Waveguide properties of optical thin films grown by pulsed laser deposition

The propagation of optical beams in optical thin films grown by pulsed laser deposition is studied numerically in order to predict the influence of the film curvature on the performance of planar waveguide lasers. Several waveguiding structures are considered. The confinement of both the pump and the signal fields as well the overlap between the beams during propagation are examined.     

Epitaxial growth of nonpolar GaN films on r-plane sapphire substrates by pulsed laser deposition

Single-crystalline nonpolar GaN epitaxial films have been successfully grown on r-plane sapphire (Al₂O₃) substrates by pulsed laser deposition (PLD) with an in-plane epitaxial relationship of GaN[1-100]//Al₂O₃[11-20]. The properties of the ~500 nm-thick nonpolar GaN epitaxial films grown at temperatures ranging from 450 to 880 °C are studied in detail. It is revealed that the surface morphology, the crystalline quality, and the interfacial property of as-grown ~500 nm-thick nonpolar GaN epitaxial films are firstly improved and then decreased with the growth temperature changing from 450 to 880 °C. It shows an optimized result at the growth temperature of 850 °C, and the ~500 nm-thick nonpolar GaN epitaxial films grown at 850 °C show very smooth surface with a root-mean-square surface roughness of 5.5 nm and the best crystalline quality with the full-width at half-maximum values of X-ray rocking curves for GaN(11-20) and GaN(10-11) of 0.8° and 0.9°, respectively. Additionally, there is a 1.7 nm-thick interfacial layer existing between GaN epitaxial films and r-plane sapphire substrates. This work offers an effective approach for achieving single-crystalline nonpolar GaN epitaxial films for the fabrication of nonpolar GaN-based devices.     

Structural and magnetic study of hard-soft systems with ZnO barrier grown by pulsed laser deposition

Hard-soft systems with magnetic transition metal electrodes and ZnO barrier of variable thickness have been epitaxially grown by pulsed laser deposition on MgO(1 0 0) substrates. The structural reflection high-energy electron diffraction (RHEED) and X-ray diffraction (XRD) analysis have shown an epitaxial growth of the CoFe₂ bottom electrode, the permalloy top electrode and of the ZnO barrier. Magnetic measurements have shown a clear plateau with a separate reversal of both magnetizations of the top and bottom electrodes, which is promising for further tunnel magnetoresistance measurements. A ferromagnetic coupling between the magnetic electrodes through the barrier has been observed.     

PLD法生长Al2O3基ZnO薄膜的特性

在不同衬底温度下,用脉冲激光沉积法(PLD),在Al2O3(0001)平面上生长了ZnO薄膜。研究了衬底温度对其结晶质量、电学性质以及发光性质的影响。结果显示:XRD在2θ为34°处出现了唯一的ZnO(0002)衍射峰;ZnO薄膜的电阻率随衬底温度的升高而增大;在衬底温度为500℃时,出现了位于410nm附近的特殊的光致发光(PL)峰。     

A comparative study of pulsed laser deposition and flash evaporation of Culn0.75Ga0.25Se2 thin films

In this paper initial results are presented for the growth and characterisation of polycrystalline Culn_0.75Ga_0.25Se₂ thin films prepared by pulsed laser deposition and flash evaporation. Analogies are drawn between these two important deposition technologies. The deposited films were characterised using a veriety of analytical techniques, including energy-dispersive analysis of X-rays and Rutherford-backscattering spectroscopy for compositional evaluation, X-ray diffreaction and Raman spectroscopy for structural evaluation, scanning electron microscopy for surface examination and the four-point and hot-point probe techniques for electrical characterisation. The comparison of films produced by these two deposition methods revealed that, in terms of their stochiometry, electrical and physical characteristics, good-quality GIGS thin films could be produced by both techniques.     

Optical and electrical properties of epitaxial (Mg,Cd)xZn1−xO, ZnO, and ZnO:(Ga,Al) thin films on c-plane sapphire grown by pulsed laser deposition

