Czochralski-grown nitrogen-doped silicon: Electrical properties of MOS structures; A positron annihilation study

Czochralski-grown nitrogen-doped (NCZ) silicon was studied using different methods. Measurements of interface traps density, effective generation lifetime and effective surface generation velocity were performed on selected Metal-Oxide-Semiconductor (MOS) structures. Application of the positron annihilation technique (PAS)—pulsed low energy positron system (PLEPS)—was focused on the detection of nitrogen-related defects in NCZ silicon in the near surface region. PAS—PLEPS technique gave relevant results on p-type NCZ silicon. Low sensitivity in the application to n-type NCZ silicon discriminates the PAS—PLEPS technique and should be alternated by other experimental technique. On the other hand, more pertinent measurement of generation lifetime was performed on MOS structures with n-type Si. Although the generation lifetime decreases in NCZ silicon, considerable lateral homogenization of the relaxation time was observed on the wafer.     

锑化铟晶体空位缺陷的正电子湮灭研究

锑化铟晶体材料的电学性能是影响最终制备的红外探测器件性能的关键因素。材料内部的杂质以及点缺陷特别是空位缺陷会极大的影响材料的电学性能,有时甚至会导致材料反型。本文利用正电子湮灭谱对锑化铟晶体材料的空位缺陷类型进行了研究,同时还对不同晶体生长拉速、导电类型晶体材料的正电子湮灭寿命进行分析。结果表明其内部主要为VIn型空位缺陷,且在一定拉速范围内,正电子湮灭寿命基本无变化,此外空位缺陷也不是导致N型锑化铟晶体材料导电类型反型的主要原因。     

YBa2Cu3O6.92超导体光电导效应的正电子实验研究

报道了对光辐照ＹＢａ２Ｃｕ３Ｏ６．９２材料的正电子寿命谱研究结果，给出了正电子寿命参数随辐照时间变化的基本特征，利用两态捕获模型对实验结果进行了初步分析，计算了局域电子密度ｎｅ和空位浓度Ｃｖ随辐照时间的变化，发现光诱导而产生Ｃｕ－Ｏ链区域电子结构的变化，证明Ｏ（１）和Ｏ（５）位之间的氧迁移和重新分布使得氧有序乃是光诱导电性的主要原因，为ＹＢａ２Ｃｕ３Ｏ６．９３体系光电导机理的理解提供了重要的正电子     

用PAT研究SrTiO3双功能陶瓷的缺陷结构

测定了不同气氛烧结的SrTiO₃双功能陶瓷的正电子湮灭(PAT)寿命谱,其平均寿命随着烧结气氛中H₂含量的增加而减小.这是还原烧结气氛使瓷体中形成较多的氧缺位,氧缺位捕获两个弱束缚电子形成F'-色心所致.弱束缚电子在禁带内形成局域能级,并使材料的电子浓度增大.x衍射分析结果证明了材料晶体结构的变化.     

Defects in Zn1−x−yCoxMgyO nanoparticles: Probed by XRD,RAMAN and PAS techniques

Wurtzite Zn_1?x?yMg_xCo_yO nanoparticles of size 14–20 nm are synthesized by the conventional coprecipitation route and are analyzed using XRD, FESEM, UV–visible, Raman, and Positron annihilation spectroscopic techniques. XRD patterns reveal formation of a single wurtzite phase of ZnO on adding Mg, Co or both. In addition to six Raman active modes corresponding to the wurtzite structure of space group C_6ν⁴, we also observe additional Raman modes at 519, 544 and 673 cm^?1 irrespective of the dopant type and concentration. These modes exactly match with the silent vibrational modes of ZnO lattice as calculated by the ab initio calculations. From positron life time measurements, we observe that while the shortest lifetime τ₁, the lifetime of positrons that annihilate in the grain boundary regions match well with the lifetime of positrons in a defect free ZnO (τ₁～158 ps), the intermediate lifetime, τ₂ of all three samples match with the life time of positron annihilating at the cluster of (Zn+O) di-vacancies. We conclude that the origin of additional Raman modes is not due to impurities as reported in the literature rather is due to host lattice defects.     

