Screening Effects in High Resistivity CdTe for X-ray and Gamma Ray Detectors

The possibility to estimate an upper limit of concentrations of defects forming deep levels in high-resistivity CdTe is discussed based on evaluation of room-temperature photocurrent spectra. A model explaining the shift of the maximum of photocurrent with the applied electric field as a consequence of screening effects caused by space charge accumulated on deep levels is presented. Theoretical calculations show that a maximum concentration of deep levels leading to the observed shift of the photocurrent maximum is less than ∼10¹³ cm⁻³ for typical capture cross sections of electrons and holes. This result supports the models assuming formation of a high-resistivity state with a minimum deep level doping.     

砷化镓衬底与MESFET中深能级研究

用波长范围为 70 0 nm到 350 0 nm的光电流测试系统研究了 SI- Ga As衬底、有源层和MESFET中的深能级。结果显示在 SI- Ga As衬底、有源层和 MESFET中的深能级有着较为密切的联系 ,这些深能级影响着器件的性能     

Electroluminescence properties of PbTe pn junctions fabricated under controlled Te vapor pressures

Electroluminescence properties of PbTe pn junctions grown under various tellurium vapor pressures are investigated. For unintentionally doped pn junctions, the luminescence bands corresponding to D-A pair and band to band transition are observed. The luminescence intensity of the band to band transition has depended on tellurium vapor pressure, which suggests nonradiative transitions through nonstoichiometric defects forming deep levels. For pn junctions with Bi-doped epitaxial layers, only one peak appears at 20∼25 meV below band to band-transition energy, which, probably, shows recombination through impurity levels or impurity band originating from Bi-doping.     

Effect of deep impurity levels on Schottky barrier diode characteristics

In the presence of an arbitrary number of deep donor levels volt-ampere and volt-farad characteristics are obtained for the Schottky barrier diode which contains a thin dielectric layer between the metal and the semiconductor. The analysis of these characteristics shows that the deep levels can significantly influence both the capacitance and the rectifying properties of the Schottky diode; the thicker the dielectric layer, the greater the effect of the deep levels upon volt-ampere relationship and the lesser upon volt-farad one. One can determine the parameters of the deep levels from these relationships. The results of the calculation are in agreement with the data of the experiment performed.     

一种基于面阵的旁瓣对消方法

目前基于阵列的旁瓣对消方法,主要是通过自适应算法对各阵元进行幅度和相位加权,使得阵列波束图在于扰方向上形成零陷,即可对该方向上的干扰进行抑制。由于利用了自适应算法,所以随着阵元数的增多,该算法的硬件实现将越来越难,甚至会导致算法失效。以面阵为倒,提出了两种在干扰来波方向上快速形成零陷的方法。这两种方法摒弃了以往方法中的自适应权值求取过程,只需要利用事先求取好的权值对选定的阵元进行加权处理,极大地增强了系统的实时处理能力。另外,两种方法形成的零陷足够深且宽,对主瓣没有影响。     

半绝缘砷化镓及其MESFET器件光敏特性研究

用波长范围为 70 0～ 3 5 0 0 nm的光电流测试系统研究了 SI-Ga As衬底及其 MESFET器件中的深能级。结果显示在 SI-Ga As衬底及其 MESFET器件中存在着相似的深能级 ,衬底的深能级影响着器件的光敏等性能。还讨论了如何减少器件中光敏现象的方法。     

SLM成型件表面球化程度表征方法及等级检测

球化现象是选区激光熔化(SLM)成型过程中最常发生的缺陷,同时影响了最终成型部件的疲劳寿命和物理性能。合理控制部件成型过程中球化现象的发生,对维持成型过程的持续进行以及获得高质量的成型部件具有重大意义。本文在研究SLM成型过程中部件表面球化特征提取方法的基础上提出了球化程度表征方法,并通过正交实验验证了球化程度表征方法的有效性,建立了球化程度与激光能量密度之间的关联关系。同时对球化程度等级做了界定,最终构建了深度卷积神经网络(CNN)模型自动识别部件表面球化程度等级,以辅助实验及生产人员做出相应的决策。模型识别结果表明,在小的图像分割集上,网络识别精度达到了964,当在所采集的全局显微图像集上,其识别精度达到了100,取得了良好的识别效果。本研究将为SLM成型过程中成型质量的实时控制提供有效实现途径。     