A consistent set of epitaxial, n-type conducting ZnO thin films, nominally undoped, doped with Ga or Al, or alloyed with Mg or Cd, was grown by pulsed laser deposition (PLD) on single-crystalline c-plane sapphire (0 0 0 1) substrates, and characterized by Hall measurement, and UV/VIS optical transmission spectroscopy.The optical band gap of undoped ZnO films at nearly 3.28 eV was shifted by alloying with Mg up to 4.5 eV and by alloying with Cd down to 3.18 eV, dependent on the alloy composition. In addition, highly doped ZnO:Al films show a blue-shifted optical absorption edge due to filling of electronic states in the conduction band.The Hall transport data of the PLD (Mg,Zn,Cd)O:(Ga,Al) thin films span a carrier concentration range of six orders of magnitude from 3 × 10¹⁴ to 3 × 10²⁰ cm⁻³, which corresponds to a resistivity from 5 × 10⁻⁴ to 3 × 10³ Ω cm. Structurally optimized, nominally undoped ZnO films grown with ZnO nucleation and top layer reached an electron mobility of 155 cm²/V s (300 K), which is among the largest values reported for heteroepitaxial ZnO thin films so far.Finally, we succeeded in combining the low resistivity of ZnO:Ga and the band gap shift of MgZnO in MgZnO:Ga thin films. This results demonstrate the unique tunability of the optical and electrical properties of the ZnO-based wide-band gap material for future electronic devices.     

Study of magnetic impurity as defects in ZnO grown by pulsed laser deposition

The structural, electrical and magnetic properties of Zn_0.95Mn_0.05O films grown by a pulsed laser deposition system were studied. An X-ray diffraction was tried to verify a crystal structure of the sample. A capacitance-voltage measurement showed that the Zn_0.95Mn_0.05O has electrical properties of an n-type semiconductor, and its carrier concentration appears 5×10¹⁸ cm⁻³. From a deep level transient spectroscopy measurement, an oxygen vacancy and a Mn-related electron trap in the Zn_0.95Mn_0.05O films were appeared as E_c−0.62 eV and E_c−0.13 eV, respectively. A magnetic hysteresis of ferromagnetic was measured in the Zn_0.95Mn_0.05O at temperature of 15 K. The hydrogen plasma-annealed sample had larger magnetization than non-annealed sample because of interstitially located hydrogen atoms-mediated double exchange interaction.     

Ultra-short pulsed laser deposition and patterning of SiC thin films for MEMS fabrication

A Ti:Sapphire (IR 800-nm) femtosecond (fs) pulsed laser was used to ablate a sputtering grade of silicon carbide (SiC) in an ultra-high vacuum chamber. The laser-induced plasma species were then driven and grown to form 3C-SiC films of about 1 μm thick on single crystal silicon wafers at 20 °C (room temperature) and 500 °C. Scanning electron microscopy, atomic force microscopy, X-ray photoelectron microscopy, X-ray diffraction and nanoindentation were used to characterize the structure, composition, thickness and properties of the SiC films. Results of the femtosecond-pulse laser deposited (fs-PLD) films were compared with those obtained by atmospheric pressure chemical vapor deposition (APCVD) and nanosecond-pulse laser (excimer laser at 248-nm) deposition (ns-PLD). The distinctive features of fs-PLD films are their extremely smooth surfaces, stoichiometry, amorphous structure and low defect density compared to APCVD films, along with better film quality and higher growth rates than ns-PLD films. In addition to film growth studies, a SiC microgripper (to grab 20-μm-sized objects) was micromachined by use of the fs-pulsed laser to demonstrate the utility of ultra-short PLD in SiC-device fabrication.     

Room-temperature ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition

The ferromagnetic ordering in Mn-doped ZnO thin films grown by pulsed laser deposition (PLD) as a function of oxygen pressure and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700°C and 800°C under 10⁻¹ torr in oxygen pressure were found, whereas ferromagnetic ordering in the films grown under 10⁻³ torr disappeared at 300 K. The large positive magnetoresistance (MR), ∼10%, was observed at 5 K at low fields and small negative MR was observed at high fields, irrespective of oxygen pressure. In particular, anomalous Hall effect (AHE) in the Mn-doped ZnO film grown at 700°C under 10⁻¹ Torr has been observed up to 210 K. In this work, the observed AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.     

GaN薄膜制备及脉冲激光沉积法的研究进展

介绍了国内外制备GaN材料的历史和现状。分析了GaN材料及其薄膜的各种制备工艺的特点,并详细介绍了采用激光沉积工艺制备GaN薄膜的研究进展。     

衬底温度对PLD法制备的ZnO:Ga薄膜结构和性能的影响

利用脉冲激光沉积法在石英衬底上制备了镓掺杂氧化锌(ZnO:Ga)透明导电薄膜,研究了衬底温度对薄膜的结构、表面形貌和光电性能的影响.研究表明:制备的ZnO:Ga薄膜是具有六角纤锌矿结构的多晶薄膜.随着衬底温度的增加,衍射峰明显增强,晶粒尺寸增大.当衬底温度为450℃时,薄膜的最低电阻率为8.5×10<'-4>Ω·cm,...     

