Lattice reordering in Pb implanted Ge crystals

Channeling effect and sheet resistivity techniques have been used to investigate the damage induced by 40 keV Pb implantation in Ge crystals. At 450° the reordering of the Ge lattice occurs simultaneously to the out-diffusion of the implanted Pb atoms while the recovery of the sheet resistivity occurs at higher temperatures. 90% of the implanted atoms still retained in the crystal are located in substitutional sites. Work supported in part by Centro Siciliano di Fisica Nucleare e di Structura della Materia and by Gruppo Nazionale di Struttura della Materia del Consiglio Nazionale delle Ricerche.     

Diffusion effects in ion implanted germanium

During isochronal anneal sequences the number of Hg, Tl and Bi atoms implanted into Ge has been found to decrease. This decrease occurs for all three species and has been observed for samples implanted at room temperature as well as for hot implants (300—350°C). The decrease starts at anneal temperatures of 350—550°C. Similar results have been obtained for In and Sb implanted Ge. For samples implanted with Hg to doses leading to amorphous layers, the decrease in the number of implanted atoms seems to be related to the reordering of the amorphous layer. The experiments show that no diffusion of the implanted atoms into the bulk material occurs and the decrease observed is attributed to be a diffusion of the atoms to the surface followed by outdiffusion, thermal etching or both.     

Scanning tunneling microscopy identification of atomic-scale intermixing on Si(100) at submonolayer Ge coverages

The positions of Ge atoms intermixed in the Si(100) surface at very low concentration are identified using empty-state imaging in scanning tunneling microscopy. A measurable degree of place exchange occurs at temperatures as low as 330 K. Contrary to earlier conclusions, good differentiation between Si atoms and Ge atoms can be achieved by proper imaging conditions.     

In-beam Mössbauer spectroscopy:57Fe in Si and Ge

Fe has been studied in the semiconductors Si and Ge with the Coulomb excitation recoil implantation technique in a wide temperature range. In the case of Fe inSilicon it was found that one third of the implanted atoms land on interstitial sites. The long range diffusion of these atoms could be observed microscopically at temperatures around 600 K. The isomer shift of interstitial Fe in Si was determined. The remaining atoms exhibit a strong quadrupole splitting on disturbed sites. This component seems to relax into a state with higher symmetry above 700 K. InGermanium a similar situation is found. Whereas iron on disturbed sites dominates the spectra, the direct implantation into interstitial sites is also observed below 200 K. At higher temperatures the substitutional position is preferred. The isomer shifts for interstitial and substitutional Fe in Si and in Ge are in good agreement with calculated electron densities.     

Origin of enhanced Ge interdiffusion at the initial stage of Ge deposition on Si(5 5 12)-2 × 1: Tensile stress induced by substrate chain structures

By combined investigation of STM and synchrotron PES on Ge/Si(5 5 12)-2 × 1 at 530 °C, it has been found that, in addition to the upward-relaxed surface Si atoms, a subsurface Si atom is also readily replaced by an arriving Ge atom at the initial adsorption stage. Such enhanced interdiffusion is due to a unique character of one-dimensional chain structures of the reconstructed substrate, such as π-bonded and honeycomb chains not existing on other low-index Si surfaces such as Si(001)-c(4 × 2) and Si(111)-7 × 7, applying a tensile surface stress to the neighbouring subsurface atoms. Interdiffusion of Ge having lower surface energy induces adsorption of the displaced Si atoms on the surface to form sawtooth-like facets composed of (113)/(335) and (113)/(112) with arriving Ge atoms until the surface is filled with those facets. Such displacive adsorption is the origin of high Si concentration of formed facets.     

The superconducting transition temperature of bulk samples of the niobium-germanium A15-phase after implantation of Ge,Si, O and Ar ions

Bulk material of Nb₃ (Ge_0.8Nb_0.2) with A15 structure and a superconducting transition temperature T_c of 6.5 K has been implanted with Ge, Si, Ar and O ions and subsequently annealed at high temperatures. After annealing between 700 and 750°C the Ge implanted samples showed a strong increase in T_c up to 16.2 K. With Si ions only a T_c of 13 K was obtained, with Ar and O ions T_c remained below 9 K. From X-ray measurements carried out on high T_c Ge implanted samples it could be concluded that the implanted surface layer grows up to a high degree epitaxially on the single crystallites of the bulk material. The lattice constant $\text{a}$₀ of the implanted film was reduced by 0.02 Å with respect to the bulk material. This reduction in $\text{a}$₀ is stronger than expected from the transition temperature of the implanted surface layer.     

