Pulsed laser deposition of titanium nitride and diamond-like carbon films on polymers

We have investigated the deposition of titanium nitride (TiN) and diamond-like carbon (DLC ) films on polymethylmethacrylate (PMMA) substrates using pulsed laser deposition (PLD) technique. The TiN and diamond-like films were deposited by laser ablation (KrF excimer laser λ = 248 nm, pulse duration τ～25 × 10^?9 s, energy density ～2?15J/cm²) of TiN and graphite targets, respectively, at room temperature. These films were characterized by transmission electron microscopy, scanning electron microscopy, x-ray diffraction, Auger electron spectroscopy, UV-visible absorption spectroscopy, and Raman spectroscopy. The TiN films were smooth and found to be polycrystalline with average grain size of 120Å. The diamond-like carbon films were amorphous with a characteristic Raman peak at 1550 cm^?1. The TiN films are highly adherent to the polymer substrates as compare to DLC films. The adhesion strength of DLC films on polymers was increased by interposing thin TiN layer (200Å) on polymers byin-situ pulsed laser deposition. The DLC films were found to be amorphous with good adhesion to TiN/PMMA substrates.     

调QNd:YAG脉冲激光在LiIO3中倍频的应力波

当调QNd:YAG脉冲激光通过LiIO3晶体时,由于晶体弱吸收激光而在其内激起应力波.在激光倍频时这种波得到增强,并随倍频的位相失配角变化.研究表明,这是因为激光倍频时部分1.064μm的基频激光转换成0.532μm的倍频光,并且LiIO3晶体吸收倍频光比吸收基频光更强.     

Microwave performance-property relationships of YBa2Cu3O7-δ thin films grown on LaAlO3 (001) substrate

We report correlations between growth parameters, structure and microwave performance for YBa₂Cu₃O7-δ (YBCO) thin films. Two series of YBCO thin films were grown byin-situ laser ablation. The first series were deposited at 100 mTorr oxygen pressure with a laser fluence of 2.9 Joule/cm², the second series were deposited at 600 mTorr of oxygen and a higher laser fluence of 5 Joule/cm². Microwave performance of these films was evaluated using a 5.6 GHz resonator. In both series, we found that films with higherT _c , narrower x-ray rocking curve width, and sharper electron channeling pattern tend to have higher microwave resonator Qs. Optimal film growth conditions were infered from this systematic study. Films grown at higher oxygen pressure have smoother surfaces and fewer second phases.     

ArF excimer laser induced CVD of aluminum oxide films

The authors have demonstrated photochemical deposition of aluminum oxides from Trimethylaluminum (TMA) and N₂O by using a pulsed ArF excimer laser (193 nm). Both TMA and N₂O are efficiently photodissociated by the 193 nm light. The films are grown on Si and InP wafers contained in a low pressure flowing cell with a heated substrate. The incident laser beam is focused and parallel to the substrate surface. Typical deposition rates are 80–150 A/min. Stripes of aluminum oxide 30 mm wide are uniformly grown on 7.5 cm Si-wafers. The film composition and purity have been investigated using Auger and Infra-red spectroscopy analysis. Surprising results are the relatively low concentration of carbon. Refractive index and thickness have been determined by an ellipsometer. Typical values for the films are 1.54–1.62. Metal-oxide-semiconductor capacitors have been fabricated and characterized. The C-V curves for n-InP/aluminum oxide have clockwise hysteresis, and minimum loop width is less than 0.5 V. The surface state densities are 1 × 10¹¹ cm^-2 eV⁻¹ at the mid band gap.     

