基于室温脉冲量子级联激光器的脉内光谱技术研究

介绍了基于量子级联激光器的脉内光谱技术,一个长激发脉冲应用在中心波长为7.85 μm脉冲量子级联激光器上,用于快速波长扫描,通过分析比较不同工作参数下的激光光谱信号,寻求最佳的激光器工作参数,并且在选定的工作参数下对目标气体的吸收谱线进行测量,得到了中心在1273.7 cm-1的N2O 吸收谱线.     

基于量子级联激光器光腔衰荡光谱技术的痕量氨气检测

采用基于红外脉冲量子级联激光器的高灵敏光腔衰荡光谱(Cavity ring-down spectroscopy)技术建立了氨气在1027 cm-1(9.7 μm)附近的吸收光谱痕量检测实验装置.使用该装置对人体口腔呼出气体以及超净实验室环境中氨气成份进行了测量和分析,氨气的检测灵敏度达到10 ppb.模拟分析了激光器光谱线宽对测量结果和系统检测灵敏度的影响,随着激光器光谱线宽的增加,测量结果偏低,系统检测灵敏度下降.为了减小光源线宽对测量结果的影响,通过修正曲线对测量数据进行修正,得到了较好的结果.     

一种主被动激光雷达系统设计及应用

为综合利用激光雷达的光学接收天线,设计了一种可工作于主动状态和被动状态的光学遥感测量系统。处于主动状态时,主振荡激光器辐射1 064 nm 的激光脉冲,经倍频输出523 nm 激光,泵浦罗丹明染料,实现调谐脉冲输出,脉冲最高频率10 Hz,脉冲宽度为3. 0 ns,染料激光器输出脉冲能量可达105 mJ,主振荡输出激光脉冲可达1. 08 J。处于被动状态时,利用大气透过的太阳光谱,选取2 个波长的光谱线,采用比例光谱技术,根据激光雷达光学天线接收的太阳光谱强度,反演大气中反应性气体的柱浓度,再计算体积浓度。系统用于测量SO2 和O3 ,应用结果表明此系统的测量数据与国家相关测量平台数据非常吻合。     

可调谐二极管激光吸收光谱技术及其在大气质量监测中的应用

可调谐二极管激光吸收光谱(TDLAS)技术是利用二极管激光器的波长调谐特性,获得被选定的待测气体特征吸收线的吸收光谱,从而对污染气体进行定性或者定量分析.在大气痕量气体和气体泄漏的监测中,为了提高探测的灵敏度,一般会根据具体情况对激光器采取不同的调制技术如波长调制、振幅调制、频率或者位相调制等,同时和长光程吸收池相结合使用,并辅之以各种噪声压缩技术.TDLAS不仅精度较高,选择性强而且响应速度快,已经广泛用于大气中多种痕量气体的检测以及地面的痕量气体和气体泄漏的检测.报道了最近研制的一套可调谐二极管激光吸收光谱检测大气中甲烷浓度的实验装置,这套装置具有灵敏度高、检测限低(ppb量级)、易于集成为便携式痕量气体检测仪等优点,若激光器的调谐波长范围能覆盖1.3～1.8 μm或者在光路中装配几台窄范围可调谐激光器实现波长扫描范围覆盖1.3～1.8μm,则可同时实现对大气中诸多重要痕量气体如CO2、CH4、CO、CH2O、H2S、NH3、HCI、C2H2等的同步监测.     

