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.     

2.5 Behaviour of amorphous Ge contacts to monocrystalline silicon

The performance of evaporated amorphous Ge films (thickness $\text{～-500}\text{A}\text{?}$) contacts to etched n-and p-type silicon crystals of different resistivities are discussed. The Ge was 3 Ωcm n-type was also used but gave no difference), and as external contact to the Ge film an Au layer was evaporated. The behaviour of the aGeSi junction seems to be largely governed by interface effects (and thus depends on surface preparation), as is often the case with metal-Si junctions, but Ge gives more reproducible and less time-varying results.In the process of clarifying the function of the contact the following structures were investigated (1) aGe_pⁿSiIn (Hg), where the latter is an ohmic contact, (2) amSi_pⁿSi-metal where amSi is a surface region of the crystal which has been rendered amorphous by ion bombardment, (3) aGe_pⁿSi-metal. I-V and C-V measurements were performed. From the results we conclude that aGeSi junctions act as low-resistance contacts when fed by electron or hole currents from the crystal. The currents (holes and electrons) that are injected into the crystal from the film are limited by barriers to small current densities, usually in the range 10^?6 A cm^?2. It is suggested that the small hole currents are explained by an increase in the hole barrier, effected by positive charges at the interface or in the Ge film, which are built up when positive carriers (holes) are injected by the contact.     

Control of oxidation on NiSix during etching and ashing processes

The oxidation on nickel silicide (NiSi_x) during plasma etching and oxygen ashing is investigated for stable contact resistance on NiSi_x. NiSi_x exposed by various processes is observed by X-ray photoelectron spectroscopy. The oxidation on NiSi_x is promoted by the fluorine that remains during etching and the oxide thickness on n⁺ NiSi_x is greater than that on p⁺ NiSi_x. The remaining fluorine after etching can be decreased by in-situ nitrogen plasma treatment during the post-etching process. Therefore, the oxidation progress with exposure to air and the difference in oxidation on NiSi_x between n⁺ and p⁺ can be suppressed.     

The Distribution of the Energy Gap and Josephson IcRn Product in Bi2Sr2CaCu2O8+x by Tunneling Spectroscopy

We present direct measurements of the density of states by tunneling spectroscopy on slightly overdoped Bi₂Sr₂CaCu₂O_8+x (Bi2212) single crystals at low temperature using break-junction and point-contact techniques. We find that (i) the variation of the gap magnitude, Δ, between 20 and 36 meV is likely to be intrinsic to Bi2212, and (ii) there is a correlation between the maximum value of the Josephson I _c R _n product and the gap magnitude: I _c R _n decreases with the increase of Δ. The maximum I _c R _n value of 26 mV is observed at Δ = 20.5 meV. For Δ = 36.5 meV, the maximum measured value of I _c R _n is 7.3 mV. We conclude that (i) the distribution of the Josephson I _c R _n product as a function of gap magnitude cannot be explained by the presence of a single energy gap in Bi2212, and (ii) the coherence energy scale in Bi2212 has the maximum Josephson strength.     

A new approach to the diagnostics of nanoislands in Ge x Si1 − x /Si heterostructures by secondary ion mass spectrometry

A new approach to the diagnostics of Ge _x Si_{1 ? x} /Si heterostructures with self-assembled nanoislands, which is based on the method of secondary ion mass spectrometry (SIMS) using secondary Ge₂ cluster ions, is discussed. Calibration dependences of the yield of atomic (Ge) and cluster (Ge₂) secondary ions on the concentration of germanium in homogeneous Ge _x Si_{1 ? x} have been obtained for a TOF.SIMS-5 setup. It is established that, in contrast to the well-known linear dependence of ⁷⁴Ge/³⁰Si ∫ x/(1 ? x), the secondary Ge₂ cluster ions obey the quadratic relation Ge₂/³⁰Si ∫ [x/(1 ? x)]². It is shown that the proposed SIMS depth profiling using nonlinear calibration relations for Ge₂ cluster ions provides expanded information on multilayer Ge _x Si_{1 ? x} /Si heterostructures with nanoislands. By using this approach, without additional a priori data on the sample structure, it is possible to distinguish planar layers and GeSi layers with three-dimensional nanoislands, estimate the height of islands, reveal the presence of a wetting layer, and trace the evolution of islands during their formation in a multilayer structure.     