Silver gallium telluride (AgGaTe2) single crystal: Synthesis,accelerated crucible rotation-Bridgman growth and characterization

A silver gallium telluride single crystal of diameter 12 mm and length 80 mm was successfully grown by the vertical Bridgman method using accelerated crucible rotation technique. To confirm the unit cell parameters of the grown silver gallium telluride (AgGaTe₂) crystal, single crystal X-ray diffraction studies were carried out. AgGaTe₂ has been studied using differential scanning calorimetry and is found to have supercooling of 13 °C. AgGaTe₂ shows Fourier transform infrared transmission in the spectral range of 6000–500 cm⁻¹. The composition of Ag, Ga and Te in the grown crystal was measured with energy dispersive X-ray analysis spectroscopy. The optical band gap for AgGaTe₂ is 1.8 eV. In the positron lifetime measurements, the average lifetime 267 ps corresponds to vacancy clusters in AgGaTe₂ crystal. Hall measurements confirm p-type nature of AgGaTe₂.     

用正电子湮没技术研究NTD InP中的诱生缺陷

采用正电子湮没技术对中子嬗变掺杂（ Ｎ Ｔ Ｄ） 后的磷化铟（ Ｉｎ Ｐ） 材 料进行了分析。 Ｎ Ｔ Ｄ Ｉｎ Ｐ 样品经退火后的低温实验结果表明,其正电子平均寿命均随温度升高而缩短。对掺 Ｓｎ的 Ｉｎ Ｐ 样品进行的低温实验也反映出同样的变化规律。文章分析了这一现象,并研究了嬗变后 Ｉｎ Ｐ 样品的退火特性     

On the application of methods of positron annihilation spectroscopy for studying radiation-stimulated processes in chalcogenide glassy semiconductors

Unirradiated and γ-irradiated (average energy E = 1.25 MeV and dose Φ = 2.41 MGy) chalcogenide glassy semiconductors (CGSs) As₂S₃ and Ge_15.8As₂₁S_63.2 are studied by positron annihilation lifetime spectroscopy (PALS) and Doppler broadening of the 0.511-MeV annihilation line (DBAL). Two ²²Na positron sources with activities of 0.6 and 2.0 MBq and Kapton film thicknesses of 8.0 and 25.0 μm, respectively, are used. It is shown that radiation-induced changes in the PALS parameters of the CGS types under study are within measurement errors. The DBAL method appeared more efficient and accurate for studying radiation-stimulated processes in CGSs.     

Exchange interaction of electron and positron bunches

Exchange interaction of electron and positron bunches is simulated using the particle-in-cell method and macroscopic electron and positron wave functions. It is shown that a periodic exchange process with low or high nonlinearity is realized during variations in the electron and positron concentrations.     

Correlation between forward voltage drop and local carrier lifetimefor a large area segmented thyristor

The forward voltage drop for individual segments of a large area thyristor has been correlated to the local, bulk carrier lifetime by lifetime mapping of the the wafer after final device processing. The lifetime mapping was performed under high injection conditions using an all-optical technique where carriers were generated by a short YAG laser pulse and the subsequent carrier decay was monitored by an IR laser beam using free carrier absorption. The lateral resolution was ~100 μm. The lifetime map revealed heavily contaminated areas where the lifetime was reduced by more than an order of magnitude. The forward voltage drop for corresponding thyristor segments was high and, for some areas, no stable turn-on could be achieved. Deep Level Transient Spectroscopy characterization of contaminated areas confirmed the lifetime measurement results and suggest that the contamination is most likely due to metal impurities introduced in the first extended-time/high-temperature drive-in of the p-base. Device simulations showed qualitative agreement between the bulk carrier lifetime and the corresponding voltage drop     

