磁约束放电激励对N_2激光输出特性的影响

对磁约束放电激励技术在N2 激光器上的应用进行了实验研究。结果显示 ,横向磁场的引入可以大大提高N2 激光的输出 ,扩展工作气压范围 ,提高最佳工作气压值。     

直流放电辅助脉冲激光沉积Si基GaN薄膜的结构特征

采用直流放电辅助脉冲激光沉积技术,在Si(111)衬底上生长了Ga N薄膜.XRD、AFM、PL 和Hall测量的结果表明在2～2 0 Pa沉积气压范围内,提高沉积气压有利提高Ga N薄膜的结晶质量;在15 0～2 2 0 m J/ Pluse入射激光脉冲强度范围内,随着入射激光脉冲强度的提高,Ga N薄膜表面结构得到改善.研究发现,在70 0℃衬底温度、2 0 Pa的沉积气压和2 2 0 m J/ Pluse的入射激光脉冲强度的优化工艺条件下,所沉积生长的Ga N薄膜具有良好的结构质量和光电性能.     

缓冲气体对超辐射光抽运远红外激光器的影响

以NH3作为远红外激光的工作气体 ,以N2 作为缓冲气体 ,对加入缓冲气体前后的小型超辐射光抽运远红外激光器作理论比较研究。基于缓冲气体作用机理模型 ,计算出激光工作物质的综合弛豫时间 ;通过解半经典的密度矩阵方程 ,计算出远红外激光输出的频谱特性和工作气压。计算表明 ,加入缓冲气体后 ,远红外激光的输出得到提高 ;存在一个最佳混合气体比例 ,在这一比例下远红外激光输出达到最大 ;加入缓冲气体后 ,最佳工作气压比加入缓冲气体前获得提高。     

脉冲CO_2激光照射甲烷生成乙炔

本工作研究了脉冲 CO_2激光对甲烷的作用。得到了一定 CH_4气压下,单次照射后,C_2H_2相对产量与激光能量的关系。发现在一定气压下,能量为某一值时,能量利用率最高,并发现激光能遗在3 J附近时,C_2H_2产量与 CH_4气压成正比。     

单、双纵模腔式光泵远红外激光器的实验研究

实验上采用可选纵模的TEA－CO2激光器作泵浦源,用CO2－9R（16）线泵浦小型腔式NHG3远红外激光器,在单、双纵模泵浦条件下均获得波长为90．4μm的远红外谱线。对单、双纵模腔式光泵远红外激光的输出特性和工作气压作了实验比较研究,发现双纵模腔式光泵远红外激光可获得更强的远红外输出,具有较低的最佳工作气压值,并可在较宽的气压范围内工作。     

电子束泵浦KrF受激准分子激光器

本文报道了我国研制的第一台用高能电子束横向泵浦NF3、Kr和Ar混合物的KrF激光器。获得了2484(～3mJ)的激光输出。总工作气压从460托变到2660托均有激光输出。给出了KrF激光谱线、荧光谱线私激光光斑。还介绍了分气压不变时,激光光谱和激光输出功率随总气压变化的关系,中心波长随气压变化的关系,以及在固定气压下变化分气压比时,激光功率和激光光谱变化的情况。测得了中心波长随分气压比位移的实际值。研究了气体混合时间对出光的影响,以及多次泵浦对激光输出的影响。并在输出阈值、输出功率、激光和荧光谱线方面与国外同类型器件进行了比较。     

脉冲TEA CO2 激光器温度特性的理论分析

利用六温度模型速率方程计算了当激光工作气体温度从-30℃～+60℃变化时TEA CO2激光器输出脉冲能量的变化规律。结果表明,激光器输出脉冲能量随着工作温度的升高而近似线性下降;线性下降的快慢和激光工作气体组成、气压、输出耦合镜反射率、注入能量、工作气体组成等均有关系;工作气体气压越高、输出耦合镜反射率越大或注入能量越高,激光输出脉冲能量随温度升高而下降的速度越快。     

