超快大功率SiC光导开关的研究

选用钒掺杂浓度为0.2at％的高质量6H-SiC晶体, 电阻率为7.0×10⁸Ω·cm, 研制出超快大功率SiC光导开关. 在脉冲宽度为20ns的光源激发下, 分别测试了在不同的偏置电压和光能条件下开关的电脉冲输出特性. 结果表明: 1mm电极间隙的SiC开关器件的性能优越, 耐偏压高, 光导电脉冲的上升时间快(6.8ns), 脉宽<20ns, 稳定性好. 负载为40Ω的电阻上输出线性电脉冲电压随开关的偏置电压和光强增大而增大, 在2.5kV的偏置电压, 最大瞬时电流约为57.5A, 瞬时功率高达132kW.     

基于光导开关脉冲偏置电压的太赫兹时域光谱系统

利用光导开关产生脉冲偏置电压的方式改进了基于光电导天线的太赫兹时域光谱系统.在分析光电导天线产生THz波原理的基础上,重点研究了目前基于光电导天线的太赫兹时域光谱系统存在的问题,探讨了解决斩波器引起的机械噪声和光电导天线脉冲偏置电压之间矛盾的途径.最后,通过对光导开关的特性测试,提出了利用高压直流电源、光导开关和纳秒激...     

p型Na掺杂ZnMgO薄膜的光电导性能

采用脉冲激光沉积(PLD)方法在石英衬底上制备p型Na掺杂ZnMgO薄膜,薄膜在氮气气氛中600℃退火60s,具有较好的光电性能。在室温下分别用波长254nm的紫外光和波长630nm的红色激光对样品进行了光电导性能测试。两种光照下,光电流均瞬间上升,且光响应度与外加偏压具有线性相关性。紫外光照下p型Na掺杂ZnMgO薄膜的光电流变化比红色激光照射下要显著。     

Si基GaN紫外光探测器

报道了以Si(111)为衬底的GaN光导型紫钙探测器的制备及其光电流性质,探测器的光谱响应表明,这种GaN探测器在紫外波段250－360nm有近于平坦的光电流响应,36nm附近陡峭的截止边,在357nm波长处,测得5V偏压下的响应度高达6．9A／W。响应度随外加偏压的增加而增加,5V时达到饱和,通过拟合光电流响应随入射光调制频率的变化关系,得到GaN探测器的响应时间为4．8ms。     

C面蓝宝石衬底上6H-SiC薄膜的低压化学气相外延生长与表征

采用低压化学气相沉积方法在C面蓝宝石衬底上异质外延生长出高结晶质量和良好表面形貌的6H-SiC薄膜,研究了CsHs气体流速对薄膜结晶质量的影响.随着C3Hs气体流速的降低,薄膜的结晶质量先增加后降低,表明薄膜的生长在开始阶段受表面反应控制,而后受质量输运控制.所得到的结晶质量最好的6H-SiC薄膜,其摇摆曲线半高宽为0.6°,已经达到单晶水平.没有使用A1N过渡层,制备出结晶质量更好的SiC薄膜,表明对于蓝宝石衬底上SiC薄膜的生长,起决定性因素的是温度,过渡层不是影响SiC薄膜结晶质量的主要因素.     

尘埃粒子计数信号幅度的对数正态分布

对尘埃粒子计数器计数信号幅度统计分布进行了研究,试验表明粒子光散射脉冲信号幅度分布并不具有严格的对称性.在光电传感器检测阈值附近,单径粒子脉冲信号幅度分布半宽度与信号幅度平均值相近时,与均匀划分电压通道对应的信号幅度服从对数正态分布.计算结果证明,在相对于平均值的离散度σ1的条件下,对数正态分布将趋近于正态分布.     

6H-SiC单晶表面ZnO薄膜的制备及其结构表征

利用脉冲激光淀积(PLD)技术在6H-SiC单晶衬底上制备了ZnO薄膜. 利用X射线衍射(XRD), 反射式高能电子衍射(RHEED)和同步辐射掠入射X射线衍射(SRGID)φ扫描等实验技术研究了ZnO薄膜的结构. 结果表明:在单晶6H-SiC衬底上制备的ZnO薄膜已经达到单晶水平, 不同入射角的SRGID结果, 显示了ZnO薄膜内部不同深度处a方向的晶格弛豫是不一致的, 从接近衬底界面处到薄膜的中间部分再到薄膜的表面处, a方向的晶格常数分别为0.3264、0.3272和0.3223nm. 通过计算得到ZnO薄膜的泊松比为0.504, ZnO薄膜与单晶6H-SiC衬底在平行于衬底表面a轴方向的实际晶格失配度为5.84%.     

