Electrical characterization studies of p-type Ge,Ge1−ySny,and Si0.09Ge0.882Sn0.028 grown on n-Si substrates

The electrical properties of p-type Ge, Ge_1−ySn_y, and Si_0.09Ge_0.882Sn_0.028 samples grown on n-type Si substrates using ultra-high vacuum chemical vapor deposition have been investigated as a function of temperature. Degenerate parallel conducting layers were found in all Ge/Si, Ge_1−ySn_y/Si, and Si_0.09Ge_0.882Sn_0.028/Si samples, which are believed to be associated with dislocation defects at the interface produced by the lattice mismatch between the two materials. These degenerate conducting layers affect the electrical properties of all the thin epitaxial films. Additionally, temperature dependent Hall-effect measurements show that these materials exhibit a conductivity type change from p to n at around 370–435 K. The mobilities of these samples are generally lower than that of bulk Ge due to carrier scattering near the interface between the epitaxial layer and the Si substrate and also due to alloy scattering. Detailed behavior of temperature-dependent conductivity of these samples is also discussed.     

Magnetic properties of UT2Si2 and UT2Ge2 (T = Co,Ni, Cu) intermetallic systems

Neutron diffraction and magnetization measurements indicate that, at low temperatures, long-range magnetic order is present in UCO₂Si₂, UNi₂Si₂, UCu₂Si₂, UNi₂Ge₂, and UCo₂Ge₂. UCo₂Si₂ and UNi₂Ge₂ are simple collinear antiferromagnets of +-+- type, UCu₂Si₂ a simple collinear ferromagnet. In UNi₂Si₂, a magnetic phase transition from a LSW type structure to collinear antiferromagnetism of +-+- type was found, while in UCu₂Ge₂, the antiferromagnetic structure of ++-- transforms into collinear ferromagnetism. Crystal structure and magnetic parameters are given. No magnetic moment on transition metal ions was found within the accuracy of a powder neutron diffraction experiment. The stability of particular magnetic ordering schemes is discussed in terms of an isotropic RKKY mechanism.     

First-principles calculations of the effect of Ge content on the electronic,mechanical and acoustic properties of Li17Si4-xGex

The electronic, mechanical and acoustic properties of Li₁₇Si_4-xGe_x (x = 0, 2.3, 3.08, 3.53, and 4) have been investigated by using first-principles calculations based on the density functional theory (DFT). The research shows that the bulk modulus B, Young's modulus E, shear modulus G, and hardness H_v gradually decrease with the increasing Ge content. Li₁₇Si_4-xGe_x have the brittle nature from the analysis of B/G ratio and Cauchy pressure. The maximum Young's moduli are all along [1 1 0] plane, and the sequence of degree of anisotropic property is Li₁₇Ge₄ > Li₁₇Si_0.48Ge_3.52 > Li₁₇Si_0.92Ge_3.08 > Li₁₇Si_1.7Ge_2.3 > Li₁₇Si₄. The analysis of acoustic velocity shows that all the sound velocities decrease with the increasing Ge content for Li₁₇Si_4-xGe_x (x = 0, 2.3, 3.08, 3.53, and 4), and the longitudinal wave along [111] direction is fastest for the studied compounds. Debye temperature Θ_D, v_t and v_l decrease with the increasing Ge content. The minimum thermal conductivity decreases with the increasing Ge content, and Li₁₇Si_4-xGe_x have low thermal conductivities and are not potential thermal conductors. The analysis of electronic properties indicates that Li₁₇Si_4-xGe_x have the metal nature and anisotropic electrical conductivity. The electric conduction is improved with the increasing Ge content.     

