Beiträge zu den Niveauschemata der Ge-Isotope71Ge,73Ge,74Ge und75Ge aus der Untersuchung von (n, γ)-Reaktionen in natürlichem Germanium

Low energy γ-spectra from neutron capture in natural germanium have been studied with several high resolution Ge(Li)-detectors. Measurements have been made with two different target configurations. In the first measurement a normal Ge-target was irradiated with neutrons; no neutrons were allowed to enter the Ge(Li)-detector. In the second measurement the Ge(Li)-detector was used simultaneously as target and as γ- ande ^?-detector. By combination of the results convertion coefficients of several transitions in⁷³Ge have been determined. Several unknown low energy transitions in Ge isotopes have been found with the aid of the second method. The level schemes of⁷¹Ge,⁷³Ge,⁷⁴Ge and⁷⁵Ge have been revised by means of coincidence measurements with a Ge(Li)-Ge(Li)-coincidence system of high efficiency and resolution.     

Electrical properties of Al/p–Ge and Al/Methyl Green/p–Ge diodes

Methyl green (MG) film has been grown for the first time on p–Ge semiconductor using a simple and low-cost drop coating method. The current–voltage (I–V) characteristics of Al/p–Ge and Al/MG/p–Ge diodes have been investigated in the temperature range of 20–300 K. A potential barrier height as high as 0.82 eV has been achieved for Al/MG/p–Ge diode, which has high rectification rate, at room temperature. It is seen that the barrier height of the Al/MG/p–Ge diode at the room temperature is larger than that of Al/p–Ge diode and ideality factor value of 1.14 calculated for Al/MG/p–Ge diode is lower than Al/p–Ge diode. The temperature coefficient of barrier height of the Al/MG/p–Ge diode has been calculated as 2.6 meV/K. The evaluation of current–voltage characteristics shows that the barrier height of the diode increases with the increasing temperature.     

A non‐destructive approach for doping profiles characterization by micro‐Raman spectroscopy: the case of B‐implanted Ge

B‐implanted Ge samples have been investigated by micro‐Raman spectroscopy under different excitation wavelengths, with the aim of gaining insights about the B distribution at different depths beneath the sample surface. The intensities, observed under the different excitation wavelengths, of the B–Ge Raman peak at about 545 cm⁻¹, which is due to the local vibrational mode of the substitutional B atoms in the Ge matrix, have been used to calibrate the optical absorption lengths in B‐implanted Ge. Then, by using these calibrated values, a very sharp correlation between the spectral features of the Ge–Ge Raman peak at ~300 cm⁻¹ and the content of substitutional B atoms has been derived. Accordingly, a non‐destructive approach, based on micro‐Raman spectroscopy under different excitation wavelengths, is presented to estimate, at least at the lowest depths, the carrier concentration profiles from the spectral features of the Ge–Ge Raman peak. Copyright © 2014 John Wiley & Sons, Ltd.     

Structure and optical properties of GeGaS films deposited by thermal evaporation

Amorphous GeGaS thin films have been successfully deposited onto glass slides at room temperature by the thermal evaporation technique. The structural units of the films were studied using Raman spectroscopy. In addition to the basic structural units of GeS₄ tetrahedra, there are some SS and GeGe homopolar bonds which exist in the films. The increase in Ge atoms leads to the replacement of SS bonds by GeGe bonds, and the isolated Ge(Ga)S₄ tetrahedra units transform into corner-sharing or edge-sharing Ge(Ga)S₄ tetrahedra units in the films. The refractive index and optical band gap were derived from transmission spectra of films. The values of optical band gap decrease while the refractive indices increase with increasing Ge content. Composition dependence of optical band gap and refractive index has also been interpreted in terms of the variation in the structure of films based on Raman spectra.     