Studies on growth mechanism of HgCdTe epilayer on Si grown by HWE

In this paper, the mechanism of Hg_1−xCd_xTe/Si heterojunction grown by HWE (Hot Well Epitaxy) was studied. Opitical characterizations were shown with FTIR, the composition x = 0.39 was deduced by using MIR transmittance, the absorbing peak at 319.4 cm⁻¹ was measured by FIR transmittance, 319.4 cm⁻¹ confirmed the existence of Si–Te bond of at Si/HgCdTe interfacial layer. The I-V characteristics at both room temperature and 77 K of HgCdTe (n-type)/Si (p-type) heterojunction show that the good p-n heterojunction properties was obtained by using HWE. XRD study confirmed the formation of (111) oriented HgCdTe on (211) Si. Morphology of a cross section observed using EPMA indicates the columnar growth of HgCdTe. An analysis of interfcial layer by EPMA indicated presence of three layers composed of Si + Te, Si + Te + Hg and Si + Te + Cd + Hg. Among them, the most important one is the first layer. The problem of lattice mismatch and the difference of thermal expansion coefficient between Si and CdTe or HgTe may be improved by formation of Si–Te stable chemical bond through bybridization orbital bonding between Si and Te. The second and third layers are formed by evaporation-interdiffusion. Formation of the whole interfacial layer provides the appetency for the growth of (111) Hg_1−xCd_xTe epilayer on (211) Si substrate.     

Dynamics and diffusion mechanism in network forming liquid under high pressure: A new approach

The static and dynamic properties of liquid silica (SiO₂) are investigated by molecular dynamics simulation at temperature of 3200 K and in the 0–25 GPa pressure range. To clarify diffusion mechanism and the anomalous diffusivity under compression, we have traced the time evolution of breakage and formation of the Si–O bond in the basic structural units SiO_x (x = 4, 5, 6). The investigation reveals that atomic diffusion is realized through the transition Si^[n] ↔ Si^[n+1] (Si^[n] means that Si atom has n coordinated oxygens) and the instability of units SiO₅ is the cause of the anomalous diffusivity. Moreover, the transitions Si^[n] ↔ Si^[n+1] are not uniformly distributed but strongly localized in the space. The distribution of coordination units SiO_x in network structure is not uniform but tends to form clusters of SiO₄, SiO₅ and SiO₆ and this is the origin of localization of transitions resulted in the spatially heterogeneous dynamics in liquid SiO_2.     

Local Atomic and Electronic Structure with Magnetism of La0.7Ca0.3Mn1?x Cu x O3 (x=0, 0.03, 0.06, 0.1)

Local atomic and electronic structure with magnetic properties, especially Griffiths phase, of polycrystalline samples La_0.7Ca_0.3Mn_1?x Cu _x O₃ (x=0, 0.03, 0.06, 0.1) have been studied. The X-ray absorption spectra (XAS) of Cu 2p core level prove that the valence state of Cu ions exhibits trivalent state when doping content x≤0.06 and divalent Cu²⁺ ions begin to show for x=0.1. For the valence states of Mn ions, the X-ray photoelectron spectroscopy data show that they are in mixed states of Mn³⁺ and?Mn⁴⁺, and a shift to lower binding energy is observed, which is not attributed to the variation of valence states of Mn ions but the change of crystallographic surroundings, because there is no obvious change detected by X-ray absorption fine structure spectroscopy (XAFS). The Debye-Waller factor (σ ²) of x=0.1 sample is only slightly larger compared to x=0, which may be the origin of enhancement of Griffiths phase observed in the inverse-susceptibility as a function of temperature (H/M～T). The H/M～T curves of Cu doped samples indicate coexistence of FM, AFM and PM phase above Curie temperature?T _C , which may be related to the strong hybridization of O 2p and Mn 3d reflected by O 1s XAS spectra.     