第一性原理对GenB(n=12—19)团簇的最低能量结构及其电子性质的研究

利用第一性原理在广义梯度近似下，研究了Ge_nB(n=12—19)团簇的结构和电子性质. 结果表明：Ge_nB(n=12—19)团簇具有较大的能隙;这些团簇的最低能量结构包含有Ge₉或Ge₁₀结构单元；B原子嵌套在Ge_n团簇中和B原子替代Ge_n+1团簇的Ge原子是构成Ge_{n 关键词： n}B团簇')" href="#">Ge_nB团簇 最低能量结构 电子性质     

First-principles calculations of the structural,elastic, electronic and optical properties of Si2P2O and Ge2P2O at high pressures

The structures of Si₂P₂O and Ge₂P₂O with the space group Cmc21 are derived. The structural, mechanical, elastic anisotropy, electronic and optoelectronic properties are calculated by first principles calculations based on density functional theory (DFT) with generalized gradient approximation (GGA) at high pressure for Si₂P₂O and Ge₂P₂O. By using the elastic stability criteria, it is shown that their structures are all stable. The phonon dispersion spectra are researched throughout the Brillouin zone as implemented in the CASTEP code, which indicates that the optimized structures are stable dynamically. The brittle/ductile behaviors are assessed in the pressures from 0 GPa to 50 GPa. Our calculations present that the performances of them become ductile with pressure rise. Moreover, the anisotropies of them are discussed by the Young's moduli at different pressure, and the results indicate that the anisotropies of them are obvious. The direct band structures of Ge₂P₂O and the indirect band gap of Si₂P₂O show that Si₂P₂O and Ge₂P₂O present semiconducting character at 0 GPa and 50 GPa. The band structures of Si₂P₂O are changed obviously with the increase of pressure. The total DOS originate mainly from O ‘s’ states, O ‘p’ states, P ‘s’ states and P ‘p’ states and M ‘p’ states (M=Si, Ge). The trends of DOS for Si₂P₂O and Ge₂P₂O display many similarities, and the change of DOS is obviously affected by the pressure for Si₂P₂O. The optoelectronic properties of them are researched. The calculated static dielectric constants, ɛ₁(0), are 3.2 at 0 GPa and 6.4 at 50 GPa for Si₂P₂O, and the values of Ge₂P₂O are 10.2 and 9.2 at 0 GPa and 50 GPa.     

Structure of precipitates and orientation relationships in Al,Ge, Mo-doped higher manganese silicide crystals

Abstract

The structure of Al, Ge, Mo-doped Higher Manganese Silicide (HMS) crystals with the general formulas Mn(Si_0.99Ge_0.01)_1.75, Mn(Si_0.995Ge_0.005)_1.75 and (Mn_0.98Mo_0.02)[(Si_0.98Ge_0.02)_1.75]_0.99Al_0.01 was investigated by scanning and transmission electron microscopy, electron diffraction and X-ray energy dispersive spectrometry in a wide scale range from a few mm to several Å. Several secondary phases were identified in the Mn₄Si₇ matrix: Ge_1?xSi_x (0.1 < x < 0.9) solid solution precipitates with Ge concentration ranging from 5 at. % up to 93 at.%, MoSi₂ platelets, MnSi and Mn₅Si₃ precipitates. Their morphology, structure and crystallographic relationships with the HMS matrix were determined. Mostly local strains in the matrix and precipitates due to lattice misfits at interfaces derived from crystallographic relationships were found two orders of magnitude higher than deformation induced by thermal expansion mismatch. Only a few exceptions of specific relationships were found when the lattice misfit and thermal mismatch have close values. The largest misfit of about 22% was observed between MnSi and Mn₄Si₇ what led to big and numerous cracks in crystals. Therefore, doping can improve the material performance (1) by preventing the formation of MnSi precipitates with metallic properties and (2) by reduction of cracking and crack propagation because of larger MnSi /Mn₄Si₇ lattice misfit compared to Ge_1?xSi_x /Mn₄Si₇ or MoSi₂/Mn₄Si₇ misfits.     