脉冲TEA CO_2激光器温度特性的理论分析

利用六温度模型速率方程计算了当激光工作气体温度从-30℃~ 60℃变化时TEACO2激光器输出脉冲能量的变化规律。结果表明,激光器输出脉冲能量随着工作温度的升高而近似线性下降;线性下降的快慢和激光工作气体组成、气压、输出耦合镜反射率、注入能量、工作气体组成等均有关系;工作气体气压越高、输出耦合镜反射率越大或注入能量越高,激光输出脉冲能量随温度升高而下降的速度越快。     

高频激励横流CO2激光器的实验研究

本文在实验上在气压为120mba、100mba和80mba,气压比为CO2:N2:Ar=7:46.5;46.5,间隙为20mm,26mm和27mm,电极直径为12mm、长为700mm的情况下,对网络的高频传输特性,间隙高频放电的伏安特性及激光功率输出特性进行了一定的研究,在国内首次得到高频激励横流CO2激光器400W的激光输出.注入功率密度达20W/cm3,与相同条件下的直流针板式激光器相比最大注入功率提高了约一倍,最大电光转换效率为9%.     

采用新型激励方式的长脉冲TE CO2激光器

从预电离的角度出发,对原有长脉冲TE CO2激光器的双高压开关抽运电路进行改进,设计了新型激励电路.在新激励电路中,加入一个合适大小的电感与激光器电极部分串联,为Pulser和Sustainer放电电路所共用.实验结果表明,改进电路能够增强预电离能力和增加激光脉冲能量.在一台增益体积1.17 L、气体混合比CO2:N 2:He=12.5:13、工作气压为40 kPa的TE CO2激光器中,改进电路比原来电路增加激光出达61%.文章给出了详细实验数据并作了简单理论分析.     

Nd:GdVO4晶体的生长与性能

报道了在N2+He(30%～50%Vol)气氛中用提拉法成功地生长了Nd:GdVO4晶体.激光实验中,LD泵浦功率为350mW,采用端泵方式获得波长为1060nm的激光输出,TEM00基模方式运行,阈值泵浦功率为95mW,输出功率为13mW,斜效率为5%.     

Carbon nanotubes grown from nickel catalyst pretreated with H2/N2 plasma

To find the possibility of using a low-temperature process in growing carbon nanotubes (CNTs), nickel catalyst converted from film into particles by microwave H₂/N₂ plasma and the following CNT growth are all kept at a low temperature of 250 °C. The flat panel display industry requests low-temperature rather than the traditional high-temperature process for CNT growth. It was found that H₂/N₂ proportion is very sensitive to nickel morphology and the subsequent CNT growth. Better nickel and CNTs morphology are obtained for the proportion H₂/N₂=3/1 than those for the generally used pure hydrogen environment. The process pressure selection during pretreatment can determine whether CNTs are grown or not. The diameter of growing CNTs is proportional to nickel particle size. Field emission results support field amplification coefficient claim. The long tube length and high tube density of growing CNTs demonstrate low threshold electric field. This work shows the potential to use H₂/N₂ instead of pure hydrogen plasma in growing qualified CNTs applied in display industry.     