Assortment of technological terms for silicon-germanium thin films in gradient configuration

Phase diagrams have been studied to describe the RF PECVD process for intrinsic-hydrogenated silicon Si:H and silicon-low germanium alloy a-Si_1−xGe_x:H thin films using textured Al substrates that have been overdeposited with n-type amorphous Si:H (n⁺ a-Si:H). UV, vis, IR, atomic force microscopy (AFM), Raman spectroscopy, small angle X-ray and cross-section transmission electron microscopy (TEM) are used to establish the phase diagram. The a-Si:H, a-Si_1−xGe_x and μc-Si:H processes are applied for optimization of triple-junction thin silicon-based n-i-p solar cells.     

Structure and photoelectric properties of Si<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> epilayers

Epitaxial layers of n-type Si_{1 − x} Snx (0 ≤ x ≤ 0.04) solid solution were grown by liquid phase epitaxy from tin-based solution melt confined between two horizontal Si(111) single crystal silicon substrates. The structure of epilayers was determined and the photosensitivity spectra of pSi-nSi_{1 − x} Snx (0 ≤ x ≤ 0.04) structures were studied at various temperatures. It is established that Si_0.96Sn_0.04 films have a perfect single crystal structure with (111) orientation and a subgrain size of 60 nm. The photosensitivity edge of the pSi-nSi_0.96Sn_0.04 structure is shifted to longer wavelengths as compared to that of the pSi-nSi structure. The photosensitivity of the pSi-nSi_0.96Sn_0.04 structure in the impurity absorption range depends on the temperature.     

High throughput production of nanocomposite SiOx powders by plasma spray physical vapor deposition for negative electrode of lithium ion batteries

Nanocomposite Si/SiO_x powders were produced by plasma spray physical vapor deposition (PS-PVD) at a material throughput of 480 g h⁻¹. The powders are fundamentally an aggregate of primary ∼20 nm particles, which are composed of a crystalline Si core and SiO_x shell structure. This is made possible by complete evaporation of raw SiO powders and subsequent rapid condensation of high temperature SiO_x vapors, followed by disproportionation reaction of nucleated SiO_x nanoparticles. When CH₄ was additionally introduced to the PS-PVD, the volume of the core Si increases while reducing potentially the SiO_x shell thickness as a result of the enhanced SiO reduction, although an unfavorable SiC phase emerges when the C/Si molar ratio is greater than 1. As a result of the increased amount of Si active material and reduced source for irreversible capacity, half-cell batteries made of PS-PVD powders with C/Si = 0.25 have exhibited improved initial efficiency and maintenance of capacity as high as 1000 mAh g⁻¹ after 100 cycles at the same time.     

Epitaxial growth of semiconducting β-FeSi2 and its application to light-emitting diodes

In this paper, we review the detailed study of epitaxial growth of β-FeSi₂ films by reactive deposition epitaxy (RDE), multilayer technique and molecular beam epitaxy (MBE). The p- and n-type β-FeSi₂ was formed when it was grown under an Fe-rich and an Si-rich condition, respectively. The maximum electron and hole mobilities of the β-FeSi₂ epitaxial films reached 6900 and 13000 cm²/V·s for the n- and p-type β-FeSi₂, respectively, at around 50 K. Room temperature (RT) 1.6 μm electroluminescence (EL) was realized by optimizing the growth conditions for p-Si/β-FeSi₂ particles/n-Si structures prepared by RDE for β-FeSi₂ and by MBE for Si.     

Investigation of Sb diffusion in amorphous silicon

Amorphous silicon materials and its alloys became extensively used in some technical applications involving large area of the microelectronic and optoelectronic devices. However, the amorphous-crystalline transition, segregation and diffusion processes still have numerous unanswered questions. In this work we study the Sb diffusion into an amorphous Si film by means of Secondary Neutral Mass Spectrometry. Amorphous Si/Si_1−xSb_x/Si tri-layer samples with 5 at% antimony concentration were prepared by direct current magnetron sputtering onto Si substrate at room temperature. Annealing of the samples was performed at different temperatures in vacuum (p<10⁻⁷ mbar) and 100 bar high purity (99.999%) Ar pressure. During annealing a rather slow mixing between the Sb-alloyed and the amorphous Si layers was observed. Supposing concentration independent of diffusion, the evaluated diffusion coefficients are in the range of ∼10⁻²¹ m²s⁻¹ at 550 °C.     