溅射和激光淀积的ZnO多晶薄膜的结构和发光性质

我们分别通过直流反应溅射及脉冲激光淀积法制备了ZnO多晶薄膜。X射线衍射结果显示出薄膜的c轴取向。原子力显微镜证实薄膜的多晶结构。两种方法制备的ZnO在光子激发下都发射较强的带边荧光。绿色荧光未被观察到。激光淀积在(001)硅表面的ZnO的发光源自“自由激子”辐射。激光淀积在(0001)氧化铝晶体表面的ZnO的发光机制则在相当宽的激发强度范围内都呈现出电子．空穴等离子体(electron-hole plasma)的复合特性。     

Current-voltage characteristics of p-Si/carbon junctions fabricated by pulsed laser deposition

Amorphous carbon/p-Si junctions were fabricated at different temperatures using KrF excimer laser (λ = 248 nm, pulsed duration 20 ns). The current-voltage measurements of the devices showed diode characteristics. The value of various junction parameters such as ideality factor, barrier height, and series resistance were determined from forward bias I-V characteristics, Cheung method, and Norde’s function. There was a good agreement between the diodes parameters obtained from these methods. The ideality factor of ∼1.12 and barrier height of ∼0.37 eV were estimated using current-voltage characteristics for films grown at room temperature.     

反应式脉冲激光溅射淀积AlN薄膜化学稳定性研究

就反应式脉冲激光溅射淀积制备氮化铝薄膜的过程，讨论了激光脉冲能量密度及脉冲频率对所有制备薄膜结构性能的影响，并对薄膜的化学稳定性作了比较详细的研究，结果表明，当薄膜中存在有未反应的单质铝时，薄膜的化学稳定性较差。比较而言具有高取向性，择优生长的致密ＡＩＮ微晶膜的化学稳定性优于结构相对疏松的非晶膜。     

脉冲激光沉积法制备ZnO基薄膜研究进展

作为一种新型的Ⅱ-Ⅵ半导体材料,ZnO具有优良的光学和电学性能,在紫外光发射器件、自旋功能器件、气体探测器、表面声波器件等领域有着广阔的应用前景.首先介绍了ZnO材料和脉冲激光溅射法的一些相关内容,然后从材料制备角度着重阐述了目前利用脉冲激光沉积法(PLD)制备ZnO基薄膜的若干重要研究方向,例如p型掺杂、p-n结的制备、Mg掺杂、Cd掺杂和磁性离子掺杂等.     

Effect of AlN buffer layer thickness on the properties of GaN films grown by pulsed laser deposition

The GaN films are grown by pulsed laser deposition (PLD) on sapphire, AlN(30 nm)/Al₂O₃ and AlN(150 nm)/Al₂O₃, respectively. The effect of AlN buffer layer thickness on the properties of GaN films grown by PLD is investigated systematically. The characterizations reveal that as AlN buffer layer thickness increases, the surface root-mean-square (RMS) roughness of GaN film decreases from 11.5 nm to 2.3 nm, while the FWHM value of GaN film rises up from 20.28 arcmin to 84.6 arcmin and then drops to 31.8 arcmin. These results are different from the GaN films deposited by metal organic chemical vapor deposition (MOCVD) with AlN buffer layers, which shows the improvement of crystalline qualities and surface morphologies with the thickening of AlN buffer layer. The mechanism of the effect of AlN buffer layer on the growth of GaN films by PLD is hence proposed.     

Electrospray deposition and characterization of cobalt oxide thin films

Cobalt oxide thin films were fabricated by means of electrospray deposition. The obtained films were characterized by Raman spectroscopy, X-ray diffraction and Scanning electron microscopy. The solution that was used gave the Co₃O₄ phase at different growth temperatures. The best granular surfaces were obtained at 250 °C as verified by all characterization techniques, while flaky surfaces were obtained at higher temperatures. The surface morphology is mostly granular except for high temperatures where the cobalt oxide is formed as flakes instead of grains.     

脉冲激光沉积法制备ITO薄膜及性质研究

本文采用脉冲激光沉积法(PLD)制备了ITO导电薄膜,并对其形貌、光学性质和电学性质进行了研究.结果表明,使用PLD方法制备的ITO导电薄膜在可见光区的平均透光率约为80%,方块电阻在100～200Ω/□之间.当衬底温度控制在300℃,氧压控制在1.33Pa时,可以得到具有较高透光率和电导率的ITO导电薄膜.