Synchrotron X-ray diffraction and absorption studies of CeM2X2 (M=Cu, Ni and X=Si, Ge) at high pressure

The equations of state of CeCu₂Si₂ and CeCu₂Ge₂ to about 60 GPa, as well as that of CeNi₂Ge₂ to 22 GPa and the valence state of Ce in CeCu₂Ge₂ to 20 GPa have been studied at room temperature in a diamond-anvil cell using synchrotron radiation sources. In each compound, the ambient-pressure phase (tetragonal ThCr₂Si₂-type structure) persisted to the highest pressure studied. The unit cell volumes of CeNi₂Ge₂ at ∼5 GPa and CeCu₂Ge₂ at ∼7 GPa, respectively, approached that of CeCu₂Si₂ taken at ambient pressure. From the equation-of-state data, the bulk modulus was derived to be 112.0±5.1 GPa for CeCu₂Si₂, 125.6±4.3 GPa for CeCu₂Ge₂, and 178.4±14.3 GPa for CeNi₂Ge₂. The valence state of Ce in CeCu₂Ge₂ remained trivalent throughout the pressure range investigated.     

(Si)n/(Ge)n超晶格几何结构

本文用Keating模型计算了Si_1-xGe_x(x=0—1)作衬底、沿(100)方向生长的(Si)_n/(Ge)_n(n=1—6)应力超晶格的几何结构,并讨论了衬底对超晶格生长的影响,计算结果发现对于(Si)_n/(Ge)_n超晶格,用适当的Si_1-xGe_x作衬底有利于超晶格的生长。 关键词：     

Structural,magnetic and electrical properties of some uranium ternary germanides: UM2Ge2 (M = Rh,Ir) and U4M7Ge6 (M = Ru,Os)

The crystal structures and the physical properties of U₄M₇Ge₆ (M = Ru, Os) and UM₂Ge₂ (M = Rh, Ir) have been investigated. The former crystallize in the cubic structure of U₄Re₇Si₆; U₄Ru₇Ge₆ orders ferromagnetically at T_C ≈ 10–13 K whereas U₄Os₇Ge₆ remains paramagnetic down to 4.2 K. The latter whise structures derive from the tetragonal ThCr₂Si₂ or CaBe₂Ge₂ types display limited homogeneity ranges; URh₂Ge₂ exhibits a dense-Kondo behaviour at low temperatures; UIr₂Ge₂ shows polymorphism and its physical properties are strongly influenced by its crystal structure.     

Observation of strain relaxation in Si1-xGex layers by optical and electrical characterisation of a Schottky junction

We have studied the effect of the strain relaxation on the band-edge alignments in a Pt/p-Si_1-xGe_x Schottky junction with x=0.14 by internal photoemission spectroscopy and current–voltage measurements. We have shown that the variations in the band-edge alignments can be observed directly by measuring the optical and electrical properties of a simple Schottky junction. The strain in the Si_1-xGe_x layer has been partially relaxed by thermal treatments at two different temperatures. The degree of relaxation and other structural changes have been determined by a high-resolution X-ray diffractometer. Both optical and electrical techniques have shown that the barrier height of the Pt/Si_0.86Ge_0.14 junction increases with the amount of relaxation in the Si_1-xGe_x layer. This shows that the valence-band edge of the Si_1-xGe_x layer moves away from the Fermi level of the Pt/Si_1-xGe_x junction. The band-edge movement results from the increase in the band gap of the Si_1-xGe_x layer after the strain relaxation. This result agrees with the theoretical predictions for the strain-induced effects on the Si_1-xGe_x band structure. Received: 18 October 2000 / Accepted: 19 December 2000 / Published online: 23 March 2001     

Magnetism,disorder and frustration in heavy-fermion compounds

We examine the magnetic properties of four strongly correlated electron compounds based upon the presence or absence of crystallographic disorder and geometric frustration. All four materials (URu2Si₂, CePd₂Al₃, UNi₄B and URh₂Ge₂) exhibit unusual and not fully understood behavior in their magnetic ordering that are surprising for stoichiometric intermetallic compounds. We summarize these behaviors and relate them to the appearance of disorder and frustration     

