Muonium dynamics in transparent conducting oxides

The motional and electrical properties of positively charged muonium (Mu⁺)$({\mathrm{Mu}}^{+})$ centers in single crystal β-Ga₂O₃$\mathrm{\beta }\mathrm{-}{\mathrm{Ga}}_2{\mathrm{O}}_3$ are investigated via zero field muon spin relaxation (ZF-MuSR). Below room temperature we find two distinct shallow muonium centers with ionization energies of 7 and 16 meV. Above room temperature, at least three different Mu⁺ signals are resolved; two of these are metastable while the third shows characteristics of a stable ground state. As the temperature is elevated, metastable centers undergo several transitions. We obtain the relevant barrier energies associated with these site-change transitions. By 700 K, most muons occupy the mobile ground state, and an activation energy of about 1.65 eV is inferred for Mu⁺ diffusion from the hop rates obtained for this state.     

Time-resolved photoluminescence study of the red emission in nanoporous SiGe alloys

Porous Si_1−xGe_x (PSiGe) layers with efficient room temperature visible photoluminescence (PL) were elaborated by anodical etching from p-type doped epitaxial layers with Ge contents from 5 to 30%. The luminescence is characterised by a broad PL band centred at 1.8 eV. Time resolved photoluminescence decay is studied in porous silicon germanium as a function of germanium content, temperature, emission energies and surface passivation. The PL decay line shape is well described by a stretched exponential in all cases. The effective lifetime at low temperature in as prepared porous Si_1−xGe_x is 400 μs, i.e. an order of magnitude less than in porous silicon. After the formation of a 20 Å thick oxide surface layer we observe a decrease of the effective lifetime to 20 μs at T=4 K.     

Room-temperature SiGe light-emitting diodes

In the present paper the electroluminescence of PIN diodes with either strained SiGe/Si or Ge islands in the i-region has been investigated experimentally and by quantitative modelling. The modelling helped to improve the diode structure. Consequently, diodes with strained Si_0.80Ge_0.20 could be improved so as to reveal emission up to room temperature, if the thickness was high enough. To overcome the thickness limitation due to plastic relaxation, we used selective epitaxy on small areas. We also present results for diodes with Ge islands in the active region. The internal quantum efficiency of light emitting diodes with strained SiGe was at room temperature 10⁻⁴, while diodes with islands emitted ten times less light.     

Motion of positively charged muonium in ZnO

We report on a study of the motional characteristics of positively charged muonium defect centers in ZnO as an analog for H⁺ behavior. Muon spin depolarization measurements at zero applied magnetic field were completed from 20 K to 400 K, with preliminary results to 750 K. Results at the lower temperatures imply that Mu⁺ occupied two sites, and indicate local motion as thermally assisted tunneling with a characteristic energy of ∼60 meV, as well as a site change transition above 200 K with barrier energy ∼440 meV. Based on theoretical results, we have tentatively assigned these features to tunneling among three equivalent oxygen anti-bonding sites (AB_⊥) and a transition to a lower-energy bond-centered site (BC_‖) oriented along the c-axis. Preliminary fits suggest that global diffusion of muonium occurs above 400 K, with a diffusion barrier energy of ∼0.7 eV.     

SiGe HBT大信号等效电路模型

基于SiGe HBT(异质结双极晶体管)的物理模型，建立了描述SiGe HBT的大信号等效电路模型.该等效电路模型考虑了准饱和效应和自热效应等，模型分为本征和非本征两部分，物理意义清晰，拓扑结构相对简单.该模型嵌入了PSPICE软件的DEVEO(器件方程开发包)中.在PSPICE软件资源的支持下，利用该模型对SiGe HBT器件进行了交直流特性模拟分析，模拟结果与理论分析结果相一致，并且与文献报道的结果符合较好. 关键词： SiGe HBT 等效电路模型 PSPICE     

氧化SiGe/Si多量子阱制备Si基SiGe弛豫衬底

SiGe弛豫衬底是制备高性能Si基SiGe光电子器件的基础平台。本文通过1050℃不同时间氧化SiGe/SiMQW材料,分析氧化过程中Ge组分、弛豫度的变化趋势,制备位错密度低、表面平整、弛豫度超过60%的Si基Si0.75Ge0.25缓冲层。     

Oxidation process of SiGe on SOI substrates

The oxidation of SiGe film epitaxial grown on top of SOI wafers has been studied. These SiGe/SOI samples were oxidized at 700, 900, 1100 °C. Germanium atoms were rejected from SiGe film to SOI layer. A new Si_1−xGe_x (x is minimal) layer formed at SiGe/Si interface. As the germanium atoms diffused, the new Si_1−xGe_x (x is minimal) layer moved to Si/SiO₂ interface. Propagation of threading dislocation in SiGe film to SOI substrate was hindered by the new SiGe/Si interface. Strain in SOI substrate transferred from SiGe film was released through dislocation nucleation and propagation inner. The relaxation of SiGe film could be described as: strain relaxed through strain equalization and transfer process between SiGe film and SOI substrates. Raman spectroscopy was used to characterize the strain of SiGe film. Microstructure of SiGe/SOI was observed by transmission electron microscope (TEM).     