脉冲式阵列量子级联激光器的气体检测仪

为了能够对多种混合气体进行精确的识别和浓度测量,根据被检测气体的红外光谱的吸收特性,利用阵列式量子级联激光器设计了高精度的气体检测仪。在激光器驱动电源的设计上采用了时分复用的方法,通过高速脉冲控制和分段拟合的方法实现了对电源输出的精准控制。同时,对红外探测器输出的微弱信号进行处理,大大提高了测量精度。测试结果表明：驱动电流的最大偏差仅为0.65 mA,稳定度优于4×10-5 A,并对四种气体在十个浓度等级上进行了测试,最大平均测量误差仅为0.80%。     

基于MOCVD生长的4.6 μm中红外量子级联激光器

中红外量子级联激光器在红外对抗、痕量气体检测、自由空间光通信等领域具有广阔的应用前景,采用MOCVD生长量子级联激光器的方法具有生产效率高、可做再生长、便于多组分生长等优点。报道了可室温连续波工作的中红外量子级联激光器,波长4.6 μm,采用MOCVD生长应变补偿的InGaAs/InAlAs材料。实验探究了不同掺杂对芯片性能的影响,通过优化掺杂浓度提升了器件性能。腔长3 mm,脊宽13 μm的芯片在288 K的温度下,脉冲模式下最大峰值功率达到722 mW,电光转换效率和阈值电流密度分别为6.3%和1.04 kA/cm2,在连续模式下功率输出达到364 mW。文中成功实现了用MOCVD生长中红外量子级联激光器,为中红外波段的激光应用提供了技术支撑。     

FTIR法测量中水汽吸收对测量精度影响的初步研究

水汽吸收线分布于整个中红外波段,它的存在干扰红外光谱的定量分析.分析了水汽谱吸收对测量精度的影响.利用傅里叶变换红外光谱法分别测量了经过干燥处理的待测气体和未经干燥处理的待测气体,并分别对两次测量中CO、CO2、N2O和CH4浓度的测量精度及检测限进行了比较.实验表明:对样气进行干燥预处理可以提高测量精度和检测限.     

基于量子级联激光器的气体检测研究

随着社会的发展,对基于激光光谱技术的快速、灵敏和选择性气体探测的需求日益增加,量子级联(QC)激光器特有的高输出功率、宽调谐范围和能够在室温或者接近室温下工作的特性使它成为气体遥测的理想光源.详细描述了QC激光器,介绍了基于室温脉冲QC-DFB激光器的典型的中红外激光光谱实验装置,并探讨了QC激光器应用于气体检测的广阔前景.     

非链式脉冲氟化氘激光器光谱特性

为了探索氟化氘(DF)激光器级联效应及工作气体参数对激光光谱的影响,对自引发放电非链式脉冲DF激光器进行了光谱特性测试。采用DF激光谱线分析仪和Hg Cd Te光电探测器测试了P3(7)→P2(8)→P1(9)光谱脉冲波形,发现P1(9)支谱线率先实现振荡输出,脉冲前沿延迟80~100 ns后P2(8)、P3(7)两条谱线依次输出。在不同工作气体配比及总气压条件下测试了DF激光输出谱线条数及各谱线间相对能量,在3.5~4.2μm光谱范围内测得了22条激光跃迁谱线,且总气压为8.1 k Pa,工作气体(SF6和D2)气压配比为6:1时,具有量子级联效应的P3(8)→P2(9)→P1(10)光谱串能量占总输出能量的25.9%。结果表明,多谱线DF激光器能级间存在量子级联效应,通过优化工作气体参数可有效提升级联谱线输出时增益提取效率。     

中远红外量子级联激光器研究进展(特邀)

量子级联激光器具有效率高、体积小、功耗低、波长可大范围选取的特点,已经被广泛应用于定向红外对抗系统、自由空间光通信和痕量气体传感等领域。回顾了量子级联激光器近20年的进展。首先总结了量子级联激光器的总体发展历程和发光原理;接着介绍了主要用于定向红外对抗的大功率量子级联激光器的几种典型有源区结构设计,然后讨论了气体传感用的单模分布反馈量子级联激光器;接着又论述了单片集成高亮度量子级联激光器相干阵列的研究情况;此外,还介绍了自由空间通信用的量子级联激光器的发展情况;最后,描述了近些年才出现中红外量子级联激光器光频梳的研究进展。     