First-principles investigations on thermodynamic properties of the ordered and disordered Si0.5Ge0.5 alloys

The structure, formation energy, and thermodynamic properties of Si_0.5Ge_0.5 alloys are investigated through first-principles method. The ordered and disordered structures of Si_0.5Ge_0.5 compounds are considered. Our results show that thermodynamic instabilities of Si_0.5Ge_0.5 alloys at 0 K can be judged from the calculated formation energy. However, the alloy might be prepared at specified environment owing to the entropy effects considered. Moreover, the temperature dependence of the heat capacity, Debye temperature and thermal expansion coefficient of ordered and disordered structures are discussed.     

Europium silicides and germanides of the EuM2X2 type: Crystal structure and the valence states of europium

X-ray diffraction studies of EuM₂X₂ compounds (M = Fe, Co, Ni, Cu; X = Si, Ge) revealed that these compounds crystallize in the ThCr₂Si₂ type body-centered tetragonal structure, with the space group $\text{I4}\text{mmm}$. Distribution of the atoms among the lattice sites, the free parameter of the Si and Ge atoms, and the interatomic distances of the compounds were determined by crystal structure calculations. Europium, as determined by Mössbauer spectroscopy, is present in the di- and tri-valent states in the EuM₂Si₂ compounds, the relative amounts of the two states being different in each of the compounds. In EuNiSi₃, EuNi₂Ge₂ and EuCu₂Ge₂ all the Eu are divalent. The relationship between the structure properties and the valence states of Eu in the compounds is discussed.     

A non-magnetic Fe probe of multiple magnetic phase transitions in RMn2Si2−x Ge x,R=rare earth

Summary Dilute⁵⁷Fe M?ssbauer-spectroscopy studies of RMn₂X₂ (X=Si and/or Ge, R=La, Ce, Pr, Nd, Sm, Eu and Gd) at 4.2 to 650 K yield the following results: Fe in RMn₂X₂ does not carry a magnetic moment. It reveals the magnetic order in the Mn and R sublattices through transferred hyperfine fields (∼100 kOe). The compounds LaMn₂Si₂, LaMn₂Ge₂, CeMn₂Ge₂, PrMn₂Ge₂, NdMn₂Ge₂ and SmMn₂Ge₂, known to be ferromagnets withT _c=300–350 K, are antiferromagnetically ordered above their correspondingT _c. TherT _N values extend from 385 K (SmMn₂Ge₂) to 470 K (LaMn₂Si₂). At the ferromagnetic-antiferromagnetic phase transition, a sharp reorientation of the Mn magnetic moments relative to the crystalline axes occurs. In RMn₂Si_2−x Ge _x with intermediatex values, the Ge is much more dominant in determining the magnetic properties of the Mn sublattice. While PrMn₂Si₂ is an antiferromagnet (T _N=365 K) and PrMn₂Ge₂ is a ferromagnetantiferromagnet (T _c=328 K,T _N=415 K), we find that in PrMn₂SiGe, the magnetic behaviour is similar to that in pure PrMn₂Ge₂,T _c=305 K andT _N=395 K. Paper presented at ICAME-95, Rimini, 10–16 September 1995.     

The stable CaBe2Ge2 structures in antimonide compounds ATM2Sb2 (A = Ca, Sr, Ba; TM = Fe, Co, Ni, Cu): A first-principles study

We have investigated the structural properties of 3d transition metal antimonide compounds ATM₂Sb₂ by first-principles calculations. We find that the calcium-based CaNi₂Sb₂, the strontium-based SrNi₂Sb₂, SrCu₂Sb₂, and the barium-based BaCu₂Sb₂ are stable in the CaBe₂Ge₂-type structure. All the other compounds are stable in the ThCr₂Si₂-type structure. SrCo₂Sb₂ in the ThCr₂Si₂-type structure has specifically ferromagnetic preference. The stable compounds in the CaBe₂Ge₂-type structure have strong interlayer interactions. Although the stable stacking structures are different, all the Fe-based compounds have the stripe-like antiferromagnetic ground states. The Co-based compounds have the ferromagnetic ground states. The Ni-based and Cu-based compounds have the nonmagnetic ground states.     