Ge(SiO2)n团簇结构和电子性质的密度泛函理论研究

采用密度泛函理论中的广义梯度近似(GGA)对Ge(SiO2)n (n = 1—7)团簇的几何构型进行优化,并对能量、频率和电子性质进行了计算。 结果表明,Ge(SiO2)n的最低能量结构是在(SiO2)n端位O原子以及近邻端位O原子的Si原子上吸附一个Ge原子优化得到;随着锗原子数的增加,增加的锗原子易与原来的锗原子形成锗团簇。掺杂锗原子后团簇的能隙比(SiO2)n团簇的能隙小,当多个Ge原子掺杂到(SiO2)3团簇时,其能隙随着Ge原子个数的增加出现了振荡,Gem(SiO2)3的能隙从可见光区到近红外光区变化。二阶能量差分、分裂能表明Ge(SiO2)2和Ge(SiO2)5团簇是稳定的。     

An interface study of crystalline Fe/Ge multilayers grown by molecular beam epitaxy

Fe/Ge multilayers were grown on single crystal Ge(0 0 1) substrates by molecular beam epitaxy. The structural, electronic and magnetic properties of Fe/Ge have been studied. The analysis shows that Fe grows in a layer-by-layer epitaxial growth mode on Ge(0 0 1) substrates at 150 °C and no intermixing has been observed. Growth of a crystalline Ge film at 150 °C on a single crystal Fe film has been observed. At this temperature Ge films grow by means of the island growth mode according to reflection of high energy electron diffraction patterns. Fe layers of 36 nm thickness, deposited at 150 °C on Ge(0 0 1) substrates, show two magnetization reversal values indicating the growth of Fe in two different crystal orientations. 36 nm thick Fe and Ge layers grown at 150 °C in Ge/Fe/Ge/Fe/Ge(0 0 1) sequence shows ferromagnetic behavior, however, the same structure grown at 200 °C shows paramagnetic behavior.     

Molecular beam epitaxy growth of GaAs on an offcut Ge substrate

Molecular beam epitaxy growth of GaAs on an offcut Ge (100) substrate has been systemically investigated. A high quality GaAs/Ge interface and GaAs film on Ge have been achieved. High temperature annealing before GaAs deposition is found to be indispensable to avoid anti-phase domains. The quality of the GaAs film is found to strongly depend on the GaAs/Ge interface and the beginning of GaAs deposition. The reason why both high temperature annealing and GaAs growth temperature can affect epitaxial GaAs film quality is discussed. High quality In_0.17Ga_0.83As/GaAs strained quantum wells have also been achieved on a Ge substrate. Samples show flat surface morphology and narrow photoluminescence line width compared with the same structure sample grown on a GaAs substrate. These results indicate a large application potential for III--V compound semiconductor optoelectronic devices on Ge substrates.     

高温处理工艺对低压MOCVD外延GaAs/Ge太阳电池的影响

采用自制的低压金属有机化学汽相淀积LP-MOCVD设备,在Ge衬底(100)面向(111)偏9°外延生长出GaAs电池结构,对电池材料进行了X射线衍射分析另外,对由此材料制成的太阳电池进行了性能测试,测试结果表明,Ge衬底的高温处理工艺对GaAs/Ge太阳电池的电流电压特性有一定的影响试验表明,在600～700℃之间高温处理效果较好。     

Violet luminescence in Ge nanocrystals/Ge oxide structures formed by dry oxidation of polycrystalline SiGe

Nanocrystals of Ge surrounded by a germanium oxide matrix have been formed by dry thermal oxidation of polycrystalline SiGe layers. Violet (3.16 eV) luminescence emission is observed when Ge nanocrystals, formed by the oxidation of the Ge segregated during the oxidation of the SiGe layer, are present, and vanishes when all the Ge has been oxidized forming GeO₂. Based on the evolution of the luminescence intensity and the structure of the oxidized layer with the oxidation time, the recombination of excitons inside the nanocrystals and the presence of defects in the bulk oxide matrix are ruled out as sources of the luminescence. The luminescence is attributed to recombination in defects at the Ge sub-oxide interface between the Ge nanocrystals and the surrounding oxide matrix, which is GeO₂.     

