar to that of the γ-phase of Al₂O₃. With intention to confirm or to rule out potential conversion of phases under the effect of low temperature we have performed photoluminescence and X-ray diffraction (XRD) studies of the sample. Photoluminescence analysis has revealed a qualitative difference of the edge of the sample as compared with other spots of the sapphire disc. XRD has confirmed high crystallographic quality of the sapphire sample under study, nevertheless, we have not managed to resolve crystallographic modifications.     

Catalyst-free growth of ZnO nanowires on various-oriented sapphire substrates by pulsed-laser deposition

Catalyst-free growth of one-dimensional zinc oxide (ZnO) nanowires is reported. ZnO nanowires were synthesized on ZnO buffer layers deposited on various-oriented sapphire substrates. Syntheses of ZnO buffer layers and nanowires were performed by ultraviolet pulsed-laser deposition. ZnO nanowire's number density was the lowest in the case of using m-cut sapphire substrates. ZnO nanowires grown on a-cut sapphire substrates had vertical alignment with distances of tens to hundreds of nanometers. On the other hand, ZnO nanowires grown on c-cut sapphire substrates had the biggest nucleation rate. The dependence of crystalline orientation of ZnO buffer layers on the orientation of sapphire substrates were investigated by electron back scatter diffraction measurement. From their results, the growth models of ZnO buffer layers were suggested and the variations in morphological properties of ZnO nanowires were discussed.     

Laser-beam modulation using grating diffraction effects

An alternative system for producing an electro-optic grating modulator is discussed. A polarisation grating is used to overcome electric-field reduction occurring with closely spaced electro-optic grating electrodes.     

Laser-beam modulation using grating diffraction effects

An optical-diffraction modulator, using an electro-optic crystal excited by a periodic array of metallic conductors, is described. The operation of the device is in some ways similar to that of an acoustoelectric modulator; it differs from it in that it has a bandwidth, potentially very wide, which extends from d.c. It may therefore find application as a baseband modulator.     

Low temperature Solution-Processed ZnO film on flexible substrate

Transparent conductive ZnO films were directly deposited on unseeded polyethersulfone (PES) substrates with a spin-spray method using aqueous solution at a low substrate temperature of 85 °C. All ZnO films were crystalline with wurtzite hexagonal structure and impurity phases were not detected. ZnO films deposited without citrate ions in the reaction solution had a rod array structure. In contrast, ZnO films deposited with citrate ions in the reaction solution had a continuous, dense structure. The transmittance of the ZnO films was improved from 11.9% to 85.3% as their structure changed from rod-like to continuous. After UV irradiation, the ZnO films with a continuous, dense structure had a low resistivity of 9.1×10⁻³ Ω cm, high carrier concentration of 2.7×10²⁰ cm⁻³ and mobility of 2.5 cm² V⁻¹ s⁻¹.     

Epitaxial growth of ZnO on GaN/sapphire substrate by radio-frequency magnetron sputtering

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization.     

利用磁控溅射在GaN/蓝宝石衬底上生长ZnO薄膜

Zinc oxide (ZnO) thin films were grown on n-GaN/sapphire substrates by radio-frequency (RF) magnetron sputtering. The films were grown at substrate temperatures ranging from 400 to 700 ℃ for 1 h at a RF power of 80 W in pure Ar gas ambient. The effect of the substrate temperature on the structural and optical properties of these films was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM) and photoluminescence (PL) spectra. XRD results indicated that ZnO films exhibited wurtzite symmetry and c-axis orientation when grown epitaxially on n-GaN/sapphire. The best crystalline quality of the ZnO film is obtained at a growth temperature of 600 ℃. AFM results indicate that the growth mode and degree of epitaxy strongly depend on the substrate temperature. In PL measurement, the intensity of ultraviolet emission increased initially with the rise of the substrate temperature, and then decreased with the temperature. The highest UV intensity is obtained for the film grown at 600 ℃ with best crystallization. oindent     

Investigation on doping behavior of copper in ZnO thin film

An experiment to determine the electronic and chemical states of Cu in a ZnO crystal was performed using Hall measurement, X-ray photoelectron spectroscopy (XPS) and low-temperature photoluminescence (PL). Cu atoms showed different behaviors in the ZnO matrix as a function of oxygen gas pressure. Metallic copper (Cu⁰)-related Cu 2p_3/2 peak was observed in highly n-type ZnO:Cu film deposited in 10 mTorr. In the Cu-doped p-type ZnO film prepared in 50 mTorr, Cu_Zn¹⁺-related peak and small Cu_Zn²⁺-related satellite peak exhibited and the optical acceptor binding energies of Cu3d⁹ and Cu3d¹⁰ were 173 and 213 meV, respectively.     

Laser diffraction from capillary waves on liquid film surfaces

A simple experiment for laser diffraction of capillary waves on liquid film surface (LFS) is realized. Steady and visible diffraction patterns are obtained. The dispersion relation of capillary waves on LFS is verified by laser diffraction. In particular, both the relation between the wave number and the film thickness at a fixed angular frequency and the relation between the angular frequency and the wave number at a fixed film thickness are investigated. The theoretical and experimental results are in good agreement.     

激光衍射法测量液体薄膜厚度的研究

为了测量厚度小于0.5mm不溶性液体薄膜的厚度,采用激光衍射法验证了液体薄膜的色散关系,并根据其机理,建立起一种实时、非接触的测量不溶性液体薄膜厚度的方法,测得了薄膜的厚度。结果表明,实验值与理论十分吻合。