Stability, structural, elastic, and electronic properties of polymorphs of the superconducting disilicide YIr2Si2

Using the ab initio approaches, the comparative stability, structural, elastic, and electronic properties of three polymorphs of the superconducting disilicide YIr₂Si₂, which differ in the atomic configurations of [Ir₂Si₂] (or [Si₂Ir₂]) blocks, were examined. For these YIr₂Si₂ polymorphs, the optimized structural data, elastic parameters, electronic bands, total and partial densities of states, Fermi surface topology, and chemical bonding were obtained and analyzed. Our studies showed that although ThCr₂Si₂- and CaBe₂Ge₂-type polymorphs are mechanically stable and relatively hard materials with low compressibility, they will behave as ductile systems. Among them, ThCr₂Si₂-type polymorph will show enhanced elastic anisotropy. In the vicinity of the Fermi energy, the topology of the electronic bands and the Fermi surface for various polymorphs are quite different. Besides, the CaBe₂Ge₂-type polymorph is expected to be anisotropic, i.e. happening mainly in the [Si₂Ir₂] blocks. The inter-atomic bonding for YIr₂Si₂ polymorph phases can be described as an anisotropic mixture of covalent, metallic, and ionic contributions, where inside the [Ir₂Si₂] (or [Si₂Ir₂]) blocks, Ir-Si and Ir-Ir bonds take place, whereas between the adjacent [Ir₂Si₂] (or [Si₂Ir₂]) blocks and Y atomic sheets, Si-Si and Ir-Y, Si-Ir and Si-Y, or mainly Ir-Ir bonds emerge for various polymorphs.     

Local and itinerant Magnetism AND Crystal structure of RRh2Ge2 and RRu2Ge2 (r = rare earth)

The compounds RRh₂Ge₂; and RRu₂Ge₂ were synthesized X-ray studies show that they have the expected ThCr₂Si₂; tetragonal-type structure Magnetization studies at 1 8–300 K, ¹⁵¹Eu Mossbauer studies at 4 l, 77 and 300 K and the crystallography studies show the following- All RRh₂Ge₂; like RRh₂Si₂; exhibit two magnetic phase transitions, one corresponding to the antiferromagnetic ordering of the local rare earth moments. T_N = 8–90 K, the other corresponding to the itinerant electron ordering of the Rh sublattice. T_M = 3–9 K The heavy rare earths in RRu₂G₂; order antiferromagnetically and undergo a spin-flop transition in a relatively low magnetic field, <10 kOe The light elements in RRu₂Ge₂; order in a ferromagnetic, somewhat unclear structure NdRu₂Ge₂, like NdRu₂Si₂, exhibits two peaks in the magnetization curves Again, the lower may correspond to itinerant electron ordenng or, alternatively, to spin reorientation of the rare earth sublattice Eu in both EuRh₂Ge₂ and EuRu₂Ge₂ is divalent, whereas Ce in both CeRh₂Ge₂ and CeRu₂Ge₂ is trivalent For all rare earths the ordenng transition in RRh₂Ge₂ is higher than in RRu₂Ge₂. This fact can be associated with the smaller R-R distances in RRh₂Ge₂ and/ or due to the stronger magnetic character of the Rh 4d conduction electrons Companson of the magnetic properties and ¹⁵¹Eu hyperfine interactions of Eu²⁺Rh₂Ge₂, Eu²⁺Ru₂Ge₂, Eu²⁺Rh₂Si₂ and Eu³⁺Ru₂Si₂ with all the other systems leads to the conclusion that the conduction electrons play the dominant role in determining the magnetic properties of these systems Crystal-field effects are also of considerable importance, since the Mossbauer studies yield for the second-order crystal-field parameter A⁰₂〈r²_4f〉 the huge values +385 and +282 K for EuRu₂Ge₂; and EuRh₂Ge₂, respectively The easy axis of magnetization in the Eu compounds is in the basal plane The large second-order crystal field predicts well the direction of the easy axis for all other rare earths No superconductivity has been observed in any of the compounds, down to 1 8 K A companson of the magnetic properties of the germanides with those of the silicides shows great similanties, the differences being accounted for by the different unit cell sizes and c/a ratios.     

