Thermodynamic Analysis of Ag_3Ge Phase Formation

In the present work a thermodynamic model is presented for the nucleation of metastable Ag3Ge phase from the undercooled melt in Ag-Ge alloy system. It is shown that under kinetically induced favourable condition, nucleation of a single phase compound with an approximate stoichiometry Ag3Ge has greater affinity for nucleation over Ag and Ge based phases requiring diffusion in the liquid.     

Origin of photoluminescence peaks in Ge–SiO2 thin films

Ge–SiO₂ thin films were prepared by the RF magnetron sputtering technique on p-Si substrates from a Ge–SiO₂ composite target. The as-deposited films were annealed in the temperature range of 300–1000 °C under nitrogen ambience. The structure of films was evaluated by X-ray diffraction, X-ray photoemission spectroscopy and Fourier transform infrared absorption spectroscopy. Results show that the content of Ge and its oxides in the films change with increasing annealing temperature (T_a), the photoluminescence (PL) characteristics are closely dependent on the contents of Ge and its oxides in SiO₂ matrix. The dependence observed strongly suggests that the PL peak at 394 nm is related to the existence of GeO and 580 nm to that of Ge nanocrystal (nc-Ge) in the films.     

Laser-Induced Crystallization of a Si1−x Ge x Microstructure

Laser-induced crystallization of SiGe was investigated using a crystallization technique of pulsed excimer KrF laser irradiation on a-SiGe films that were prepared by plasma-enhanced chemical vapor deposition on quartz. The crystallized SiGe sample was investigated by scanning electronic microscopy (SEM); the SiGe microcrystals are 0.5 m in size and embedded in the a-SiGe:H matrix. Strong photoluminescence with two peaks at 720 and 750 nm was observed at room temperature in the crystallized film, whereas the uncrystallized a-SiGe:H films emit do not emit light in the visible range. This indicates that laser-induced crystallization can be used to improve the luminescence efficiency for Si-based materials.     

Origin of photoluminescence peaks in Ge–SiO2 thin films

Ge–SiO₂ thin films were prepared by the RF magnetron sputtering technique on p–Si substrates from a Ge–SiO₂ composite target. The asdeposited films were annealed in the temperature range of 300–10000C under nitrogen ambience. The structure of films was evaluated by X–ray diffraction, X-ray photoemission spectroscopy and Fourier transform infrared absorption spectroscopy. Results show that the content of Ge and its oxides in thefilms change with increasing annealing temperature (Ta), the photoluminescence (PL) characteristics are closely dependent on the contents of Ge and its oxides in SiO₂ matrix. The dependence observed strongly suggests that the PL peak at 394 nm is related to the existenceof GeO and 580 nm to that of Ge nanocrystal (nc-Ge) in the films. © 2002 Elsevier Science Ltd. All rights reserved.     

Thermodynamic Properties of Si–Ge and Si–Sn Melts

The mixing enthalpies of Si–Ge and Si–Sn liquid alloys were measured in an isoperibolic calorimeter. The results demonstrate that the formation of Si–Ge melts is accompanied by a small heat release, while the formation of Si–Sn melts is an endothermic process. Calculations of the Si activity in Si–Sn melts by Schroeder's equation indicate large positive deviations from Raoult's law.     

Structural properties and Mössbauer spectroscopy of Finemet™ doped with Ge

Structural and magnetic properties of amorphous and crystalline alloys Fe_73.5Cu₁Nb₃B₉Si_13?xGe_{x=1;5;10;13.5} were studied by means of energy dispersive X-rays (SEM + EDX), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Mössbauer spectroscopy (MS), as-quenched (a-q) and after annealing (a). EDX show agreement between the nominal and the measured atomic contents for all alloys. DSC provided three phase transition temperatures of the materials, MS spectra reveal amorphous structure of as-quenched alloys and a mixture of amorphous and crystalline structures of annealed alloys. The XRD spectra of annealed alloys allow us to resolve three crystalline phases of Fe.     

Thermoluminescence study of semiconductor materials SixTe60−x As30Ge10

The effect of gamma irradiation on Si_xTe_60–xAs₃₀Ge₁₀, where x= 5, 12 and 20, has been studied using thermoluminescence (TL). As expected in semiconductor materials, both x=5 and 20 chalcogenides showed a wide TL peak ranging from 80–300 °C. However, these two materials also exhibited a sharp peak at 360 and 380 °C for x = 5 and 20, respectively. On the other hand, the material with x=12 showed very little response to gamma radiation, but if the sample was exposed to ultraviolet light (after being glowed of any TL up to 500°C) and then glowed (called phototransfer-thermoluminescence), several peaks appeared at 80, 180, 300, and 350°C. The x= 5 and 20 samples did not show any response to ultraviolet light. Because the TL response depended on the ratio of Te/Si, it can be concluded that the TL technique can also be used to characterize semiconductor materials, and it would complement other techniques such as electrical conductivity and differential thermal analysis.     