Electrical characterization of 4H–SiC Schottky diodes with a RuO2 and a RuWO x Schottky contacts

Two types of Schottky diodes were prepared on n-type silicon carbide (4H–SiC) substrates by deposition of ruthenium oxide (RuO₂) Schottky contacts or ruthenium tungsten oxide (RuWO _x ) Schottky contacts. The RuO₂/4H–SiC and RuWO _x /4H–SiC Schottky barrier diodes were examined first by current–voltage (I-V) measurements, which confirmed symmetry of the I-V characteristics. The ideality factor (n) is rather high (～1.28/～1.15) at the temperature 300 K, the current of saturation is I _S ～10 pA/～7 pA and the Schottky barrier height is ～1.13 eV/～1.11 eV. After this diagnostic step, the samples were analysed by C-V and standard DLTS methods in the temperature range from 83 K to 450 K. In measured DLTS spectra were identified five deep levels ET1–ET5 (0.27, 0.45, 0.56, 0.58 and 0.85 eV) in RuO₂/4H–SiC Schottky barrier diodes and three deep levels E1–E3 (0.36, 0.38 and 0.69 eV) in RuWO _x /4H–SiC Schottky barrier diodes.     

Electrical properties of Sm-doped bismuth titanate thin films prepared on Si (100) by metalorganic decomposition

Samarium-doped bismuth titanate [Bi_4−xSm_xTi₃O₁₂ (BSmT)] thin films have been grown on n-type Si (100) substrates using metalorganic decomposition and subsequent annealing at 700 °C for 1 h. X-ray diffraction analysis showed layered perovskite structures with a single phase in the films. The current-voltage characteristics displayed ohmic conductivity in the lower voltage range and space-charge-limited conductivity in the higher voltage range. The capacitance-voltage characteristics of Au/BSmT/Si (100) exhibited hysteresis loops due to the ferroelectricity and did not show large carrier injections. The fixed charge density and the surface state density of BSmT films on Si substrate were calculated to be in the range of 10¹¹ cm⁻² and 10¹² cm⁻² eV⁻¹, respectively.     

Magneto-transport and Magnetic Susceptibility of SmFeAsO1−x F x (x=0.0 and 0.20)

We report superconductivity in the SmFeAsO_1?x F _x for the x=0.2 system being synthesized using the single step solid state reaction route. Rietveld analysis of room temperature X-ray diffraction (XRD) data shows the studied samples, SmFeAsO_1?x F _x with x=0.0 and x=0.2, are crystallized in a single phase tetragonal structure with space group P4/nmm. The resistivity measurement shows superconductivity for the x=0.20 sample with T _c (onset) ～51.7 K. The upper critical field, [H _c2(0)] is estimated ～3770 kOe by Ginzburg–Landau (GL) theory. Broadening of superconducting transition in magnetotransport is studied through thermally activated flux flow in an applied field up to 130 kOe. The flux flow activation energy (U/k _B ) is estimated ～1215 K for 1 kOe field. Magnetic measurements exhibited bulk superconductivity with lower critical field (H _c1) of ～1.2 kOe at 2 K. In the normal state, the paramagnetic nature of compound confirms no trace of magnetic impurity, which orders ferromagnetically. AC susceptibility measurements have been carried out for SmFeAsO_0.80F_0.20 sample at various amplitude and frequencies of applied AC drive field. The intergranular critical current density (J _c ) is estimated. Specific heat [C _p (T)] measurement showed an anomaly at around 140 K due to the SDW ordering of Fe, followed by another peak at 5 K corresponding to the antiferromagnetic (AFM) ordering of Sm⁺³ ions in the SmFeAsO compound. Interestingly, the change in entropy (marked by the C _p transition height) at 5 K for Sm⁺³ AFM ordering is heavily reduced in the case of the superconducting SmFeAsO_0.80F_0.20 sample.     

