Study of the electrical and optical properties of silicon containing oxygen precipitates

The properties of n-type silicon with oxygen precipitates introduced by three-stage annealing were studied by the electron beam induced current (EBIC) method, deep-level transient spectroscopy (DLTS), and photoluminescence (PL). The presence of extended defects with concentration of ≤10⁹ cm^?3 is revealed by the EBIC method. The concentration of electrically active defects formed in silicon due to oxygen precipitation is estimated from the EBIC contrast and is compared to that obtained from the DLTS data. Comparing the spectra of samples with oxygen precipitates with those of plastically deformed crystals, we can assume that the DLTS and PL spectra of silicon with oxygen precipitates are mainly determined by dislocations.     

硅、锗中氧的低温红外吸收

在6—300K下,利用红外傅里叶光谱仪研究了400—4000cm^-1间的硅、锗中氧的红外吸收。采用高分辨条件时,分辨率可达0.5cm^-1。研究了在低温下利用硅的1106cm^-1吸收峰和锗的855cm^-1吸收峰探测硅和锗氧含量的探测限和误差。若样品厚度为2cm,估计在20K下,硅中氧含量探测限～9.6×10¹⁴氧原子·cm^-3,锗中氧含量探测限～3.0×10¹⁴氧原子·cm^-3。同时,对不同生长条件下直拉锗单晶的氧含量进行了研究,并与用锂沉淀法所求得的锗中氧含量加以比较。对不同氧含量的硅样品的1106cm^-1吸收峰在6—300K的变化进行了观察和讨论。 关键词：     

Precipitation of γ′ phase and helium bubbles during proton and α-particle irradiation of nickel–silicon

Segregation of silicon was induced by light-ion irradiation at elevated temperatures in Ni–8Si specimens. Its occurrence at external surfaces, helium-induced cavities, dislocation loops, coherent twin boundaries, grain boundaries, and precipitate-matrix interfaces has been investigated by transmission electron microscopy. Layers of ordered γ^′ (Ni₃Si) phase were formed at most of these point defect sinks. The behaviour of grain boundary precipitation was found to be exceptional in various respects. In particular, a high rate of precipitation distinguishes grain boundaries from all other kinds of point defect sinks investigated here. This phenomenon of rapid precipitation was found to be adjoined to precipitation-driven grain boundary migration and is attributed to a radiation-induced “discontinuous” precipitate reaction. Observations of helium bubble distributions created during α-particle irradiations at growing dislocation loops and at migrating grain boundaries are also briefly discussed.     

An experimental study of anti-phase boundaries contrast of Fe-Si alloys in superlattice reflexions

Thin foils of ordered alloys of different composition are studied by transmission electron microscopy. The contrast on antiphase boundaries 1/4a ₀ ^′ 〈111〉, 1/2a ₀ ^′ 〈100〉 is compared with contrast theories. It is shown that the dependence of the contrast profile on the deviation parameter from the Bragg reflexion position and the thickness of the foil for oblique boundaries is qualitatively in agreement with the theory. On nearly perpendicular boundaries the observed dependence of contrast is qualitatively the same for higher silicon contents. For lower silicon contents, however, only dark contrast (in the dark field image) is observed for all values of the deviation parameter and foil thickness. This behaviour of nearly perpendicular boundaries at lower silicon contents is explained by the existence of a disordered layer of finite thickness in the boundary. The disordered layer also causes the anomalous contrast of 1/2a ₀ ^′ 〈100〉 boundaries in S₂ reflexions for which zero contrast is predicted by the theory. In contrast to the idealized model of a boundary of this type with disordered second nearest neighbours only, the experiments show also some disorder of the first nearest neighbours. Finally, examples of complicated fringe contrast are shown which can possibly be interpreted as many-beam cases with superlattice and fundamental reflexions excited simultaneously.     

Resistance in sub-μm size GaAs lines

The electrical resistance in GaAs submicron mesa lines have been studied as a function of the line width. Using molecular beam epitaxy two types of conducting layers were made: an n⁺-layer and a two-dimensional electron gas confined to an (AlGa)As/GaAs heterostructure. Processing of the lines was made by photolitography, electron beam litography and ion etching. Resistance data at 77 K and 300 K are discussed for line widths in the interval 0.2 to 5 μm. A size dependent conduction was found and interpreted in terms of geometry induced limitation of the effective conducting path.     