Theoretical analysis of fluorine-passivated germanium surface for high-k/Ge gate stack by molecular orbital method

Energy state and coordination of fluorine (F)-passivated Ge surface have been theoretically analyzed by semi-empirical molecular orbital method in comparison with hydrogen-passivated Ge surface to predict usefulness of F for passivation element and surface stabilization. Heat of formation for the reaction of F atoms and Ge layer system decreased simultaneously without energy barrier. Resultantly, F-Ge bonds were formed on Ge layer system and Ge surface dangling bonds were passivated by F dissimilar to the reaction of H atoms and Ge layer system. Furthermore, it was confirmed experimentally that the electrical properties of HfO₂/Ge gate stack were improved by F₂-ambient treatment of Ge substrate prior to HfO₂ deposition. It is concluded that F-passivation of Ge surface is useful in making stable and low-defective Ge substrate for high-k dielectric layer deposition.     

Metallurgical behaviour of Ni/AuGe ohmic contacts to GaAs

Auger depth profiling and contact resistance measurements have been used to study sintered Ni/Au/AuGe and Ni/AuGe contacts to GaAs. The results indicate that Ge incorporation is by a process of solid state diffusion rather than by the eutectic melting-recrystallization mechanism found in AuGe contacts. In spite of the improvement in the homogeneity of the contact brought about by using Ni, the thermal stability of these contacts is found to be worse than the simple AuGe ones.     

Features of atomic processes at the formation of a wetting layer and nucleation of three-dimensional Ge islands on Si(111) and Si(100) surfaces

The intermediate stages of the formation of a Ge wetting layer on Si(111) and Si(100) surfaces under quasiequilibrium grow conditions have been studied by means of scanning tunneling microscopy. The redistribution of Ge atoms and relaxation of mismatch stresses through the formation of surface structures of decreased density and faces different from the substrate orientation have been revealed. The sites of the nucleation of new three-dimensional Ge islands after the formation of the wetting layer have been analyzed. Both fundamental differences and common tendencies of atomic processes at the formation of wetting layers on Si(111) and Si(100) surfaces have been demonstrated. The density of three-dimensional nuclei on the Si(111) surface is determined by changed conditions for the surface diffusion of Ge adatoms after change in the surface structure. Transition to three-dimensional growth on the Si(100) surface is determined by the nucleation of single {105} faces on the rough Ge(100) surface.     

Compton profile study of V3Ge and Cr3Ge

In this paper the results of a Compton profile study of two polycrystalline A15 compounds, namely, V₃Ge and Cr₃Ge, have been reported. The measurements have been performed using 59.54 keV γ-rays from an ²⁴¹Am source. The theoretical Compton profiles have been computed for both the compounds using ab-initio linear combination of atomic orbitals (LCAO) method employing CRYSTAL98. For both the A15 compounds, the isotropic experimental profiles are found to be in good overall agreement with the calculations. The comparison points out residual differences in V₃Ge whereas for Cr₃Ge the differences are within experimental error. The behaviour of valence electrons in the two iso-structural compounds has been examined on the scale of Fermi momentum. The valence electron distribution seems to be dominated by the metallic constituents rather than Ge and two compounds show covalent nature of bonding which is larger in V₃Ge compared to Cr₃Ge.      

Light absorption in Ge nanoclusters embedded in SiO2: comparison between magnetron sputtering and sol–gel synthesis

SiGeO films have been produced by a sol–gel derived approach and by magnetron sputtering deposition. Post-thermal annealing of SiGeO films in forming gas or nitrogen atmosphere between 600 and 900 °C ensured the phase separation of the SiGeO films and synthesis and growth of Ge nanoclusters (NCs) embedded in SiO₂. Rutherford backscattering spectrometry analysis evidenced a similar Ge concentration (~12 %), but a different Ge out-diffusion after annealing between the two types of techniques with the formation of a pure SiO₂ surface layer (~30 nm thick) in sol–gel samples. The thermal evolution of Ge NCs has been followed by transmission electron microscopy and Raman analysis. In both samples, Ge NCs form with similar size increase (from ~3 up to ~7 nm) and with a concomitant amorphous to crystalline transition in the 600–800 °C temperature range. Despite a similar Ge concentration, a significant lower NCs density is observed in sol–gel samples attributed to an incomplete precipitation of Ge, which probably remains still dispersed in the matrix. The optical absorption of Ge NCs has been measured by spectrophotometry analyses. Ge NCs produced by the sol–gel method evidence an optical band gap of around 2 eV, larger than that of NCs produced by sputtering (~1.5 eV). These data are presented and discussed also considering the promising implications of a low-cost sol–gel based technique towards the fabrication of light harvesting devices based on Ge nanostructures.     