脉冲激光沉积法沉积类金刚石薄膜的实验研究

为了研究脉冲激光沉积法中衬底温度和距离对类金刚石薄膜的影响,首先温度保持在200℃,靶和衬底间的距离分别取25.0mm和30.0mm来沉积类金刚石膜。其次温度保持在400℃,距离分别取25.0mm和30.0mm来沉积类金刚石膜。用Raman光谱仪对薄膜的微观结构进行检测,用原子力显微镜对薄膜的表面形貌进行检测。实验结果表明：距离增加或者温度升高都会导致类金刚石薄膜的密度和sp3/ sp2的比值减小,薄膜中石墨晶粒的数量增多和体积增大。近距离时温度的变化和低温时距离的变化对薄膜微观结构产生的影响更明显。距离和温度的变化对类金刚石薄膜的表面形貌也产生显著的影响。     

LD抽运Nd:YVO4/LBO腔内和频橙黄光连续激光器

报道了一种激光二极管抽运Nd:YVO4晶体、腔内Ⅰ类临界相位匹配LBO和频、连续波输出的全固态橙黄色激光器的设计和实验结果。橙黄色激光由Nd:YVO4晶体的1064nm和1342nm谱线腔内和频产生,输出波长为593.5nm。实验采用了双镜谐振腔结构,在1.6W的808nm注入抽运功率下,获得了最高功率为84mW连续波TEM00的橙黄色低噪声激光输出,光-光转换效率为5.3%,光束质量因子M21.2。实验和分析表明,采用激光二极管抽运Nd:YVO4晶体、LBOⅠ类临界相位匹配腔内和频是获得橙黄色激光的实用方法,并可以应用到Nd:YVO4晶体的其它谱线或具有多条谱线的其它激光增益介质,获得更多不同颜色的单谱线激光输出。     

脉冲Nd:YAG激光器选区晶化制备多晶硅薄膜

采用三倍频后的Nd:YAG固体脉冲激光系统(波长为355 nm)选区诱导晶化非晶硅薄膜,以制备多晶硅薄膜。分别测试了激光晶化前后薄膜的表面形貌和拉曼光谱。在文中分析了400 nm厚薄膜在激光扫描前后的表面形貌变化。拉曼光谱显示薄膜的晶化程度随着激光能量的增加而提高。最优的激光晶化能量密度与薄膜的厚度相关。对于300 nm和400 nm厚的非晶硅薄膜,有效晶化非晶硅的能量密度分别在440-634 mJ/cm²,777-993 mJ/cm²之间。在激光能量密度分别为634 mJ/cm²,975 mJ/cm²和1571 mJ/cm²时,300 nm、400 nm和500 nm厚薄膜达到最好的晶化效果。     

IR and UV laser-assisted deposition from titanium tetrachloride: A comparative study

Laser-induced TiCl₄ decomposition at vapour pressure was performed and comparative study of the composition and structure of thermally (at 10.6 μm) and photolytically (at 248 nm) deposited Ti-based films is presented. Emphasis was given to the less explored titanium deposition process by CO₂ laser pyrolysis of TiCl₄. The detailed structure of films deposited on quartz substrates was examined by scanning electron microscopy and X-ray photoelectron spectroscopy. The influence of the incident laser energy on the chemical content of the films as well as on the film growth rate was demonstrated. The results indicate that in the thermal IR decomposition of TiCl₄ a multilayer structure is formed with unsaturated TiSi_x at the interface and oxidized phases at the surface. The photolytic process leads to films with increased purity and a specific growth morphology.     

脉冲激光扫描淀积类金刚石薄膜

采用能量密度为1.178×109W/cm2的XeCl准分子激光直接辐照高纯度的石墨靶,并同时采用辅助放电,在1×10-5Torr的真空环境中,于温度为80℃的Si(100)的基片上淀积出类金刚石薄膜,Raman光谱显示在1330cm-1处出现较强的散射峰值;对薄膜红外光谱进行测试,其光谱在2900cm-1处有吸收峰,表明所淀积的类金刚石薄膜含有C-H键,其H元素与C元素的比为45%.薄膜的电阻率为1.89×106Ω/cm,通过光吸收测得的该薄膜的能隙为1.55eV.     