N2 effect on GaAs etching at 150 mTorr capacitively-coupled Cl2/N2 plasma

The role of N₂ on GaAs etching at 150 mTorr capacitively-coupled Cl₂/N₂ plasma is reported. A catalytic effect of N₂ was found at 20-25% N₂ composition in the Cl₂/N₂ discharges. The peak intensities of the Cl₂/N₂ plasma were monitored with optical emission spectroscopy (OES). Both atomic Cl (725.66 nm) and atomic N (367.05 nm) were detected during the Cl₂/N₂ plasma etching. With the etch rate and OES results, we developed a simple model in order to explain the etch mechanism of GaAs in the high pressure capacitively-coupled Cl₂/N₂ plasma as a function of N₂ ratio. If the plasma chemistry condition became positive ion-deficient at low % N₂ or reactive chlorine-deficient at high % N₂ in the Cl₂/N₂ plasma, the GaAs etch rate is reduced. However, if the plasma had a more balanced ratio of Cl₂/N₂ (i.e. 20-25% N₂) in the plasma, much higher etch rates (up to 150 nm/min) than that in pure Cl₂ (50 nm/min) were produced due to synergetic effect of neutral chlorine adsorption and reaction, and positive ion bombardment. Pure Cl₂ etching produced 14 nm of RMS surface roughness of GaAs. Introduction of ?20% N₂ gas in Cl₂/N₂ discharges significantly reduced the surface roughness to 2-4 nm. SEM photos showed that the morphology of photoresist mask was strongly degraded. Etch rate of GaAs slightly increased from 10 to 40 nm/min when RIE chuck power changed from 10 to 150 W at 12 sccm Cl₂/8 sccm N₂ plasma condition. The surface roughness of GaAs etched at 12 sccm Cl₂/8 sccm N₂ plasma was 2-3 nm.     

Effects of annealing conditions on the properties of tantalum oxide films on silicon substrates

The formation of a SiO₂ layer at the Ta₂O₅/Si interface is observed by annealing in dry O₂ or N₂ and the thickness of this layer increases with an increase in annealing temperature. Leakage current of thin (less than 40 nm thick) Ta₂O₅ films decreases as the annealing temperature increases when annealed in dry O₂ or N₂. The dielectric constant vs annealing temperature curve shows a maximum peak at 750 or 800° C resulting from the crystallization of Ta₂O₅. The effect is larger in thicker Ta₂O₅ films. But the dielectric constant decreases when annealed at higher temperature due to the formation and growth of a SiO₂ layer at the interface. The flat band voltage and gate voltage instability as a function of annealing temperature can be explained in terms of the growth of interfacial SiO₂. The electrical properties of Ta₂O₅ as a function of annealing conditions do not depend on the fabrication method of Ta₂O₅ but strongly depend on the thickness of Ta₂O₅ layer.     

Low bias dry etching of III-nitrides in Cl2-based inductively coupled plasmas

Cl₂-based inductively coupled plasmas (ICP) with low additional dc self-biases (?100V) produce convenient etch rates (500–1500Å·min^?1) for III-nitride electronic device structures. A systematic study of the effects of additive gas (Ar, N₂, H₂), discharge composition, process pressure, and ICP source power and chuck power on etch rate and surface morphology has been performed. The general trends are to go through a maximum in etch rate with percent Cl₂ in the discharge for all three mixtures, and to have an increase (decrease) in etch rate with source power (pressure). Since the etching is strongly ion-assisted, anisotropic pattern transfer is readily achieved. Maximum etch selectivities of approximately six for InN over the other nitrides were obtained.     

The effect of hydrogen on boron diffusion in SiO2

The diffusivity of boron in silicon dioxide may be increased by the introduction of hydrogen into the annealing atmosphere. In this paper we report on the diffusion characteristics of boron ion-implanted into thermally grown SiO₂. A sensitive technique was used in which the boron atoms redistributed into the substrate are characterized by electrical methods. The diffusivity of boron in thermal SiO₂ was measured over the temperature range of 950-1150°C with hydrogen partial pressure from 0 to 0.2 atm. It was found that the diffusion coefficient of boron in oxide at 1150° C increases as the square root of the hydrogen partial pressure. At fixed pressure the temperature dependence of the diffusion coefficient obeys a single-activation-energy exponential rule. At 0.1 atm partial pressure of H₂ the activation energy is 3.0 eV and the preexponential factor is 6 x 10⁵ [cm²/sec.].     