Formation of cubic silicon carbide layers on silicon under the action of continuous and pulsed carbon ion beams

The structure and infrared absorption of cubic silicon carbide (β-SiC) layers produced by the continuous high-dose implantation of carbon ions (C⁺) into silicon (E=40 keV and D=5×10¹⁷ cm⁻²), followed by the processing of the implanted layers with a high-power nanosecond pulsed ion beam (C⁺, τ=50 ns, E=300 keV, and W=1.0–1.5 J/cm²), are investigated. Transmission electron microscopy and electron diffraction data indicate the formation of a coarse-grained polycrystalline β-SiC layer with grain sizes of up to 100 nm. A characteristic feature of such a layer is the dendritic surface morphology, which is explained by crystallization from the melt supercooled well below the melting point of β-SiC.     

Location of self-interstitial atoms in boron-implanted silicon by means of rutherford backscattering of channelled ions

Abstract

For locating self-interstitial atoms in silicon by means of Rutherford backscattering of channelled ions, boron has been implanted at room temperature and at the temperature of liquid nitrogen. The employed implantation doses were 2. 10¹⁴ cm^?2 and 7. 10¹³ cm^?2, respectively. The experiments have been performed at 300 K and at 120 K to reduce ionization-stimulated annealing. The beam of 1.4 MeV He⁺-ions was highly collimated.

To obtain the configuration of implantation-induced self-interstitial atoms symmetry considerations have been performed.

The location experiments presented indicate the existence of isolated self-interstitial atoms in silicon. Under the conditions of these experiments the interstitial atoms assume a (110) split configuration of orthorhombic symmetry.     

A Guided Field for Raman Free Electron Laser Could Be Removed with New Beam Source

A guided field is an important part for focusing the intense beam in Raman free electron laser. A new electron beam source with high brightness of 10¹²A/(m rad)² based on a pseudospark discharge was developed [1]. Numerical simulation showed that the guided field for compact free electron lasers could be removed using the new beam source. An electron beam with 12 kA current and 300 kV voltage was obtained. Self-pinch effect of high current beam was observed, the beam propagates 75 cm with constant diameter of 1.5 mm without guided field.     

Imaging the edge channel structure in a quantum Hall device

In a magnetically quantised two dimensional electron gas (2DEG) of finite dimension, the Landau levels bend up at the boundaries due to the confining potential. Edge channels are formed where these intersect the Fermi level. We have used laser imaging with a spatial resolution of 5 μm to investigate the edge channel structure in a gallium arsenide Hall bar at temperatures between 1.5 K and 150 mK. The beam from an Ar⁺ laser is focused to a small spot on the top surface of the device and the induced Hall photovoltage is measured as a function of the spot position. The size of the photovoltage depends on the potential profile in the device and, at integer Landau level filling factors, is a maximum at the edges. In our device the edge regions turn out to be very wide compared to the magnetic length.     

Relationship between Electrical Activity and Grain Boundary Structural Configuration in Polycrystalline Silicon

Temperature dependent electron beam induced current (EBIC) technique has been applied to investigate the electrical activities of grain boundaries (GBs) in polycrystalline silicon. The GB character, misorientation and orientation of GB plane, were analyzed using a FE-SEM/EBSP/OIM system prior to the EBIC measurements. The EBIC contrasts were found to depend on GB character; low GBs showed weak contrasts compared with general GBs at any temperatures, and also demonstrated to vary at GB irregularities such as boundary steps. These results indicate that electrical properties depend on the orientation of the GB plane as well as the misorientation. On the other hand, there existed less differences in temperature dependence of EBIC contrast irrespective of GB characters. The EBIC contrast decreased with increasing temperature, showed a minimum around 250 K, then increased again with further increasing temperature. The resulting temperature dependence of EBIC contrast probably comes from the combination of two types of recombination processes of carriers. One is related to a shallow level associated with an inherent GB structure, though the exact energy levels also would probably depend on GB structures, and the other to a deep level associated with impurities segregated at GBs, which acts as recombination center.     