PLD法生长高质量 ZnO薄膜及其光电导特性研究

采用脉冲激光沉积（PLD）法在单晶Si（100）衬底上生长ZnO薄膜，以X射线衍射（XRD）和场发射扫描电镜（SEM）等手段分析了所得ZnO薄膜的晶体结构和微观形貌．结果表明，随着衬底温度和薄膜生长时氧分压的增加，ZnO薄膜的晶体结构和化学计量比得到显著改善．优化工艺（700℃，20Pa）下生长的ZnO薄膜呈c轴高度择优取向，柱状晶垂直衬底表面生长，结构致密均匀．以不同暗电阻的ZnO薄膜为材料，利用剥离（1ift-off）技术制备了MSM结构ZnO光电导型紫外探测器．紫外光照射前后的I-V特性测试表明ZnO薄膜产生非常明显的光电导现象，分析了其光电响应机理．     

ITO/PZT-Ag2O/Pt铁电薄膜的光伏特性

研究了在透明导电ITO玻璃衬底上制备PZT-Ag2O铁电薄膜的工艺条件,并测量和表征了在不同衬底温度下生长的薄膜的相结构、表面形貌、铁电性能和光电特性。结果表明:在ITO玻璃衬底上可制备出铁电性能较好的PZT-Ag2O铁电薄膜;ITO/PZT-Ag2O/Pt铁电器件实现了可见光响应,其短路光电流和开路电压随极化电压的变化呈回线关系;产生这一现象的物理机制为:光生短路电流和开路电压的大小取决于退极化场和界面肖特基势垒的综合作用,不同的外加极化电压在PZT薄膜诱导出强度不同的退极化场,从而使光生短路电流和开路电压与外加极化电压呈回线型关系。     

用于超短激光脉冲检测的新型光电薄膜的量子产额

超短激光脉冲的研究已经成为基础科学与应用科学研究的重要内容，对用于检测这种信号的光电发射功能薄膜的研究也受到人们极大重视。Ａｇ－Ｂａ－Ｏ薄膜是一种可以经历暴露大气，用于超短激光脉冲检测的新型光电发射材料，光电薄膜在超短激光脉冲作用下的量子产测量与普通可见光作用下量子产额的测量有很大不同。光激光波长为１．０６μｍ，激光的功率密度为１０＾７－１０＾８Ｗ／ｃｍ＾２，选单光脉冲宽度为４０ｐｓ时，经历暴露大     

Raman spectroscopic investigation of solid samples using a low-repetition-rate pulsed Nd:YAG laser as the excitation source

We tried to investigate the possibility of using a low-repetition-rate pulsed Nd:YAG laser as an excitation source in Raman measurements for solid samples. Based on the results from the Raman spectra excited by continuous wave (CW) 532 and 325 nm lasers, we studied the influence of laser energy and irradiation time of 532 and 355 nm pulsed Nd:YAG lasers (10 Hz repetition rate) on the thermal stability of (NH4)6Mo7O(24).4H2O, NH4VO3, and Ce(NO3)(3).6H2O samples, which usually decompose at relatively low temperatures. It is observed that the heating temperature estimated at these samples caused by the irradiation of 532 nm pulsed laser with 22 mJ is no higher than 100 degrees C even for 60 min exposure. The 355 nm pulsed laser with energies below 8.0 mJ hardly causes thermal damage to hydrated (NH4)6Mo7O24 and hydrated Ce(NO3)3 SAMPLES: However, a 355 nm pulsed laser with only 2.2 mJ causes heating temperatures as high as 200 degrees C in the NH4VO3 SAMPLE: These great differences should be attributed to the electronic absorbance of the above three samples at 355 nm. We also found that a 532 nm pulsed laser with even 22 mJ and a 355 nm pulsed laser with even 8.0 mJ do not cause the phase transition of TiO2 and ZrO2, whose phase transformation easily takes place at elevated temperatures, but pulsed lasers could remove some oxygen atoms from these samples. In addition, for L-alanine and DL-beta-phenylalanine biological samples, it is surprisingly found that they are not damaged by the 355 nm pulsed laser even when the laser energy is increased to 8.0 mJ, possibly because they do not absorb the 355 nm laser. Based on these results, it is demonstrated that low-repetition-rate pulsed lasers with appropriate wavelength and energy can be employed as the excitation sources of Raman spectroscopy for characterizing some solid samples, even the thermally unstable samples.     