New ring-like models and ab initio DFT study of the medium-range structures,energy and electronic properties of GeSe2 glass

Ab initio DFT calculations were performed on Ge_nSe_m nanoclusters (n?=?2, 3, 5, 6, 12; m?=?6–9, 14, 16, 30) that represent the local structure of GeSe₂ glass and on some ‘defect’ Ge_nSe_m clusters that are thought to be related to the inhomogeneity of the structure at the nanoscale. The optimal geometries, total energies and their derivatives as well as the electronic properties of Ge_nSe_m nanoclusters were calculated using traditional DFT method. In addition, the TD-DFT method has been applied to calculate the electronic band gaps of the clusters. The calculated physico-chemical properties of Ge_nSe_m nanoclusters and their couplings with the local-and medium-range order structure formations in GeSe₂ glass are analysed and discussed.     

Spin fluctuation effects in substituted CeRu2Si2 and YbPd2Si2 alloys

Effects of chemical substitution in CeRu₂Si₂, a well-studied heavy fermion system and YbPd₂Si₂ have been investigated through magnetic susceptibility and x-ray diffraction in the systems CeRu _x Si₂, CeRu_2−x Os _x Si₂, CeRu₂Si_2−x Ge _x and YbPd₂Si_2−x Ge _x . Replacing silicon by germanium generates normal chemical pressure effect, namely, Ce and Yb atoms in CeRu₂Si₂ and YbPd₂Si₂ became more and less magnetic respectively. With increasing Ge concentration, CeRu₂Si_2−x Ge _x exhibits larger susceptibility at low temperature, goes to an antiferromagnetic state and finally becomes ferromagnetic. In YbPd₂Si_2−x Ge _x , increasing Ge concentration drives Yb atoms to more divalent state. Electronic effects are more pronounced in CeRu_2−x Os _x Si₂ though CeRu₂Si₂ and CeOs₂Si₂ have very nearly the same lattice parameters. It is conjectured that CeRu₂Si_2−x Ge _x may be the first Ce-based heavy fermion having a magnetic ground state. The authors felicitate Prof. D S Kothari on his eightieth birthday and dedicate this paper to him on this occasion.     

Dopant activation in Sb-implanted relaxed Si1−xGex alloy layers grown on compositionally graded buffers

Supersaturated solid solutions of substitutional, electrically active Sb have been obtained by ion implantation of relaxed epitaxial Si_1?xGe_x alloy layers grown on compositionally graded buffers. Substitutional and nonsubstitutional Sb fractions in relaxed Si_0.85Ge_0.15, Si_0.65Ge_0.35 and Si_0.50Ge_0.50 alloy layers implanted to a dose of 5×10¹⁵ Sb cm^?2 and annealed isothermally at temperatures ranging from 400 to 850°C have been studied by Rutherford backscattering/channeling, transmission electron microscopy and Hall-effect and sheet resistivity measurements. A supersaturated solution of Sb corresponding to a peak carrier concentration of 4×10²⁰ cm^?3 and an electrically active fraction of 40% of the implanted dose is observed by Hall measurements for the case of Si_0.85Ge_0.15 and Si_0.65Ge_0.35 alloys annealed at 550°C.