Effects of wet N2O oxidation on interface properties of6H-SiC MOS capacitors

Oxynitrides were grown on n- and p-type 6H-SiC by wet N₂O oxidation (bubbling N₂O gas through deionized water at 95°C) or dry N₂O oxidation followed by wet N₂O oxidation. Their oxide/SiC interfaces were investigated for fresh and stressed devices. It was found that both processes improve p-SiC/oxide but deteriorate n-SiC/oxide interface properties when compared to dry N₂O oxidation alone. The involved mechanism could be enhanced removal of unwanted carbon compounds near the interface due to the wet ambient, and hence a reduction of donor-like interface states for the p-type devices. As for the n-type devices, incorporation of hydrogen-related species near the interface under the wet ambient increases acceptor-like interface states. In summary, wet N ₂O oxidation can be used for providing comparable reliability for nand p-SiC MOS devices, and especially for obtaining high-quality oxide-SiC interfaces in p-type MOS devices     

Studies of CW lasing action in CO2-CO,N2O-CO, CO2-H2O, and N2O-H2O mixtures pumped by blackbody radiation

A proof of principle experiment to evaluate the efficacy of CO and H₂O in increasing the power output for N₂O and CO ₂ lasing mixtures has been conducted and theoretically analyzed for a blackbody radiation-pumped laser. The results for N₂ O-CO, CO₂-CO, N₂O-H₂O and CO₂-H₂O mixtures are presented. Additions of CO to the N₂O lasant increased power up to 28% for N₂O laser mixtures, whereas additions of CO to the CO₂ lasant, and the addition of H₂O to both the CO₂ and N₂O lasants, resulted in decreased output power     

High quality gate dielectrics grown by rapid thermal processingusing split-N2O technique onstrained-Si0.91Ge0.09 films

Thermal stability and strain relaxation temperature of strained Si _0.91Ge_0.09 layers has been investigated using double crystal x-ray diffraction (DCXRD). High quality gate oxynitride layers rapid thermally grown on strained Si_0.91Ge_0.09 using N₂O and the split N₂O cycle technique below the strained relaxed temperature is reported. A positive fixed oxide charge density was observed for N₂O and split-N₂ O grown films. The O₂ grown films exhibit a negative fixed oxide charge. The excellent improvements in the leakage current, breakdown field and charge-to-breakdown value of the N₂O or split-N₂O grown films were achieved compared to pure O₂ grown films     

Reduction of RIE-damage by N2O-anneal of thermal gateoxide

We have investigated RIE-induced damage in MOS devices with thermal oxide as well as N₂O-annealed oxide as gate dielectrics. A systematic improvement in robustness against RIE-induced damage is seen when N₂O flow rate and/or N₂O anneal temperature are increased. We have demonstrated a N₂O anneal process at 900°C, which provides a robust SiO₂/Si interface against plasma damage and hot carrier stress     

High-field-induced leakage in ultrathin N2O oxides

Stress-induced leakage current (SILC) is studied in ultrathin (~50 Å) gate oxides grown in N₂O or O₂ ambient, using rapid thermal processing (N₂O oxide or control oxide, respectively). MOS capacitors with N₂O oxides exhibit much suppressed SILC compared to the control oxide for successive ramp-up, constant voltage DC, and AC (bipolar and unipolar) stresses. The mechanism for SILC is discussed, and the suppressed SILC in N₂O oxide is attributed to suppressed interface state generation due to nitrogen incorporation at the Si/SUO₂ interface during N₂O oxidation     

A novel technique of N2O-treatment onNH3-nitrided oxide as gate dielectric for nMOS transistors