波束形成和解码的联合迭代接收技术

SDMA技术是提高频谱利用率的有效技术，但在判决反馈最小均方波束形成中，在深衰落之后期望用户波束会指向干扰用户,严重影响了波束形成的性能。文中提出在波束形成和信道解码之后，经过编码、交织，重新生成波束形成的参考信号，再进行波束形成，有效克服了深衰落之后的波束指向错误。计算机仿真结果证明了该方法的有效性。     

Research and development of deep anisotropic plasma silicon etching process to form MEMS structures

Process characteristics of deep silicon etching as a function of its operational parameters are investigated. A process of deep anisotropic plasma etching process is developed and optimized to form MEMS silicon structures. The results of the work are used in forming MEMS working structures.     

消除边缘区效应的“三脉冲DLTS”法及对DX-中心俘获过程的测量

本文提出了一种新的方法──“三脉冲DLTS”法,用于测量深能级的热俘获截面,目的在于消除使测量产生很大误差的边缘区效应的影响,最后用这种方法,对AlGaAs:Si中DX—中心的电子热俘获截面进行了测量,结合考虑大的深能级浓度这一因素,通过计算机的拟合过程,给出了非常令人满意的结果。     

Uniformity of deep levels in semi-insulating InP obtained by multiple-step wafer annealing

The uniformity of deep levels in semi-insulating InP wafers, which have been obtained by multiple-step wafer annealing under phosphorus vapor pressure, was studied using the thermally stimulated current (TSC) and photoluminescence (PL) methods. Only three traps related to Fe, T₀ (ionization energy E_i=0.19 eV), T₁ (0.25 eV), and T₂ (0.33 eV), probably forming complex defects, were observed in the wafer and they exhibited a relatively uniform distribution. PL spectra relating to phosphorus vacancies observed in some regions of the wafer are correlated with a small TSC signal having an ionization energy of 0.43 eV.     

Deep levels and nonlinear characterization of AlGaN/GaN HEMTs on silicon carbide substrate

Deep levels in AlGaN/GaN high electron mobility transistors (HEMTs) on SiC substrate are known to be responsible for trapping processes like: threshold voltage shift, leakage current, degradation current, kink effect and hysteresis effect. The related deep levels are directly characterized by conductance deep level transient spectroscopy (CDLTS) method. Hereby, we have detected five carrier traps with activation energy ranging from 0.84 to 0.07 eV. In this study, we have revealed the presence of two hole-like traps (HL1 and HL2) observed for the first time by CDLTS with activations energy of 0.40 and 0.84 eV. The localisation and the identification of these traps are presented. Finally, the correlation between the anomalies observed on output and defects is discussed.     

Electronic properties of low-temperature InP

We have investigated InP layers grown by low-temperature (LT) gas source molecular beam epitaxy. Using high-pressure hall effect measurements, we have found that the electronic transport in the LT epilayers is determined by the presence of the dominant deep donor level which is resonant with the conduction band (CB) located 120 meV above the CB minimum (E_CB). We find that its pressure derivative is 105 meV/GPa. This large pressure derivative reveals the highly localized character of the donor which via auto-ionization gives rise to the high free electron concentration n. From the deep level transient spectroscopy and Hall effect measurements, we find two other deep levels in the band gap at E_CB−0.23 eV and E_CB−0.53 eV. We assign the two levels at E_CB 0.12 eV and E_CB−0.23 eV to the first and second ionization stages of the phosphorus antisite defect.     

Ultrasound-Controlled Electron-Phonon Coupling Augmenting Catalysis of Piezoelectric-Based Sonosensitizer Safely Against Osteomyelitis

The energy transfer way and efficiency of ultrasound (US) to piezoelectric materials in fluid determines the US catalytic performance of materials and the subsequent sono-therapeutic effects for deep infection diseases. Herein, on insonation, the microbubble cavitation occurs near the surface of barium orthotitanate/berberine chloride nanoparticles (BTO/Ber NPs), often forming sonoluminescence and high pressure. The light further activates Ber, and the electron transfer happens between activated Ber and changing energy levels of BTO NPs caused by changing pressure. Meanwhile, ultrasound-driven piezoelectric electron-phonon coupling simultaneously narrows bandgap and prolongates carrier-lifetime, leading to more ROS generation. Hence, BTO/Ber NPs show great antibacterial activity against Staphylococcus aureus (99.80 ± 0.09%) by microbubble-mediated sonoporation and catalysis. Meanwhile, BTO/Ber NPs improve bone regeneration by decreasing the inflammatory response and enhancing osteoblast differentiation. US-mediated microbubbles may offer a safe and efficient treatment to millions of patients suffering from osteomyelitis and pave the way for the highly safe use of ultrasound in deep infections.     