Physico-chemical and electrical properties of rapid thermal oxides on Ge-rich SiGe heterolayers

Rapid thermal oxidation of high-Ge content (Ge-rich) Si_1−xGe_x (x = 0.85) layers in dry O₂ ambient has been investigated. High-resolution X-ray diffraction (HRXRD) and strain-sensitive two-dimensional reciprocal space mapping X-ray diffractometry (2D-RSM) are employed to investigate strain relaxation and composition of as-grown SiGe alloy layers. Characterizations of ultra thin oxides (∼6-8 nm) have been performed using Fourier transform infrared spectroscopy (FTIR) and high-resolution X-ray photoelectron spectroscopy (HRXPS). Formation of mixed oxide i.e., (SiO₂ + GeO₂) and pile-up of Ge at the oxide/Si_1−xGe_x interface have been observed. Enhancement in Ge segregation and reduction of oxide thickness with increasing oxidation temperature are reported. Interface properties and leakage current behavior of the rapid thermal oxides have been studied by capacitance-voltage (C-V) and current-voltage (J-V) techniques using metal-oxide-semiconductor capacitor (MOSCAP) structures and the results are reported.     

锗硅合金半导体中无声子参与光跃迁机制研究

研究了Ｓｉ１－ｘＧｅｘ合金半导体中无声子参与光嗅迁的产机制，对由杂质无规分布引起的无声子参与光跃迁给出了一个物理模型。用此模型计算了光跃迁偶极矩，给出了跃迁偶极矩的上限。提出了未掺杂Ｓｉ１－ｘＧｅｘ合金半导体中无声子参与光跃迁的一种跃迁机制，认为是Ｇｅ原子周围波函数畸变的集体行为。     

SiGe HBT势垒电容模型

在考虑SiGe HBT的势垒电容时，通常的耗尽层近似不再适用，应考虑可动载流子的影响.在分析研究SiGe HBT载流子输运的基础上，建立了考虑发射结势垒区内载流子分布的发射结势垒电容模型和不同电流密度下包括基区扩展效应的集电结势垒电容模型.将以上势垒电容 模型应用于SiGe HBT频率特性模拟，模拟结果与实验结果符合得很好. 关键词： SiGe HBT 势垒电容 微分电容     

Facile synthesis of nanostructured n-type SiGe alloys with enhanced thermoelectric performance using rapid solidification employing melt spinning followed by spark plasma sintering

SiGe alloy is widely used thermoelectric materials for high temperature thermoelectric generator applications. However, its high thermoelectric performance has been thus far realized only in alloys synthesized employing mechanical alloying techniques, which are time-consuming and employ several materials processing steps. In the current study, for the first time, we report an enhanced thermoelectric figure-of-merit (ZT) ∼ 1.1 at 900 °C in n-type Si₈₀Ge₂₀ nano-alloys, synthesized using a facile and up-scalable methodology consisting of rapid solidification at high optimized cooling rate ∼ 3.4 × 10⁷ K/s, employing melt spinning followed by spark plasma sintering of the resulting nano-crystalline melt-spun ribbons. This enhancement in ZT > 20% over its bulk counterpart, owes its origin to the nano-crystalline microstructure formed at high cooling rates, which results in crystallite size ∼7 nm leading to high density of grain boundaries, which scatter heat-carrying phonons. This abundant scattering resulted in a very low thermal conductivity ∼2.1 Wm⁻¹K⁻¹, which corresponds to ∼50% reduction over its bulk counterpart and is amongst the lowest reported thus far in n-type SiGe alloys. The synthesized samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy, based on which the enhancement in their thermoelectric performance has been discussed.     

SOI SiGe HBT电学性能研究

研究了SOI衬底上SiGe npn异质结晶体管的设计优化.给出了器件基本直流交流特性曲线,分析了与常规SiGeHBT的不同.由于SOI衬底的引入使SOI SiGe HBT成为四端器件,重点研究了衬底偏压对Gummel曲线、输出特性曲线以及雪崩电流的影响.最后仿真实现材料物理参数和几何物理参数对频率特性的改变.结果表明SOI SiGeHBT与常规器件相比具有更大的设计自由度.SOI SiGe HBT的系统分析为毫米波SOI SiGe BiCMOS电路的设计提供了有价值的参考.     