Effects of Ball-Milling Atmosphere on the Thermoelectric Properties of TAGS-85 Compounds

Inspired by the high ZT value lately attained in Ar-protected ball-milled nanocrystalline p-BiSbTe bulk alloy, we report herein an investigation of the effects of ball-milling atmosphere on the thermoelectric (TE) properties of the traditional TE material (GeTe)₈₅(AgSbTe₂)₁₅ (TAGS-85). TAGS-85 samples were prepared via a melting–quenching–annealing process, and then ball-milled in different atmospheres and subsequently densified using a spark plasma sintering technique. The Seebeck coefficient, electrical conductivity, thermal conductivity, and Hall coefficient were measured as a function of temperature from 10 K to 310 K. It was found that different ball-milling atmospheres, i.e., air, liquid N₂ (LN₂), and Ar, profoundly affected the TE properties. A state-of-the-art figure of merit ZT ≈ 0.30 was attained at 310 K in the Ar-ball milled sample. The results are discussed in terms of the carrier concentration, mobility, crystallinity, and the grain boundary scattering.     

Optical absorption studies of Si implanted SiO2

Optical absorption of Si implanted SiO₂ is characterized as a function of implant dose and energy upon annealing in N₂, H₂ and O₂ ambients. Interpretation of optical data yields information regarding the structure of defects due to excess Si. These defects are responsible for the memory effect and enhanced conductivity previously reported for Si implanted SiO₂. A correlation between E-band absorption (Si-Si ‘wrong’ bond defect) intensity and the amount of excess Si was established. Annealing of this band in O₂ is diffusion-limited with a reaction cross-section of 5.10⁻¹⁵ cm². Compressive strain-induced, oxygen diffusivity-retardation was observed. The C-band absorption (relaxed oxygen vacancy defect) observed in this study is unique in its response to heat treatment in N₂ and H₂ since it does not anneal in these ambients. C-band annealing kinetics in O₂ closely parallel those of E-band. B₂-band absorption (unrelaxed oxygen vacancy defect) produced by Si implantation is very similar in its annealing properties to the published data.     

Superior suppression of gate current leakage in Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/Si<Subscript>3</Subscript>N<Subscript>4</Subscript> bilayer-based AlGaN/GaN insulated gate heterostructure field-effect transistors

AlGaN/GaN-based metal-insulator-semiconductor heterostructure field-effect transistors (MIS-HFETs) with Al₂O₃/Si₃N₄ bilayer as insulator have been investigated in detail, and compared with the conventional HFET and Si₃N₄-based MIS-HFET devices. Al₂O₃/Si₃N₄ bilayer-based MIS-HFETs exhibited much lower gate current leakage than conventional HFET and Si₃N₄-based MIS devices under reverse gate bias, and leakage as low as 1×10⁻¹¹ A/mm at −15 V has been achieved in Al₂O₃/Si₃N₄-based MIS devices. By using ultrathin Al₂O₃/Si₃N₄ bilayer, very high maximum transconductance of more than 180 mS/mm with ultra-low gate leakage has been obtained in the MIS-HFET device with gate length of 1.5 μm, a reduction less than 5% in maximum transconductance compared with the conventional HFET device. This value was much smaller than the more than 30% reduction in the Si₃N₄-based MIS device, due to the employment of ultra-thin bilayer with large dielectric constant and the large conduction band offset between Al₂O₃ and nitrides. This work demonstrates that Al₂O₃/Si₃N₄ bilayer insulator is a superior candidate for nitrides-based MIS-HFET devices.     

Integration of HfxTayN metal gate with SiO2 and HfOxNy gate dielectrics for MOS device applications

Interaction of Hf_xTa_yN metal gate with SiO₂ and HfO_xN_y gate dielectrics has been extensively studied. Metal-oxide-semiconductor (MOS) device formed with SiO₂ gate dielectric and Hf_xTa_yN metal gate shows satisfactory thermal stability. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) analysis results show that the diffusion depths of Hf and Ta are less significant in SiO₂ gate dielectric than that in HfO_xN_y. Compared to HfO_xN_y gate dielectric, SiO₂ shows better electrical properties, such as leakage current, hysteresis, interface trap density and stress-induced flat-band voltage shift. With an increase in post metallization annealing (PMA) temperature, the electrical characteristics of the MOS device with SiO₂ gate dielectric remain almost unchanged, indicating its superior thermal and electrical stability.