Correlation between deep-level parameters and energy resolution of p-type high purity Ge γ-detectors

A physical basis is presented for the previously reported correlation between deep levels in p-type high purity germanium and the energy resolution of corresponding γ-detectors. Taking account of re-emission of trapped holes at 77 K it is shown that effective hole traps are deeper than about E_v + 0.07 eV. Slowly re-emitting traps may become saturated during detector operation.The detector resolution criterion L ≤ 2 keV is found to correspond with an upper limit of 4.5 × 10⁹ cm⁻³ for the total active copper density. This density criterion is shown to be a reliable basis for the routine DLTS characterisation of high purity germanium production.     

Memory properties of a Ge nanoring MOS device fabricated by pulsed laser deposition

The non-volatile charge-storage properties of memory devices with MOS structure based on Ge nanorings have been studied. The two-dimensional Ge nanorings were prepared on a p-Si(100) matrix by means of pulsed laser deposition (PLD) using the droplet technique combined with rapid annealing. Complete planar nanorings with well-defined sharp inner and outer edges were formed via an elastic self-transformation droplet process, which is probably driven by the lateral strain of the Ge/Si layers and the surface tension in the presence of Ar gas. The low leakage current was attributed to the small roughness and the few interface states in the planar Ge nanorings, and also to the effect of Coulomb blockade preventing injection. A significant threshold-voltage shift of 2.5?V was observed when an operating voltage of 8?V was implemented on the device.     

Generation of Charge Carriers in Uniformly Heated Si–Ge Films Heavily Doped with Titanium

We have studied the generation of charge carriers and development of the electromotive force (emf) in uniformly heated n-type Si–Ge films heavily doped with titanium obtained by chemical-vapor deposition on p-type silicon substrates. A maximum emf value of ～3 mV was observed at temperatures within 500–600 K for dark short-circuit currents ～0.5–1 μA, the value of which increased with the temperature to reach ～3 μA at 800 K.     

Investigation of Ge-Si Atomic Interdiffusion in Ge Nano-dots Multilayer Structure by Double Crystal X-ray Diffraction

The fluctuations of the strained layer in a superlattice or quantum well can broaden the width of satellite peaks in double crystal X-ray diffraction （DCXRD） pattern. It is found that the width of the 0^th peak is directly proportional to the fluctuation of the strained layer if the other related facts are ignored. By this method, the Ge-Si atomic interdiffusion in Ge nano-dots and wetting layers has been investigated by DCXRD. It is found that thermal annealing can activate Ge-Si atomic interdiffusion and the interdiffusion in the nano-dots area is much stronger than that in the wetting layer area. Therefore the fluctuation of the Ge layer decreases and the distribution of Ge atoms becomes homogeneous in the horizontal Ge （GeSi actually） layer, which make the width of the 0^th peak narrow after annealing.     

Electrical properties and phase transition of Ge1−x Sn x Se2.5 thin films

The Ge_1–x Sn _x Se_2.5 system was prepared by melting the correct ratio of high purity elements in quartz evacuated ampoules followed by quenching in ice. It was found that, within the Ge_1–x Sn _x Se_2.5 system, a glassy state can be formed when 0 x 0.4. On increasing x to 0.6 a glassy state could not be obtained, as is confirmed by X-ray diffraction. Differential thermal analysis (DTA) was carried out to study the effect of composition on the stability of amorphous phase. Ge_1–x Sn _x Se_2.5 (where 0 x 0.6) thin films have been prepared by the thermal evaporation technique. The electrical conductivity of the thin films have been studied as a function of composition and film thickness.     

Current-voltage characteristics of Si/Si1 − x Ge x heterodiodes fabricated by direct bonding

We have studied the current-voltage (I–U) characteristics of Si/Si_{1 ? x} Ge _x (0.02 < x < 0.15) heterodiodes fabricated by direct bonding of (111)-oriented n-type single crystal silicon wafers with p-type Si_{1 ? x} Ge _x wafers of the same orientation containing 2–15 at % Ge. An increase in the germanium concentration N _Ge in Si_{1 ? x} Ge _x crystals is accompanied by a growth in the density of crystal lattice defects, which leads to a decrease in the minority carrier lifetime in the base of the heterodiode and an increase in the recombination component of the forward current and in the differential resistance (slope) of the I–U curve. However, for all samples with N _Ge ≤ 15 at %, the I–U curves of Si/Si_{1 ? x} Ge _x heterodiodes are satisfactory in the entire range of current densities (1 mA/cm²–200 A/cm²). This result shows good prospects for using direct bonding technology in the fabrication of Si/Si_{1 ? x} Ge _x heterostructures.     