Structure study of a metallic glass using positron annihilation methods

The effects of vitrification and cold rolling on the structure in a metallic glass of Pd_.775Cu_.06Si_.165 alloy and crystalline Pd have been investigated using positron lifetime and angular correlation measurements. It is concluded that: A) the metallic glass contains a negligible concentration of vacancy-like defects and the crystallite model may be excluded as a possible structure of metallic glasses, B) the glass-crystalline boundaries contain a very small fraction of vacancy-like defects and exhibit a smooth transition structure from glassy to crystalline regions, C) the cold rolling of the metallic glass induces no vacancy or dislocation-like defects and plastic flow in metallic glasses is accompanied by cooperative atomic regroupings somewhat analogous to the visco flow of glasses near the glass transition temperature, D) the electronic structure of the Pd-Cu-Si alloy alters little upon disordering from a crystalline to glassy state, but exhibits a large change from that of crystalline Pd. This is attributed to the valence electrons transferred from Si to the d-shell of Pd in the Pd-Cu-Si alloy.     

Nafion–Carbon Nanocomposite Membranes Prepared Using Hydrothermal Carbonization for Proton‐Exchange‐Membrane Fuel Cells

Nafion–carbon (NC) composite membranes were prepared by hydrothermal treatment of Nafion membrane impregnated with glucose solution. The carbon loading of the NC membrane was tuned by controlling the hydrothermal carbonization time. X‐ray diffraction, Fourier‐transform infrared spectroscopy, scanning electron microscopy, thermogravimetric analysis, and positron annihilation lifetime spectroscopy were used to characterize plain Nafion and NC composite membranes. Nafion–carbon composite membranes exhibited better proton conductivity and reduced methanol permeability than those of the plain Nafion membrane. A single cell prepared with the NC composite membrane with a carbon loading of 3.6 wt% exhibited the highest cell performance. Compared with the cell performance of plain Nafion membrane, the maximum power density of the new cell improved by 31.7% for an H₂/O₂ fuel cell at room temperature, and by 44.0% for a direct methanol fuel cell at 60 °C.     

Annihilation density distribution calculations for medically important positron emitters

The effect of positron range on the image-plane resolution of tomographic images is evaluated through calculations based on a model which employs beta-decay energy spectra and an empirical range formula. Predicted range distribution functions are compared with published measurements for three medically important positron emitters: (11 )C, (68)Ga, and (82)Rb. The effect of tomographic slice thickness on point-source annihilation distribution functions is also demonstrated. Line-spread functions are calculated using the model, for the above isotopes as well as for (18)F, (15)O, and (13)N. Image-plane resolution predictions are made for high-resolution positron cameras for various positron emitting isotopes with end-point energies up to 4 MeV.     

Reliability evaluation and prediction for silicon photodetectors

The electrical parameters of silicon detectors were measured under various external influences (temperature cycling, humidity, salt atmosphere, etc.). The tests were designed and the data were analyzed by using the randomized block design method from the SAS software package. To estimate the lifetime of the detectors, an accelerated lifetime was implemented. Using plots of inspected interval data based on the maximum-likelihood technique (using the software package CENSOR), it was found that the Weibull distribution fits the lifetime test data. The cumulative distribution function and the acceleration factor were calculated; the median lifetime of the silicon detector at room temperature was 8.94×10⁶ hours, and the 95% s-confidence interval was (71.6-10.6)×10⁶ hours     

DC/DC电源模块可靠性评价方法研究

提出了一种DC/DC电源模块使用寿命可靠性评价方法。在高温环境下进行长期寿命试验,利用试验过程中出现的失效数及总的试验时间,通过一定置信度下的数学计算,得到加速寿命试验的失效时间。依据DC/DC电源模块激活能的工程值计算加速系数,得到该DC/DC电源模块的使用寿命。结果表明,该DC/DC电源模块的使用寿命数据与设计值(15~20年)较吻合。该计算方法具有相当好的合理性。     

Defects introduced into SrTiO3 by auto-feeding epitaxy studied using positron annihilation technique

Vacancy-type defects in SrTiO₃ were studied by means of positron annihilation. Thin CeO₂ films were grown on SrTiO₃ substrates by molecular-beam epitaxy without using an oxidant; oxygen was supplied by diffusion from the substrate. This process is referred as “auto-feeding epitaxy” (AFE). The species of defects introduced into the substrate was found to be not only oxygen vacancies but also Sr-vacancies or their complexes. CeO₂ films were grown also on MgO, yttria-stabilized zirconia and sapphire substrates using AFE, and these substrates were characterized by positron annihilation.     