Integration of GaN thin films with dissimilar substrate materials by Pd-In metal bonding and laser lift-off

Gallium nitride (GaN) thin films grown on sapphire substrates were successfully bonded and transferred onto GaAs, Si, and polymer “receptor” substrates using a low-temperature Pd-In bond followed by a laser lift-off (LLO) process to remove the sapphire growth substrate. The GaN/sapphire structures were joined to the receptor substrate by pressure bonding a Pd-In bilayer coated GaN surface onto a Pd coated receptor substrate at a temperature of 200°C. X-ray diffraction showed that the intermetallic compound PdIn₃ had formed during the bonding process. LLO, using a single 600 mJ/cm², 38 ns KrF (248 nm) excimer laser pulse directed through the transparent sapphire substrate, followed by a low-temperature heat treatment, completed the transfer of the GaN onto the “receptor” substrate. Cross-sectional scanning electron microscopy and x-ray rocking curves showed that the film quality did not degrade significantly during the bonding and LLO process.     

Optimization of picosecond laser structuring for the monolithic serial interconnection of CIS solar cells

We report on the optimization of selective picosecond laser structuring for the monolithic serial interconnection of (Cu(In,Ga)(S,Se)₂) CIS thin film solar cells. We introduce a quantitative value to compare the energy efficiency of the different investigated laser processes, the specific ablation energy, which indicates the required energy to remove a certain volume of the specific material. We have examined the structuring efficiencies for induced laser ablation processes for a modification of the beam profile (elliptical and flat‐top beam shaping) and for the application of different laser wavelengths (1064 and 532 nm). Application of induced laser processes (often referred as “lift‐off”) decreases the specific ablation energy dramatically by nearly one order of magnitude. Modifications of the beam profile such as elliptical and flat‐top beam shaping are nearly halving the energy per ablated volume relative to a circular beam. The application of a laser wavelength 532 nm decreases the specific ablation energy compared with 1064 nm significantly for processes involving the CIS layer. We finally demonstrate that with a picosecond laser power of only 2 W, the molybdenum back contact (P1, glass side) and the ZnO front contact (P3, ZnO on CIS) can be structured with a process speed of up to 4 m/s. About 2 µm thick CIS layer (P2) is structured by standard direct laser ablation at higher energy densities with 200 mm/s. Copyright © 2012 John Wiley & Sons, Ltd.     

Pulsed laser deposition and physical properties of carbon nitride thin films

Carbon nitride thin films were grown using an approach that combines pulsed laser deposition and atomic beam techniques. The composition and phases of the carbon nitride materials obtained from the reaction of laser ablated carbon and atomic nitrogen have been systematically investigated. The nitrogen composition was found to increase to a limiting value of 50% as the fluence was decreased for laser ablation at both 532 and 248 nm. Analysis of these experiments show that the growth rate determines the overall nitrogen composition, and thus suggests that a key step in the growth mechanism involves a surface reaction between carbon and nitrogen. Infrared spectroscopy has also been used to assess the phases present in the carbon nitride thin films. This spectroscopic measurement indicates that a cyanogen-like impurity occurs in films with nitrogen compositions greater than 30%. Investigations of the effects of thermal annealing have been carried out, and show that the impurity phase can be eliminated to yield a single phase material. In addition, systematic measurements of the electrical resistivity and thermal conductivity of the carbon nitride films were made as a function of nitrogen content. The implications of these results are discussed.     

GaN从蓝宝石衬底上激光剥离技术的研究

通过激光剥离成功分离了 Ga N膜及其蓝宝石衬底。位于界面处的 Ga N吸收了波长 2 48nm的激光辐射 ,导致其热分解 ,产生 Ga和 N2 气。再将样品加热到 Ga的熔点 (2 9°C)以上 ,即可很方便地除去蓝宝石衬底。对于激光分离前后的 Ga N样品 ,进行了原子力显微镜 (AFM)和 X射线衍射实验 (XRD)的测量 ,证实了剥离过程并未改变 Ga N膜的质量。并进一步讨论了激光剥离的阈值能量密度和避免 Ga N膜破裂的几种方法。     

Growth of CsLiB6O10 thin films on Si substrate by pulsed laser deposition using SiO2 and CaF2 as buffer layers

