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Formation of defect states on semiconductor surfaces, at its interfaces with thin films and in semiconductor volumes is usually predetermined by such parameters as semiconductor growth process, surface treatment procedures, passivation, thin film growth kinetics, etc. This paper presents relation between processes leading to formation of defect states and their passivation in Si and GaAs related semiconductors and structures. Special focus is on oxidation kinetics of yttrium stabilized zirconium/SiO2/Si and Sm/GaAs structures. Plasma anodic oxidation of yttrium stabilized zirconium based structures reduced size of polycrystalline silicon blocks localised at thin film/Si interface. Samarium deposited before oxidation on GaAs surface led to elimination of EL2 and/or ELO defects in MOS structures. Consequently, results of successful passivation of deep traps of interface region by CN− atomic group using HCN solutions on oxynitride/Si and double oxide layer/Si structures are presented and discussed. By our knowledge, we are presenting for the first time the utilization of X-ray reflectivity method for determination of both density of SiO2 based multilayer structure and corresponding roughnesses (interfaces and surfaces), respectively.

Hydrogen cyanide (HCN) aqueous solutions can remove copper contaminants from Si surfaces more effectively than hydrochloric acid/hydrogen peroxide mixture (HPM) and sulfuric acid/hydrogen peroxide mixture (SPM). When pH of the HCN solutions is adjusted at 9, Si surface morphology is not changed, while when pH exceeds 10, the Si surfaces are considerably roughed. AFM measurements show that Cu contaminants are present in the form of particles on the bare Si surfaces. XPS measurements show that the particles consist of metallic Cu. The Cu particle height decreases almost linearly with the cleaning time, and the Cu surface concentration decreases exponentially with it. It is concluded that Cu particles gradually dissolve into the HCN aqueous solutions by the direct reaction with cyanide ions at the surface of the Cu particles.

A method of observation of interface states for ultrathin insulating layer/semiconductor interfaces is developed by use of X-ray photoelectron spectroscopy (XPS) measurements under bias. The analysis of the energy shift of the semiconductor core level as a function of the bias voltage gives energy distribution of interface states. When the atomic density of SiO 2 layers is low (e.g., SiO 2 layers formed at 350 °C), only one interface state peak is observed near the midgap, and it is attributed to isolated Si dangling bonds at the interface. For SiO 2 layers with a high atomic density (e.g., SiO 2 layers formed at 700 °C), on the other hand, two interface state peaks, one above and the other below the midgap, are observed, and they are attributed to Si dangling bonds interacting weakly with a Si or oxygen atom in SiO 2 . Interface states can be passivated by cyanide treatment which simply involves the immersion in cyanide solutions such as KCN and HCN solutions. When the cyanide treatment is applied to 〈indium tin oxide/SiO 2 /mat-textured single crystalline Si〉 metal-oxide-semiconductor (MOS) solar cells, the photovoltage is greatly increased, leading to a high conversion efficiency of 16.2%. When the cyanide treatment is performed on polycrystalline Si (poly-Si)-based MOS diodes, a greater effect in comparison to that for single crystalline Si-based MOS diodes is observed due to the elimination of defect states in poly-Si as well as Si/SiO 2 interface states. The cyanide treatment can also increase the conversion efficiency of pn-junction single crystalline and poly-Si solar cells.

A Si cleaning method has been developed by use of potassium cyanide (KCN) dissolved in methanol. When silicon dioxide (SiO2)/Si(1 0 0) specimens with 1014 atom/cm2 order copper (Cu) contaminants are immersed in 0.1 M KCN solutions of methanol at 25 °C, the Cu concentration is reduced to below the detection limit of total X-ray fluorescence spectrometer of ∼3 × 109 atoms/cm2. X-ray photoelectron spectra show that the thickness of the SiO2 layers is unchanged after cleaning with the KCN solutions. 1014 cm−2 order Cu contaminants on the Si surface can also be removed below ∼3 × 109 atoms/cm2, without causing contamination by potassium ions. UV spectra show that Cu-cyano complex ions are formed in the KCN solutions after the cleaning. The main Cu species in the KCN solutions is Cu ( CN ) 4 3 - ions with the concentration of [ Cu ( CN ) 4 3 - ]:[Cu+] = 1:1.6 × 1023. Even when the KCN solutions are contaminated with 64 ppm Cu2+ ions in the solutions, which form Cu ( CN ) 4 3 - ions, the cleaning ability does not decrease, showing that Cu ( CN ) 4 3 - ions are not re-adsorbed. The KCN solutions can also passivate defect states such as Si/SiO2 interface states, leading to the improvement of characteristics of Si devices.