Self-organized amorphous material in silicon (0 0 1) by focused ion beam (FIB) system

A method using a focused ion beam (FIB) to prepare a silicon amorphous material is presented. The method involves the redeposition of sputtered material generated during the interaction of the Ga⁺ ion beam with a silicon substrate material. The shape and dimensions of this amorphous material are self-organized and reproducible. The stability of this amorphous material under electron irradiation was investigated in the transmission electron microscopy (TEM). Electron irradiation can induce recrystallization of the amorphous material, resulting in the lateral and vertical growth, starting at an amorphous-crystalline interface, of polysilicon containing defects.     

The effect of HCP on the formation of twin boundaries and dislocations in Ni–Co alloys

In this study, molecular dynamics (MD) was used to simulate the rapid solidification process of Ni₄₇Co₅₃ and Ni₄₈Co₅₂ alloys at a cooling rate of 10¹² K/s. The effects of HCP on the formation of twin boundaries and dislocations in two Ni–Co alloys are studied. It is found that the difference of HCP clusters is the main effect that producing discrepancies on microstructure of two alloys. The number of HCP clusters accounted for 9.23% in Ni₄₇Co₅₃ alloy. They are regularly arranged to form the number of single-layer twin boundaries, and each twin boundary ends in a dislocation. The FCC and HCP structures coexist in the same atomic layers, which is easy to create dislocations. The relatively standard FCC crystal and only 0.32% HCP clusters are formed in Ni₄₈Co₅₂ alloy at 300 K. That small amount of HCP clusters are dispersed on the surface, and cause the formation of dislocation in the border with FCC clusters.     

The adsorption of oxygen on gold

The oxidation of gold has been studied under UHV conditions by AES, XPS, and TDS. The previously reported adsorbed oxygen state, which formed by heating the sample above 600 K in 10^?5 Torr of oxygen and which remained after subsequent heating to 1100 K in vacuo, has been shown to result from the reaction of oxygen with silicon diffusing from the bulk. No oxygen adsorption was detected on a clean sample for oxygen pressures up to 10^?4 Torr and sample temperatures between 300–600 K. Chemisorption of oxygen atoms could be induced by placing a hot platinum filament close to the sample during exposure to oxygen. The activation energy for desorption of this oxygen state was estimated from the thermal desorption spectra to be about 163 kJ mol^?1. The chemisorbed oxygen atoms and the oxygen associated with silicon were distinguished by different O(1s) binding energies (529.2 and 532.3 eV respectively) and by different O(KVV) Auger fine structure.     

Self-oscillating mode of electron beam generation in a source with a grid plasma emitter

Plasma processes and electron beam generation in an electron source with a grid plasma cathode are investigated. Experiments are conducted under the conditions of efficient electron extraction and an intense counter ion flux, which break grid stabilization. It is shown that a rise in the gas pressure and in the emitting plasma potential leads to the plasma potential modulation in the frequency range 10⁴–10⁵ Hz. Under the self-oscillation conditions, an electron beam is obtained with a constant current of up to 16 A and an electron energy modulated up to 100% of the accelerating voltage level (100–300 V). An explanation is given for relaxation self-oscillations arising when the plasma potential grows and for the system’s inertial non-linearity arising when the plasma potential induced by the space charge of the counter ion flux lags behind the current of electron-beam-generated ions.     

Synchrotron-based investigation of iron precipitation in multicrystalline silicon

We report on investigations of the precipitation of iron in block-cast multicrystalline silicon using the techniques of X-ray beam induced current, X-ray fluorescence microscopy and X-ray absorption microspectroscopy. The samples studied were intentionally contaminated with iron and annealed at temperatures between 850 and 1050 ^°C. Annealing at 950 ^°C was found to lead to well detectable iron precipitation inside the grains and at grain boundaries. Small only iron clusters were detected after the 850 ^°C anneal while no iron clusters were found after the 1050 ^°C treatment. X-ray absorption near edge structure analyses of the iron clusters revealed mostly iron silicide and in one case iron oxide. Under the given condition at the beamline, the detection sensitivity for iron was estimated to be 4×10⁷ atoms, corresponding to a spherical FeSi₂ particle of 40 nm radius.     