A novel technique of N₂O treatment on NH₃-nitrided oxide is used to prepare thin gate oxide. Experiments on MOS capacitors and nMOSFET's with this kind of gate dielectric show that N₂O treatment is superior to conventional reoxidation step in suppressing both electron and hole trappings and interface trap creation under high-field stress. Interface hardness against hot-carrier bombardment and neutral electron trap generation are also improved. Thus, N₂O treatment on NH₃ -nitrided oxide shows excellent electrical and reliability properties, while maintaining sufficiently high nitrogen concentration in gate oxide which offers good resistance to dopant penetration     

Optimization of gate oxide N2O anneal for CMOSFET's atroom and cryogenic temperatures

This paper presents a study of the impact of gate-oxide N₂ O anneal on CMOSFET's characteristics, device reliability and inverter speed at 300 K and 85 K. Two oxide thicknesses (60 and 110 Å) and five N₂O anneal conditions (900~950°C, 5~40 min) plus nonnitrided process and channel lengths from 0.2 to 2 μm were studied to establish the correlation between the nitrogen concentration at Si/SiO₂ interface and the relative merits of the resultant devices. We concluded that one simple post-oxidation N₂O anneal step can increase CMOSFET's lifetime by 4~10 times, effectively suppress boron penetration from the P⁺ poly-Si gate of P-MOSFET's without sacrificing CMOS inverter speed. We also found that the benefits in terms of the improved interface hardness and charge trapping characteristic still exist at cryogenic temperature. All these improvements are found to be closely correlated to the nitrogen concentration incorporated at the Si/SiO₂ interface. The optimal N₂O anneal occurs somewhere at around 2% of nitrogen incorporation at Si/SiO₂ interface which can be realized by annealing 60~110 Å oxides at 950°C for 5 min or 900°C for 20 min     

Uniform durable thin dielectrics prepared by rapid thermalprocessing in an N2O ambient

Thin dielectrics grown on silicon wafers by rapid thermal processing in an N₂O ambient at temperatures of 1100°C, 1150°C, and 1200°C are discussed. The resulting films, in conjunction with an O₂ ambient control were characterized by thickness measurements and electrical performance. Dielectrics formed in N₂O in this temperature range were all superior to that prepared in an O₂ ambient in terms of interface state generation and flatband voltage shift after constant current stressing. Although all N₂O prepared samples exhibited similar cross wafer electrical uniformity, higher growth temperatures favored thickness uniformity. The electrical behavior of the N₂O wafers was not strongly dependent on growth temperature; however, a 60-s 1100°C post-oxynitridation N₂ anneal was found to significantly reduce subsequent electrical performance. It is also demonstrated that under optimum process conditions, high-quality uniform dielectrics can be formed by RTP in N₂O     

High-field breakdown in thin oxides grown in N2O ambient

A detailed study of time-dependent dielectric breakdown (TDDB) in N₂O-grown thin (47-120 Å) silicon oxides is reported. A significant degradation in breakdown properties was observed with increasing oxide growth temperatures. A physical model based on undulations at the Si/SiO₂ interface is proposed to account for the degradation. Accelerated breakdown for higher operating temperatures and higher oxide fields as well as thickness dependence of TDDB are studied under both polarities of injection. Breakdown under unipolar and bipolar stress in N₂O oxides is compared with DC breakdown. An asymmetric improvement in time-to-breakdown under positive versus negative gate unipolar stress is observed and attributed to charge detrapping behavior in N₂O oxides. A large reduction in time-to-breakdown is observed under bipolar stress when the thickness is scaled below 60 Å. A physical model is suggested to explain this behavior. Overall, N₂O oxides show improved breakdown properties compared with pure SiO₂     

Improved flash cell performance by N2O annealing ofinterpoly oxide

In this letter, we report the effects of N₂O annealing of interpoly oxide on flash cell performance. It is demonstrated that by adding an N₂O anneal after interpoly oxide formation, improved cycling endurance is achieved. The program and erase efficiencies are also improved significantly, compared to the control cell without N₂O anneal. The cells with N₂O anneal show higher cell current (i.e., drain current), which can be ascribed to a lower threshold voltage and higher transconductance, compared to the control cell