Simulations of germanium epitaxial growth on the silicon (1 0 0) surface incorporating intermixing

We present kinetic lattice Monte Carlo simulations of Ge deposition onto a reconstructed Si (1 0 0) surface. We account for the exchange of Ge with Si atoms in the substrate, considering two different exchange mechanisms: a dimer exchange mechanism whereby Ge–Ge dimers on the surface become intermixed with substrate Si atoms, and the exchange of Ge atoms below the surface to relieve misfit strain. We examine how Si–Ge exchange affects the interface between the materials when the growth simulations are done at different temperatures.     

Silicon diffusion through thin tungsten films on silicon,studied with Auger spectroscopy

Silicon out-diffusion through ? 3000 Å tungsten films deposited on silicon by r.f. sputtering was studied using Auger spectroscopy. Silicon first diffuses to the tungsten film surface by grain boundary diffusion and surface migration. The out-diffusion kinetics were most strongly dependent on the thickness of the silicon dioxide layer between tungsten and silicon, and this (native) oxide thickness varied with substrate doping. The out-diffusion rate was independent of tungsten film thickness at 540 Å and 2400 Å. For substrates from which the native oxide was removed by backsputtering just prior to tungsten deposition, no Si out-diffusion to the W film surface was observed until almost the entire film had converted to WSi².     

Behavior of N atoms in atomic-order nitrided Si0.5Ge0.5(1 0 0)

Behavior of N atoms in atomic-order nitrided Si_0.5Ge_0.5(1 0 0) by heat treatment in Ar at 600 °C was investigated by X-ray photoelectron spectroscopy (XPS). For thermal nitridation by NH₃ at 400 °C, nitridation of surface Si atoms tends to proceed preferentially over nitridation of surface Ge atoms. It is also clear that, with the heat treatment, nitridation of Si atoms proceeds by transfer of N atoms from Ge atoms. Angle-resolved XPS results show that Ge fraction beneath the surface nitrided layer increases significantly at 600 °C compared to the initial surface. These results indicate that preferential nitridation of Si atoms at surface over Ge atoms induces Ge segregation beneath the surface nitrided layer at higher temperatures above 400 °C.     

Effects of annealing on ion-implanted Si for interdigitated back contact solar cell

Effects of annealing on the properties of P- and B-implanted Si for interdigitated back contact (IBC) solar cells were investigated with annealing temperature of from 950 to 1050 °C. P-implanted samples annealed at 950 °C were enough to activate dopants and recover the damage by implantation. As the annealing temperature was increased, the diode properties of P-implanted samples were degraded, while that of B-implanted samples were improved. However, in order to activate an implanted B ion, B-implanted samples needed an annealing of above 1000 °C. The implied V_oc of lifetime samples by quasi-steady-state photoconductance decay followed the trend of diode properties on annealing temperature. Finally, IBC cell was fabricated with a two-step annealing at 1050 °C for B of the emitter and 950 °C for P of the front and back surface fields. The IBC cell had V_oc of 618 mV, J_sc of 35.1 mA/cm², FF of 78.8%, and the efficiency of 17.1% without surface texturing.     

SiH4 adsorption on SiGe(0 0 1)

The adsorption process of silane (SiH₄) on a SiGe(0 0 1) surface has been investigated by using infrared absorption spectroscopy in a multiple internal reflection geometry. We have observed that SiH₄ dissociatively adsorbs on a SiGe(0 0 1) surface at room temperature to generate Si and Ge hydrides. The dissociation of Si- and Ge-hydride species is found to strongly depend on the Ge concentration of the SiGe crystal. At a low Ge concentration of 9%, Si monohydride (SiH) and dihydride (SiH₂) are preferentially produced as compared to the higher Si hydride, SiH₃. At higher Ge concentrations of 19%, 36%, on the other hand, monohydrides of SiH and GeH and trihyderide SiH₃ are favorably generated at the initial stage of the adsorption. We interpret that when SiH₄ adsorbs on the SiGe surface, hydrogen atoms released from the SiH₄ molecule stick onto Ge or Si sites to produce Si or Ge monohydrides and the remaining fragments of -SiH₃ adsorb both on Si and Ge sites. The SiH₃ species is readily decomposed to lower hydrides of SiH and SiH₂ by releasing H atoms at low Ge concentrations of 0% and 9%, while the decomposition is suppressed by Ge in cases of 19% and 36%.     

Control of high-k/germanium interface properties through selection of high-k materials and suppression of GeO volatilization

Two approaches to control high-k/Ge interface qualities were investigated. The first approach was using high-k materials that are intimate with Ge. These Ge-intimate high-k materials should have moderate reactivity with Ge to form an amorphized interface that will reduce the interface defects and will suppress the GeO desorption at the interface. The second approach was modifying the annealing processes by using a cap layer to block GeO out-diffusion. We found that Si works as the cap layer very efficiently. By combining those two approaches, we achieved fairly good high-k/Ge metal-insulator-semiconductor (MIS) characteristics with LaYO₃ as the Ge-intimate high-k material, and a NiSi_X electrode as the cap layer. These results provide us an important guide for controlling the high-k/Ge interface properties.     