Synthesis and properties of dielectric (HfO2)1 − x (Sc2O3) x films

(HfO₂)_{1 ? x} (Sc₂O₃) _x films have been grown by chemical vapor deposition (CVD) using the volatile complexes hafnium 2,2,6,6-tetramethyl-3,5-heptanedionate (Hf(thd)₄) and scandium 2,2,6,6-tetramethyl-3,5-heptanedionate (Sc(thd)₃) as precursors. The composition and crystal structure of the films containing 1 to 36 at % Sc have been determined. The results demonstrate that, in the composition range 9 to 14 at % scandium, the films are nanocrystalline and consist of an orthorhombic three-component phase, which has not been reported previously. Using Al/(HfO₂)_{1 ? x} (Sc₂O₃) _x /Si test structures, we have determined the dielectric permittivity of the films and the leakage current through the insulator as functions of scandium concentration. The permittivity of the films with the orthorhombic structure reaches k = 42–44, with a leakage current density no higher than ～10^?8 A/cm².     

Repulsive Flux Pinning Force in NbTi/Nb Superconductor/Superconductor Multilayers

Flux pinning characteristics have been investigated for the Nb _x Ti_100-x /Nb(x = 65, 50 and 28) and Nb ₂₈ Ti ₇₂/Nb ₆₅ Ti ₃₅ superconductor(S)/superconductor(S^′) multilayers. The maximum of the pinning force F _{p⊥ max} perpendicular to the layer plane as a function of the structure modulation length λ has a peak in the quasi-two-dimensional region (λ～20 nm). The maximum. values of the F _{p⊥ max} versus λ curve are proportional to the difference of the GL coherence length (ξ _GL ) between the superconductive sublayers S and S^′. The results suggest that the large F _{p⊥ max} in the S/S^′ multilayer is caused by the repulsive pinning force due to Nb layers with larger ξ _GL .     

Fabrication and electrical properties of metal-oxide semiconductor capacitors based on polycrystalline p-CuxO and HfO2/SiO2 high-κ stack gate dielectrics

Polycrystalline p-type Cu_xO films were deposited after the growth of HfO₂ dielectric on Si substrate by pulsed laser deposition, and Cu_xO metal-oxide-semiconductor (MOS) capacitors with HfO₂/SiO₂ stack gate dielectric were primarily fabricated and investigated. X-ray diffraction and X-ray photoelectron spectroscopy were applied to analyze crystalline structure and Cu⁺/Cu²⁺ ratios of Cu_xO films respectively. SiO₂ interlayer formed between the high-κ dielectric and substrate was estimated by the transmission electron microscope. Results of electrical characteristic measurement indicate that the permittivity of HfO₂ is about 22, and the gate leakage current density of MOS capacitor with 11.3 nm HfO₂/SiO₂ stack dielectrics is ∼ 10⁻⁴ A/cm². Results also show that the annealing in N₂ can improve the quality of Cu_xO/HfO₂ interface and thus reduce the gate leakage density.     

Deposition of device quality silicon nitride with ultra high deposition rate (> 7 nm/s) using hot-wire CVD

The application of hot-wire (HW) CVD deposited silicon nitride (SiN_x) as passivating anti-reflection coating on multicrystalline silicon (mc-Si) solar cells is investigated. The highest efficiency reached is 15.7% for SiN_x layers with an N/Si ratio of 1.20 and a high mass density of 2.9 g/cm³. These cell efficiencies are comparable to the reference cells with optimized plasma enhanced (PE) CVD SiN_x even though a very high deposition rate of 3 nm/s is used. Layer characterization showed that the N/Si ratio in the layers determines the structure of the deposited films. And since the volume concentration of Si-atoms in the deposited films is found to be independent of the N/Si ratio the structure of the films is determined by the quantity of incorporated nitrogen. It is found that the process pressure greatly enhances the efficiency of the ammonia decomposition, presumably caused by the higher partial pressure of atomic hydrogen. With this knowledge we increased the deposition rate to a very high 7 nm/s for device quality SiN_x films, much faster than commercial deposition techniques offer [S. von Aichberger, Photon Int. 3 (2004) 40].