使用太赫兹快速探测器测量硅少数载流子寿命

利用脉冲触发信号在半导体中产生非平衡态载流子的方式,提出一种使用太赫兹连续源和超快速响应探头测量半导体少数载流子寿命的方法,用于表征半导体的瞬态载流子动力学过程。根据上述设计原理及思路,以泵浦光作为周期性激励信号,搭建出一套工作时间窗口为纳秒到秒量级,时间精度在纳秒量级的非接触式半导体少数载流子寿命测量系统,具有装置简单、操作方便、成本低廉等优点。使用搭建的系统对不同掺杂类型、不同掺杂浓度、不同厚度单晶硅的非平衡态少数载流子寿命进行测量。最后,通过改变泵浦光单脉冲能量,对单晶硅光生载流子寿命进行测量,结果表明单晶硅少数载流子寿命随着泵光能量的增大而变长。该系统所实现的宽工作窗口、高时间精度太赫兹快速过程的探测,可应用于太赫兹领域的快速成像和快速生物响应探测。     

Carrier lifetime measurement of a junction laser using direct modulation

A carrier lifetime measurement under lasing conditions using microwave techniques is reported. The direct modulation characteristic of a junction laser is analyzed, based on the rate equations, and a resonance-like phenomenon of the modulated output is calculated at a fixed frequency determined by the parameters of the junction diode. This frequency occurs just before the modulation cutoff frequency of the diode. The minority carrier lifetime in the active region of the junction laser is expressed in terms of this frequency and other parameters. A modulation experiment was performed using a microwave frequency modulated bias pulse current. The resonance-like phenomenon was confirmed experimentally and the carrier lifetime was determined from the analysis presented here.     

Elemental specificity of ion cores and ionization entropy of vacancy-group-V-impurity atom pairs in Ge crystals: ACAR and DLTS data

The positron probing of the donor-vacancy (DV) complexes created in the single crystals of n-GeD (D=P, As, Sb, or Bi) by γ -irradiation Co-60 (T_irr.≈315 K) has been carried out by measuring the angular correlation of the annihilation radiation (ACAR). The maximum overlapping of the positron and electron wave functions in the subvalent shells of the ion cores has been determined for [1 1 1] crystallographic direction by normal approximation method. It has been found that this maximum is shifted from the nuclei of DV complexes in passing from the ion cores of atoms of a relatively small “size”, P and As, to more volumetric ion cores, Sb and Bi, respectively. The shift itself is accompanied by the increase of the probability of the high-momentum annihilation process of the trapped positron during its lifetime. This increase correlates well with the augmentation of the entropy of ionization revealed by DLTS (Markevich et al. Phys. Rev. B70 (2004) 235213) for group-V-impurity atom pairs in germanium. Kolmogorov-Chapmen formalism has been used for studying the probability of the high-momentum annihilation of positron trapped by DV complexes. The results obtained suggest that the growth of the configurational entropy in passing from the ion cores of relatively small “size” to more volumetric ones is accompanied by the relaxation of the ion cores inward towards the free volume related to the vacancy in DV complex.     

Bidimensional lifetime control for high-speed low-loss p-i-nrectifiers

In the paper a lifetime control technique able to control device carrier lifetime not only in the axial direction, but also in the longitudinal direction (two-dimensional (2-D) lifetime control), is analyzed. Static and dynamic losses of p-i-n diode using 2-D lifetime control are studied through mixed mode circuit-device simulations. It is shown that the 2-D technique gives a better tradeoff between static and dynamic behavior with respect to electron irradiation technique. The comparison with axial lifetime control shows that, notwithstanding similar performances achieved using the two techniques, 2-D lifetime control provides greater design flexibility