Si/Gen/Si(001)异质结薄膜的掠入射荧光X射线吸收精细结构研究

利用掠入射荧光X射线吸收精细结构(XAFS)方法研究了在400℃的温度下分子束外延生长的Si/Ge_n/Si(001)异质结薄膜(n=1，2，4和8个原子层)中Ge原子的局域环境结构.结果表明，在1至2个Ge原子层(ML)生长厚度的异质结薄膜中，Ge原子的第一近邻配位主要是Si原子.随着Ge原子层厚度增加到4ML，Ge原子的最近邻配位壳层中的Ge-Ge配位的平均配位数增加到1.3.当Ge原子层厚度增加到8ML时，第一配位壳层中的Ge-Ge配位占的比例只有55%.这表明在400℃的生长条件下，Ge原子有很强的迁移到Si覆盖层的能力.随着Ge层厚度从1 增加到2，4和8ML，Ge原子迁移到Si覆盖层的量由0.5ML分别增加到1.5，2.0和3.0ML.认为在覆盖Si过程中Ge原子的迁移主要是通过产生Ge原子表面偏析来降低表面能和Ge层的应变能. 关键词： XAFS n/Si(001)异质膜')" href="#">Si/Ge_n/Si(001)异质膜 迁移效应     

Structural and magnetic properties of Si1−xGex thin films implanted with Fe ions

A series of Si_1?xGe_x (x = 1, 0.848, 0.591, 0.382, 0.209, 0.064, 0) thin films prepared by ion beam sputtering were implanted with Fe ions to different doses using the metal vapor vacuum arc technique. X-ray absorption fine structure (XAFS) was used to characterize the local microstructure around the Fe atoms in Fe-doped Si_1?xGe_x samples. Structural analysis showed that for annealed samples of Ge-rich thin films (including pure Ge) implanted with low doses of Fe ions, almost all the Fe ions substituted at Ge sites. However, an anti-ferromagnetic Fe₆Ge₅ impurity phase existed in the annealed samples implanted with high doses of Fe. It was also found that the solubility of Fe ions was highest in pure Ge films and that with increasing Si concentration, the solubility decreased. Magnetic analysis showed that for the as-implanted and annealed samples of Ge-rich thin films implanted with Fe ions, room-temperature ferromagnetism was strongest in the pure Ge series of samples and that as the Ge concentration decreased, the ferromagnetism at room temperature weakened. In addition, annealing could increase the number of Fe ions at substitution sites, which resulted in the observed increase in the saturated magnetization after annealing. Experiment and theoretical analysis showed that the ferromagnetism of Fe-doped Ge-rich Si_1?xGe_x thin films samples originated from the s, p–d exchange interactions between the Si_1?xGe_x matrix and those Fe ions which substituted at Ge sites and that the ferromagnetism was mediated by carriers.     

Effect of atomic silicon and germanium beams on the growth kinetics of Si<Subscript>1 – <Emphasis Type="Italic">x</Emphasis></Subscript>Ge<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> layers in Si–GeH<Subscript>4</Subscript> molecular beam epitaxy

The steady-state kinetics of growth of Si_{1 – x} Ge _x layers in one version of hybrid molecular beam epitaxy with a molecular germane source and a sublimating silicon bar has been studied. It has been demonstrated that the processes of capture of hydride molecule radicals by the epitaxial surface and their subsequent decomposition must be taken into account in the analysis of growth kinetics. The comparison of experimental data with the results of kinetic analysis has revealed a close match between them. At low germane pressures \({P_{Ge{H_4}}}\) < 0.5 mTorr, the nature of the growth process is defined exclusively by the specifics of interaction between the molecular beam of Ge monohydride with the growth surface. The influence of the atomic Ge beam from the Si source only manifests at germane pressures exceeding 1 mTorr. Under these conditions, the fluxes of Ge and Si atoms from the sublimating Si source become equal, and the concentration of germyl molecules on the surface reaches saturation. The observed increase in the \({V_{Ge{H_3}}}\) parameter is associated with the activating influence of the flux of silicon atoms from the sublimating source on the decomposition of molecules.     