Effect of electron acceptor type on nonlinear optical absorption properties in the chiral polymers based on polybinaphthyls

Nonlinear optical absorption properties of two chiral polybinaphthyls with the same backbone but different electron acceptor hydroxyl and octoxy were studied in tetrahydrofuran solution. When excited by 100 fs 800 nm laser pulses, the up-converted fluorescence were observed and the intensities related to the different input irradiances were measured to confirm the two-photon excited fluorescence. The two-photon absorption coefficients were obtained as 4.82 cm GW⁻¹ and 12.36 cm GW⁻¹ with 100 fs pulses at 800 nm for two polymers, respectively. Under the excitation of 532 nm 38 ps pulse, it was found that the polymer with the side-chain of hydroxyl showed saturable absorption while the polymer with the side-chain of octoxy presented reverse saturable absorption. Their different nonlinear absorption behavior resulted from the fact that the ground-state absorption cross-section in the latter polymer was about 10 times larger than that of the former polymer while the excited-state absorption cross-section represented similar.     

Study of the nonlinear optical properties and behavior in phenoxy-phthalocyanines liquid at nanosecond laser pulses

The nonlinear optical properties of 2,9,16,23-phenoxy-phthalocyanine (Pc1) and 2,9,16,23-phenoxy-phthalocyanine-zinc (Pc2) in solution were investigated under excitation with nanosecond laser pulses at 532 nm. Based on five-level model, the nonlinear absorption in nanosecond regime was theoretically analyzed. The A-OS and OL behavior of Pc1 and Pc2 were further investigated with the pump–probe technique and transmission measurement technique. The results show that the A-OS response time is determined by the lifetime of the first triplet excited state of molecule, and Pc1 and Pc2 exhibit strong optical limiting effect at nanosecond laser pulses. These studies make the samples a promising possibility for device realization.     

Encryption of nonlinear optical signals in ZnO:Al thin films by ultrashort laser pulses

Described herein is the effect of optical annealing on the third-order non-linear optical properties exhibited by nanostructured Al-doped ZnO thin films. The samples were synthetized by an ultrasonic spray pyrolysis method. The optical annealing process was carried out by laser pulses at 532, 835 and 1064 nm wavelengths with, ps, fs and ps pulse duration, respectively. The optical non-linearity of the films was measured by the z-scan method with three different irradiations of excitation: 100 fs at 835 nm, 120 ps at 532 nm, and 150 ps at 1064 nm. The as-grown samples showed a saturable optical absorption that evolves into two-photon absorption transitions by a picosecond optical annealing phenomenon induced at 532 nm wavelength. Potential applications for developing optical encryption functions were considered.     

Improvement in light extraction efficiency in group III nitride-based light-emitting diodes using moth-eye structure

Group III nitride-based blue light-emitting diodes with a moth-eye structure at the bottom of a semi-insulating transport 6H-SiC substrate were fabricated. Self-assembled Au nanomasks and CF₄ reactive ion etching were used for the fabrication of the moth-eye structure. We succeeded in forming cones with a mean period of approximately 160 nm and a mean height of approximately 400–600 nm. The period of 160 nm is shorter than the optical wavelength. The light extraction efficiency and the corresponding output power of the moth-eye-structured light-emitting diodes (LEDs) increased approximately three-fold those of LEDs with a conventional structure.     

Fabrication and parameters of a 1310-nm buried heterostructure operating in the microwave region

InGaAsP/InP nanoheterostructures have been grown by liquid phase epitaxy and their structural perfection has been studied. The nanoheterostructures have been used to fabricate buried mesa laser diodes on a p-InP substrate that emit in the spectral range 1310–1550 nm. The design of the buried mesa stripe diode with the use of a semi-insulating II–VI compound has made it possible to create laser diodes operating at a wavelength of 1310 nm with a telecommunication signal transfer rate of 5.5 GHz. The results are technologically attractive and reproducible. We analyze potentialities for further increasing the optical signal transfer rate.     

Energy dependent saturable and reverse saturable absorption in cube-like polyaniline/polymethyl methacrylate film

Solid films of cube-like polyaniline synthesized by inverse microemulsion polymerization method have been fabricated in a transparent PMMA host by an in situ free radical polymerization technique, and are characterized by spectroscopic and microscopic techniques. The nonlinear optical properties are studied by open aperture Z-scan technique employing 5 ns (532 nm) and 100 fs (800 nm) laser pulses. At the relatively lower laser pulse energy of 5 μJ, the film shows saturable absorption both in the nanosecond and femtosecond excitation domains. An interesting switchover from saturable absorption to reverse saturable absorption is observed at 532 nm when the energy of the nanosecond laser pulses is increased. The nonlinear absorption coefficient increases with increase in polyaniline concentration, with low optical limiting threshold, as required for a good optical limiter.