Ge纳米粒子制备技术的研究进展

Ge纳米粒子由于其小尺寸特性而展现出的良好的光学性能吸引着人们对其不断进行深入探索。综述了Ge纳米粒子的物理和化学制备技术,如分子束外延、氢化物还原锗盐等,并对Ge纳米粒子有代表性的光学特性进行了概述,最后展望了Ge纳米粒子的未来发展方向。     

磁控溅射Ge薄膜的结晶特性研究

采用直流磁控溅射技术制备了不同衬底温度下的Ge单层膜,XRD分析结果表明,当衬底温度低于350℃时Ge膜为非晶结构,高于400℃时开始结晶.并研究了不同尺寸Ge颗粒的Ramah散射谱特征,与晶体Ge的散射谱相比,观察到纳米Ge颗粒Raman散射谱的峰位红移与峰形宽化现象;并根据Raman谱的红移量计算了纳米Ge晶粒的平均尺寸,采用声子限域理论较好地解释了实验结果.     

添加Ge的In_(10)Sb_(10)Ge三元合金热电性能

InSb单晶材料具有相当高的载流子迁移率,因而有良好的电学性能。本文采用缓慢凝固技术制备出In-Sb-Ge三元合金,并在320K到706K的温度范围内测量其热电性能。显微结构观察表明,In-Sb-Ge三元合金的微观组织由嵌入含锗相的锑化铟相组成,这一结果与X射线衍射分析的结果相符。性能测试表明,其晶格热导率在整个温度范围内都非常低,尤其在低温下更低,而载流子热导率随温度的升高,从6.3(W.m-1.K-1)降低到2.4(W.m-1.K-1),在热传输过程中起主要作用。在708K时In10Sb10Ge合金的最高ZT值为0.18。     

水热法制备Ge/SiOx纳米电缆

以混合的氧化锗粉和硅粉为原料,采用水热法在高温高压下制备出具有核-壳同轴结构的Ge／SiOx纳米电缆。扫描和透射电镜研究表明这种Ge／SiOx纳米同轴电缆的产量高,直径分布均匀,长度可达微米级,并证实其为非晶态SiOx包裹Ge内核的核-壳结构。Ge芯线沿着[211]方向生长。Ge／SiOx纳米同轴电缆的生长过程遵循气-液-固和氧化物辅助生长机制,与原料中GeO2与Si的比率有关。     

Ge掺杂ZnO薄膜光学特性的研究

采用射频磁控共溅射法在硅基片上沉积了Ge掺杂ZnO薄膜,所制备的样品具有强蓝光发射和弱黄光发射.通过分析Ge掺入量和退火温度对发光谱的影响,并与相同条件下所沉积的纯ZnO薄膜的发光特性进行比较,结果表明,蓝光发射可能与Ge杂质形成的施主能级有关,弱黄峰可能源于Ge替代Zn空位形成的杂质能级到价带的跃迁复合.     

Ge掺杂碳化硅晶体的生长缺陷

采用物理气相传输法(PVT)制备了2英寸Ge掺杂和非掺SiC晶体, 并使用二次离子质谱仪(SIMS)、显微拉曼光谱(Raman spectra)仪、体式显微镜、激光共聚焦显微镜(LEXT)和高分辨X射线衍射(HRXRD)仪等测试手段对其进行了表征。结果表明, Ge元素可以有效地掺入SiC晶体材料中, 且掺杂浓度达到2.52×10¹⁸/cm³, 伴随生长过程中Ge组份的消耗和泄漏, 掺杂浓度逐渐降低; 生长初期高浓度Ge掺杂会促使6H-SiC向15R-SiC晶型转化, 并随着生长过程中Ge浓度的降低快速地转回6H-SiC稳定生长。用LEXT显微镜观察发现, 生长初期过高的Ge掺杂导致空洞明显增多, 位错密度增加, 掺杂晶体中位错密度较非掺晶体增大一倍。HRXRD分析表明掺Ge能增大SiC晶格常数, 这将有利于提高与外延III族氮化物材料适配度, 并改善器件的性能。