Dopant diffusion and surface morphology of vanadium implanted 4H-silicon carbide

The diffusion behaviours of vanadium implanted p- and n-type 4H-SiC are investigated by using the secondary ion mass spectrometry (SIMS). Significant redistribution, especially out-diffusion of vanadium towards the sample surface is not observed after 1650℃ annealing for both p- and n-type samples. Atomic force microscopy (AFM) is applied to the characterization of surface morphology, indicating the formation of continuous long furrows running in one direction across the wafer surface after 1650℃ annealing. The surface roughness results from the evaporation and re-deposition of Si species on the surface during annealing. The chemical compositions of sample surface are investigated using x-ray photoelectron spectroscopy (XPS). The results of C 1s and Si 2p core-level spectra are presented in detail to demonstrate the evaporation of Si from the wafer and the deposition of SiO₂ on the sample surface during annealing.     

Determination of deep trap levels in silicon using ion-implantation and CV-measurements

Differential capacitance measurements on Schottky barrier contacts are used to determinedeep energy levels for 29 different impurities implanted into silicon. Back-ground doping and deep levels are separated by making use of the sharply peaked implantation distribution. Donor or acceptor behavior is identified by the shape of the measured apparent charge profile. Energy levels measured for many impurities after annealing of the radiation damage agree with values known from literature. Other levels are caused by a non-thermal state of incorporation into the silicon lattice, e.g. for C, Si, and Ge, even after annealing of the radiation damage. Some impurities, e.g. Nb, Ni, Ti, and Na, show more than one state of incorporation, concentrations of which vary with the annealing conditions. Many implanted elements, especially those having a low solubility, e.g. Au, Be, Co, Se, etc., show strong out-diffusion and precipitation at the surface at annealing temperatures around 500°C.     

Study of Semiconductor Super Thin Heterostructures with Synchrotron Radiation X-Ray Standing Wave Technique

The X ray standing wave experiment method is established with the double-crystal monochromator and precision 2-circle goniometer at Beijing Synchrotron Radiation Facility. It is used combined with the X-ray diffraction, to investigate the heterostructure of super thin Ge atomic layer within Si crystals. The results show that the Ge _x Si_1－x alloy layer with average x=0.13 was formed in the Si crystal sample due to the segregation of Ge atoms during the preparation. Due to the diffusion of Ge atoms to the crystal surface, the Ge_x Si_1－x alloy layer was disappeared and nearly pure Ge layer was formed on the Si crystal surface after annealing at 650℃.     

Hydrogen chemisorption on the 100 (2 × 1) surfaces of Si and Ge

This paper combines a theoretical study of the Si(100) surface having a monolayer of atomic hydrogen chemisorbed to it with an experimental study of the analogous Ge(100) and Ge(110) surfaces. In the theoretical work the underlying (100) silicon surface is taken to be reconstructed according to the Schlier-Farnsworth-Levine pairing model with the hydrogen located on the unfilled tetrahedral bonds of this structure. Self-consistent calculations of the electronic potential, charge density, spectrum, and occupied surface density of states are carried out. The force on the hydrogen atoms is then calculated using the Hellman-Feynman theorem. This force is found to be close to zero, confirming that the hydrogen atoms are indeed at the equilibrium position for the chosen silicon geometry. Features in the calculated photoemission spectrum for the Si(100) 2 × 1 : H surface are discussed in terms of related features in the photoemission spectrum of Si(111) : H, but are found not to agree with the previously measured photoemission spectrum of Si(100) 2 × 1 : H. Measured photoemission and ion-neutralization spectra for Ge(100) 2 × 1 : H agree in their major features with what is calculated for Si(100) 2 × 1 : H, however, suggesting that the Ge(100) 2 × 1 : H surface is reconstricted according to the pairing model. Similarly, measured spectra for clean Ge(100) 2 × 1 agree with calculations for the row dimerized Si(100) surface.     

Photoemission studies of the surfactant-aided growth of Ge on Te-terminated Si(100)

The interactions of Ge adatoms with a Si(100) surface terminated by an ordered layer of Te have been studied in detail using XPS, SXPS, STM and LEED. It has been demonstrated that the Te layer has a surfactant action on the growth mode of the Ge in that the two dimensional growth regime is extended to at least 200 Å and the Te is seen to segregate to the growing Ge surface. The surface reconstruction of the Ge layer changes from (1 × 1) in the initial stages to (2 × 2) as growth proceeds and the surface population of Te is reduced. SXPS line shape analysis has indicated that the initial stages of Ge incorporation are characterised by the formation of small islands above those surface Si sites not fully coordinated with Te. Continued growth of such islands is, however, restricted due to their high surface free energy with respect to the surrounding Te-terminated areas. Ge atoms therefore site-exchange with Te atoms in bridge sites, thus becoming incorporated onto the Si lattice and displacing the Te to bridge sites on the growing surface. In this manner islanding is prevented and two-dimensional growth continues beyond the critical thickness. No evidence is seen for any significant incorporation of the Te within the growing Ge layer.