含有本征SiGe层的SiGe异质结双极晶体管集电结耗尽层宽度模型

本文分别建立了含有本征SiGe层的SiGe HBT(异质结双极晶体管)集电结耗尽层各区域的电势、电场分布模型,并在此基础上,建立了集电结耗尽层宽度和延迟时间模型,对该模型进行了模拟仿真,定量地分析了SiGe HBT物理、电学参数对集电结耗尽层宽度和延迟时间的影响,随着基区掺杂浓度和集电结反偏电压的提高,集电结耗尽层延迟时间也随之增大,而随着集电区掺杂浓度的提高和基区Ge组分增加,集电结耗尽层延迟时间随之减小. 关键词： SiGe HBT 集电结耗尽层 延迟时间     

光化学气相淀积SiGe/Si材料的机制分析

本文对光化学气相淀积SiGe/Si过程中气相反应机制和表面反应历程进行了分析和讨论.利用表面反应动力学的有关理论,结合光化学气相淀积的特点,推导出光化学气相淀积SiGe/Si过程中的生长速率和生长压力的关系.并给出该理论结果和实际实验结果的比较.     

Simultaneous optical measurement of Ge-content and carbon doping in strained epitaxial SiGe films

We use a novel analytical technique, previously shown to be able to decouple germanium and boron contents, to measure simultaneously the germanium and carbon contents of a set of carbon-doped epitaxial SiGe films. The method is based on the use of “perturbation functions” to account empirically for the effects that the dopant has upon the fundamental dielectric functions of the material. To demonstrate the technique, a matrix of 10 wafers having variation in both germanium and carbon contents was analyzed. Neglecting the presence of carbon led to large errors in germanium content, whether measured optically or by X-ray diffraction (XRD). However, using the new method the thickness, germanium and carbon contents could be derived together and very good agreement was obtained between measurements on a production-grade optical metrology tool and measurements by secondary ion mass spectrometry (SIMS). To verify the production-worthiness of the approach used, results from two different production metrology tools (i.e. two Therma-Wave Opti-Probe 5220 tools) were compared and some repeatability testing was also performed. The method holds great promise for improving run-to-run process control for advanced epitaxy processes.     

锗硅合金脊形光波导的优化分析与设计

根据脊形光波导的基本设计要求，分析了锗硅合金脊形波导的结构参数对其光传播特性的影响，并优化设计了结构参数，其合理性得到了实验验证。     

SiGe HBT集电结耗尽层渡越时间模型

集电结耗尽层的渡越时间是影响晶体管交流放大系数和频率特性的重要参数。本文分三种情况求解了SiGe HBT集电结耗尽层宽度。建立了不同集电极电流密度下的集电结耗尽层渡越时间模型，该模型考虑了基区扩展效应。利用MATLAB对该模型进行了模拟，定量地研究了集电结反偏电压、集电区掺杂磷或砷的浓度、集电区宽度对集电结耗尽层渡越时间的影响。模拟结果表明：随着集电结反偏电压、集电区掺杂浓度以及集电区宽度的增大，集电结耗尽层渡越时间增大；集电结耗尽层渡越时间对薄基区的SiGe HBT频率特性影响显著，不能忽略。     

多孔硅锗的制备及其近红外发光增强

用激光照射辅助电化学刻蚀硅锗合金样品能够形成多种低维纳米结构。在硅锗合金上形成的多孔状结构在波长为725 nm处有很强的光致发光(PL)峰,PL的增强效应不能单独用量子受限模型来解释。我们提出新的模型来解释这种低维纳米结构的PL增强效应。     

Electroluminescence from Si/SiGe quantum cascade emitters

Intersubband electroluminescence results are presented from Si/SiGe quantum cascade emitters at 3.2 THz and at temperatures up to 150 K. The effect of adding doping into the active quantum wells was studied in addition to reduced barrier widths from previous measurements. While the current through the sample is increased by the addition of doping, the emitted power is reduced through additional free carrier absorption and Coulombic scattering. Free electron laser measurements confirm the intersubband transitions in the quantum wells of the cascade devices and produce non-radiative lifetimes of 20 ps between 4 and 150 K.     

Free-standing Si/SiGe micro- and nano-objects

Free-standing SiGe/Si microtubes, microneedles, helical coils, bridges and submicron vertical rings have been fabricated from elastically strained SiGe/Si heterostructures grown by ultra-high vacuum chemical vapor deposition. Three-dimensional micro- and nano-objects have been formed by self-scrolling after electron beam lithography, reactive ion etching and wet selective etching. Vertical rings with very smooth sidewalls may have applications in hot embossing lithography as well as in microelectronics and micromechanics. By adjusting the SiGe/Si bilayer thickness or Ge concentration, the diameter of tube or ring could be decreased into the nanometer scale.