CsLiB₆O₁₀ (CLBO) thin films are grown on Si (100) and (111) substrates using lower index SiO₂ and CaF₂ as buffer layers by pulsed KrF (248 nm) excimer laser ablation of stoichiometric CLBO targets over a temperature range of 425 to 725°C. A CaF₂ buffer layer is grown on Si by laser ablation while SiO₂ is prepared by standard thermal oxidation. From extended x-ray analysis, it is determined that CaF₂ is growth with preferred orientation on Si (100) at temperatures lower than 525°C while on Si (111) substrate, CaF₂ is grown epitaxially over the temperature range; this agrees well with observed reflection high energy electron diffraction patterns. X-ray 2θ-scans indicate that crystalline CLBO are grown on SiO₂/Si and CaF₂/Si (100). Analysis of reflectance spectra from CLBO/SiO₂/Si yields the absorption edge at 182 nm. Surface roughness of the CaF₂ and CLBO/CaF₂/Si film are 19 and 15 nm, respectively. This relatively rough surface caused by the ablation of wide bandgap CaF₂ and CLBO limits the application of CLBO for waveguiding measurement.     

脉冲激光沉积类金刚石膜技术

脉冲激光沉积(PLD)技术制备类金刚石(DLC)薄膜存在着金刚石相含量较低、石墨颗粒多、薄膜与衬底附着力差、膜内应力大等技术难题,为此,研究人员研究出了多种技术措施,如通过引入背景气体、超快激光、偏压、磁场以及加热等措施提高了薄膜金刚石相含量;采用金刚石或丙酮靶材、减小单脉冲能量等措施减少了石墨颗粒;采用间歇沉积、真空退火、超快激光等措施减少了膜内应力;合理没计过渡层改善了膜与衬底间的附着力等.这些技术有力地推动了脉冲激光沉积技术的发展.     

超快脉冲激光沉积类金刚石膜的研究进展

综述了脉冲沉积(PLD)类金刚石膜(DLC)的优势和局限,对其局限的补偿和突破,以及脉冲沉积法的重要发展方向——超快脉冲激光沉积(Ultra-fast PLD)类金刚石膜(DLC)的研究进展。     

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.     

利用金属键合和激光剥离技术制备GaN/metal /Si异质结构的研究

利用金属键合和激光剥离将生长在蓝宝石衬底上的GaN薄膜转移到Si衬底上。键合后采用波长为248nm的准分子脉冲激光辐照蓝宝石衬底,低温处理去除蓝宝石衬底。系统地研究不同键合温度和激光能量密度对GaN结构和光学特性的影响。AFM、XRD和PL测试表明：键合温度和激光剥离的能量密度较低,转移衬底后GaN的质量较好;激光剥离的阈值能量密度为300mJ/cm2;键合温度400℃的样品均方根粗糙度（RMS）约为50nm。     

GaN/metal/Si heterostructure fabricated by metal bonding and laser lift-off

A process methodology has been adopted to transfer GaN thin films grown on sapphire substrates to Si substrates using metal bonding and laser lift-off techniques. After bonding, a single KrF (248 nm) excimer laser pulse was directed through the transparent sapphire substrates followed by low-temperature heat treatment to remove the substrates. The influence of bonding temperature and energy density of the excimer laser on the structure and optical properties of GaN films were investigated systemically. Atomic force microscopy, X-ray diffraction and photolumi-nescence measurements showed that (1) the quality of the GaN film was higher at a lower bonding temperature and lower energy density; (2) the threshold of the energy density of the excimer laser lift-off GaN was 300 mJ/cm~2. The root-mean-square roughness of the transferred GaN surface was about 50 nm at a bonding temperature of 400 ℃.     

Formation and crystallization of silicon nanoclusters in SiN<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>:H films using femtosecond pulsed laser annealings

SiN _x :H films of different compositions grown on glass and silicon substrates using plasma-chemical vapor deposition at a temperature of 380°C have been subjected to pulsed laser annealings. The treatments are performed using titanium-sapphire laser radiation with a wavelength of 800 nm and a pulse duration of 30 fs. Structural changes in the films are studied using Raman spectroscopy. Amorphous silicon nanoclusters are detected in as-grown films with molar fractions of excess silicon of ∼1/5 and larger. Conditions required for pulsed crystallization of nanoclusters were determined. According to the Raman data, no silicon clusters were detected in as-grown films with a small amount of excess silicon (x > 1.25). Pulsed treatments resulted in the formation of silicon nanoclusters 1–2 nm in size in these films.