A study of deep centers in microplasma channels in GaP light-emitting diodes with green-emission spectrum

The statistical delay of microplasma breakdown in GaP light-emitting diodes with the green-emission spectrum is studied. The unusual profound effect of deep centers on the statistical delay of avalanche breakdown is observed in the temperature range of 300–380 K; this effect is caused by a variation in the charge state of these centers due to a reduction in the reverse bias applied to the p–n junction. Four deep levels are revealed and their parameters are determined.     

Inverse current gain improvement of bipolar transistors by double-base diffusion

The double-base diffusion process is introduced and is experimentally shown to significantly improve the inverse or upward current gain of the n-p-n bipolar transistor. The technique consists of a deep p⁺diffusion into an external base region of multicollector transistors forming a close-in collar around the intrinsic base of each transistor. This technique, together with the use of deep diffusion n⁺guard rings around the complete unit cell, is shown to improve the inverse current gain significantly.     

Deep levels in Si-implanted and rapid thermal annealed semi-insulating gaAs

Deep levels have been investigated in Si-implanted and rapid-thermal-annealed semiinsulating GaAs:Cr, which was grown by a horizontal Bridgman method. Samples were implanted with a Si-dose of (1 - 5) x 10¹² ions cm^-2 with 100 keV energy, and treated by a two-step rapid thermal annealing process at 900 and 800° C. After these processes, three electron deep levels at 0.81, 0.53 and 0.62 eV below the conduction band and three hole deep levels at 0.89, 0.64 and 0.42 eV above the valence band were observed. The new deep levels E_c - 0.53 eV, E_c - 0.62 eV, andEv + 0.64 eV in fact, dominate the implantation and/or the thermally damaged region, but are not found in the bulk. These results indicate that high-density deep levels may be induced near or within the implanted region by rapid heating and cooling, and that these defects may effect carrier activation.     

Influence of electric-field-assisted thermal ionization on the formation of the schottky barrier between metal and amorphous silicon

The expression for a distribution function of charge carriers over deep levels in terms of the Poole-Frenkel effect in the space charge region is obtained. The inclusion of this effect permitted us to calculate the influence of the electric-field-assisted thermal ionization effect on a space charge density, a distribution of potential in the space charge region, and quasistatic capacitance-voltage characteristics of the metal-〈amorphous silicon〉 contact.     

Damage removal/dopant diffusion tradeoffs in ultra-shallowimplanted p+-n junctions

The tradeoffs between implant damage annealing and shallow junction formation are investigated. For very-low-energy amorphizing implants the time for damage anneal has a fourth-power dependence on depth below the Si surface. The depth effect depends on the type of amorphizing ion. It is shown that as a result, implanted B in Ge-preamorphized Si diffuses with no detectable self-interstitial supersaturation if the damage is <600 Å deep. Conditions for forming defect-free, shallow p⁺-n junctions are described in design curves and comparisons are made between several junction-formation approaches. Implantation of B at energies below 2 keV offers an attractive way of achieving 500-Å junctions     

中国深空测控网光通信技术途径分析与发展展望（特约）

深空光通信是满足未来深空探测高速数据传输的主要技术途径,也是未来中国深空测控网发展的主要技术方向。特别是伴随着智能化、网络化空间通信系统的发展,射频和光通信相结合的智能空间通信网络将成为支持未来深空探测任务的核心设施。文中结合中国未来月球和深空探测发展规划,以中国现有深空测控网的任务支持能力为基础,梳理了未来深空测控光通信的需求。在充分借鉴国内外最新研究成果的基础上,全面分析了建设深空光通信系统地球终端的技术途径。结合中国国情的实际,提出了分步进行系统建设、分阶段开展工程应用,构建天地基相结合的混合深空光通信地面系统,并最终形成中国完全自主的深空光通信认知网络的发展思路。