Twin boundary structure of a superconductive YBa2Cu3O6.9 crystal

An orthorhombic YBa₂Cu₃O_6.9 crystal with Tc=91 K, in which synthetic twins are inevitably contained, is so sensitive to electron irradiation that a structural change easily occurs at the twin boundary, causing the phase transformation from orthorhombic to tetragonal system. We have succeeded in taking images, in which lattice fringes sharply bend at the boundary, using an ultra-high-resolution high-voltage electron microscopy (UHR-HVEM) and the intrinsic structure of the twin boundary could be analyzed to be of oxygen-centered type. The diffraction streak, which is excited only from the boundary region, is explained with help of optical diffraction for a model structure of tilted anti-phase boundary. Atomic knock-on displacements start to occur also in the matrix, being a little apart from the boundary, even at very early stage of electron beam irradiation.Presented at the workshop on High-Voltage and High Resolution Electron Microscopy, February 21–24, 1994, Stuttgart, Germany.     

The Effect of Voltage Bias on the EBIC Contrast Present at Varistor Grain Boundaries

Conductive mode scanning electron microscope (SEM) studies of electrically active grain boundaries in a bismuth + antimony doped zinc oxide based varistor have been carried out using the grain boundary—electron beam induced current (GB-EBIC) configuration. EBIC contrast consistent with negatively charged grain boundary planes flanked by compensating positively charged space-charge regions was found at all the grain boundaries investigated. Grain boundaries showing both type I (symmetric) and type II (asymmetric) EBIC contrast were identified and the effect of an applied voltage bias on the EBIC contrast was studied. It was found that, by applying a small voltage bias of around ±30 mV to a grain boundary showing type I contrast, the EBIC signal on either side of the grain boundary could be suppressed.Equally, when a small voltage bias of appropriate polarity was applied to a grain boundary showing type II contrast, an electrically symmetrical grain boundary barrier structure was restored indicating that these interfaces can show electrical activity in the space-charge regions on both sides of the grain boundary plane and demonstrating a common origin for types I and II contrast.     

Silicon doping of MBE-grown GaAs films

Two concentration ranges of silicon doping in MBE-grown GaAs films have been investigated in some detail. In lightly doped films, with a free-electron concentration of ≈10¹⁶cm^?3, low-temperature photoluminescence spectra have been analysed to develop a model to account for spectral features previously attributed to Ge and Si acceptor levels. In heavily doped films, a maximum free-electron concentration of ≈7×10¹⁸ cm^?3 has been obtained, which is only rather weakly dependent on growth conditions and the nature of the arsenic species (As₂ or As₄). Transmission electron microscopy has shown that no significant precipitation effects occur when higher Si fluxes are used but there is evidence for autocompensation. The maximum PL intensity (300 K) is found at a lower free electron concentration then with Sn-doped films, and is more sharply peaked, but there is no evidence for an anomalous Moss-Burstein shift.     

Fabrication of metal/quantum dot/semiconductor structure on silicon substrate

A fabrication technique and optimal growth conditions are reported to develop a Sb-based quantum dot (QD) structure as a nanostructured III–V semiconductor on a silicon substrate. By using solid-source molecular beam epitaxy, high-density (>10¹⁰ cm⁻²) InGaSb QD structures can be obtained under a low growth temperature, which is compatible for use with Si-CMOS processes. We also proposed the construction of a metal/quantum dot/semiconductor (MDS) structure by using the InGaSb QD on a Si substrate. An infrared light emission with a photon energy of 0.95 eV is successfully observed from the fabricated MDS structure under the current injection conditions. It is expected that a MDS structure using a Sb-based QD will be used as a small-sized infrared light source for silicon photonic technology.     

Edge electroluminescence of single-crystal silicon at 80 K: Structures based on a high-efficiency solar cell

The spectral, kinetic, and energy characteristics of edge luminescence of silicon light-emitting diodes (LEDs) with radiating surface area of 0.055 cm² are studied at a temperature of 80 K over a wide range of pulsed currents. The LEDs are fabricated by cutting a high-efficiency solar cell. In contrast to a number of less effective silicon LEDs studied earlier, the external quantum efficiency of our LEDs at a fixed current at 80 K is higher than that at 300 K and its maximum value is about 0.4%. Despite the occurrence of Auger recombination, a record-high emissive power per unit surface area P = 0.2 W/cm² is attained at a pulsed current of 12 A. It is shown that this record value is achieved largely because the mechanism of radiative recombination is changed at large currents. The conditions are analyzed under which the free-exciton luminescence is changed to electron-hole plasma luminescence.