In situ monitoring of nucleation and evolution of Ge nanodots on faintly oxidized Si(1 1 1) surfaces

We have investigated the nucleation and evolution of germanium (Ge) nanodot (ND)s taking place while depositing Ge onto the silicon (Si) (1 1 1) surfaces with ultra-thin Si oxide films by using ultra-high vacuum in situ high-resolution transmission electron microscopy in the profile-imaging geometry. Various types of growth phenomena such as nucleation, growth and coalescence of Ge NDs have successfully been observed. The results show that the growth phenomena of the Ge NDs are dramatically rapid after their size reaches the size of the critical nucleus. The critical nucleus size estimated from a model using the cohesive energy of the Ge NDs has been consistent with observed one.     

Synthesis of Ge nanocrystals by atom beam sputtering and subsequent rapid thermal annealing

Ge nanocrystals embedded in an SiO₂ matrix were prepared by the atom beam co-sputtering (ABS) method from a composite target of Ge and SiO₂. The as-deposited films were rapid thermally annealed at the temperatures 700 and 800 °C in nitrogen ambience. The structure of the films was evaluated by using X-ray diffraction (XRD) and Raman spectroscopy. XRD results reveal that as-deposited films are amorphous in nature whereas annealed samples show crystalline nature. Raman scattering spectra showed a peak of Ge–Ge vibrational mode shifted downwards to 297 cm^?1, presumably caused by quantum confinement of phonons in the Ge nanocrystals. Rutherford backscattering spectrometry has been used to measure the thickness and Ge composition of the composite films. Size variation of Ge nanocrystals with annealing temperature has been discussed. The advantages of ABS over other methods are highlighted.     

室温下Ge(111)表面原子的协调运动

用扫描隧道显微镜观察了Ge(111)表面的由快速降温至室温而保留下来的中温相.发现除了单个Ge增原子的扩散运动外,主要的运动是发生在畴界上的Ge增原子列的开环和闭环协调运动.从实验上证实了这种最近引起很大实验和理论兴趣的运动方式.通过观察又提出了有待进一步实验和理论研究的问题.     

急冷Al-lat%Ge过饱和固溶体合金的正常-超导转变特性

本文研究了急冷Al-1at%Ge过饱和固溶体合金的结构和正常-超导转变特性。X射线结构分析表明,样品为单一的过饱和α-Al(Ge)固溶体。电阻-温度测量指出,急冷过饱和α-Al(Ge)合金的T_c≈1.44K,高于纯Al的T_c。 关键词：     

The microstructure of vertically coupled quantum dots ensembles by EXAFS spectroscopy

The microstructure of samples containing Ge/Si, GaN/AlN, and InAs/AlAs (Ge, GaN, and InAs quantum dots (QDs) in the Si, AlN, and AlAs matrices, respectively) multilayer heterostructures has been investigated by EXAFS spectroscopy. The effect of the effective thicknesses of Si (or AlN) barrier layers, number of Ge (or GaN) layers in a sandwich, and annealing temperature on the size and shape of Ge (or GaN) clusters, interfacial diffusion in these systems, and formation of three-dimensional ordered ensembles of QDs has been established.     

Microstructural,chemical bonding,stress development and charge storage characteristics of Ge nanocrystals embedded in hafnium oxide

We have grown Ge nanocrystals (NCs) (4.0–9.0 nm in diameter) embedded in high-k HfO₂ matrix for applications in floating gate memory devices. X-ray photoelectron spectroscopy has been used to probe the local chemical bonding of Ge NCs. The analysis of Ge–Ge phonon vibration using Raman spectroscopy has shown the formation of compressively stressed Ge NCs in HfO₂ matrix. Frequency dependent electrical properties of HfO₂/Ge-NCs in HfO₂/HfO₂ sandwich structures have been studied. An anticlockwise hysteresis in the capacitance–voltage characteristics suggests electron injection and trapping in embedded Ge NCs. The role of interface states and deep traps in the devices has been thoroughly examined and has been shown to be negligible on the overall device performance.