Absract Hydrogen cyanide (HCN) aqueous solutions are found to possess a great ability of removal of copper contaminants on Si as well as a Si defect passivation effect. Copper (Cu) contaminants of 10 13 cm −2 order concentrations can be reduced below 3×10 9 cm −2 taking only 10 s even at room temperature when the pH of the HCN aqueous solution is set at 10. The cleaning ability of HCN solutions increases with pH, indicating that cyanide ions are the reaction species with Cu contaminants. Even when HCN solutions are contaminated with 64 ppm Cu 2+ ions, the cleaning ability is unchanged, indicating avoidance of re-adsorption. Ultraviolet absorption spectra show that after the cleaning, Cu–cyanide complexes are formed in the HCN solutions. The main Cu species in the HCN solutions are Cu ( CN ) 3 2 − , and due to its stability, re-adsorption does not occur. When SiO 2 /Si structure is immersed in the HCN aqueous solutions for 24 h, the SiO 2 thickness is unchanged at all, showing that etching does not occur during the cleaning process. The energy conversion efficiency of pn-junction Si solar cells with a spherical shape is increased to 1.07–1.48 times by immersion in the HCN aqueous solutions, and the improvement is attributed to passivation of defect states in Si by cyanide ions.

The cleaning method using cyanide solutions has been developed to remove heavy metals such as copper (Cu) and nickel (Ni) from Si surfaces. Immersion of Si wafers with both Cu and Ni contaminants in potassium cyanide (KCN) solutions of methanol at room temperature decreases these surface concentrations below the detection limit of total reflection X-ray fluorescence spectroscopy of ∼3×10 9 atoms/cm 2 . UV spectra of the KCN solutions after cleaning of the Cu-contaminated Si surface show that stable copper-cyanide complexes are formed in the solution, leading to the prevention of the re-adsorption of copper in the solutions. From the complex stability constants, it is concluded that the Cu(CN) 4 3− is the most dominant species in the KCN solutions.

Inhibitory effects of fibrinogen on the dynamic surface tension-lowering ability of dipalmitoyl phosphatidylcholine (DPPC)/tyloxapol dispersions at pulsating air/liquid interfaces were investigated. When 10 ppm tyloxapol was added into a 1000 ppm DPPC dispersion prepared by sonication alone, the dynamic surface activity of the mixture was controlled by DPPC and was significantly inhibited by the presence of 1000 ppm fibrinogen. If the added tyloxapol concentration was as high as 100 ppm, tyloxapol then dominated the dynamic adsorption behavior of the dispersion, and the addition of 1000 ppm fibrinogen only showed minor influence on the dynamic surface tension behavior. When a 1000 ppm DPPC dispersion was prepared by sonication with 10 ppm tyloxapol, improved dynamic adsorption behavior resulted and thus the fibrinogen inhibition on the dynamic surface tension-lowering activity of the dispersion was slightly lessened. If the concentration of tyloxapol present during the sonication of a 1000 ppm DPPC dispersion was increased to 100 ppm, less interference by tyloxapol and/or fibrinogen with the dynamic adsorption of DPPC was found, which appears related to the tyloxapol-enhanced DPPC dispersion status with a reduced particle size.

In x Ga 1− x As/GaAs ( x = 0.12–0.23) quantum well (QW) structures were grown by molecular beam epitaxy (MBE) on [001] ridges with various widths (1.1–12 μm) of patterned GaAs (100) substrate. The smallest lateral width of the InGaAs/GaAs quantum wire (QWR) structures was estimated to be about 0.1 μm by high-resolution scanning electron microscope (SEM). The In contents of the grown InGaAs/GaAs QWs on the ridges were studied as a function of ridge top width (ridge width of the MBE grown layer) by cathodoluminescence (CL) measurements at 78 K. Compared to the InGaAs QW grown on a flat substrate, the In content of the InGaAs/GaAs QW on the ridge increases from 0.22 to 0.23 when the ridge top width decreases to about 2.9 μm, but it decreases steeply from 0.23 down to 0.12 with a further decrease of the ridge width from 2.9 to 0.05 μm. A simulation of MBE growth of InGaAs on the [001] ridges shows that this reduced In content for narrow ridges is due to a large migration of Ga atoms to the (100) ridge top region from {110} side facets.

GaAs/AlAs multilayer structures were grown by MBE on patterned GaAs(100) substrates with submicrometre-width ridges in conventional (011) and new (001) directions, and their cross-sectional structures were investigated by TEM. On the (001) ridges, (110) side facets with very good morphology were formed on both sides of the (100) terrace, in contrast with the rather poor morphology of (311)A side facets for the conventional (011) ridge case. GaAs quantum wire (QWR) structures (with a triangular cross section, 26 nm wide by 18 nm high) surrounded by very flat AlAs(110) side facets and a (100) plane were formed on the top of the (100) terrace on the (001) ridges. This indicates that the (001) ridge pattern is highly desirable for fabricating high-quality QWR structures. The migration length of Al atoms on the (100) plane during MBE growth at 570 degrees C was determined for the first time to be 8 nm by TEM observation.

Conductance fluctuations, localization and AB effects in mesoscopic wires and rings of bismuth have been investigated. It is found that the fluctuations from the interference of the holes is much smaller than that from the electrons. The experimental results of conductance correction (ΔGL) from antilocalization effect support the four-probe theoretical formula [1] that it will diverge less than L−1 as the sample length (L) is decreased shorter than the coherent length (Li). The AB effect (h/e oscillation) has been confirmed in some ring samples at 1.5K.

The resistance fluctuations with magnetic field in mesoscopic wires of bismuth have been investigated. The wires show conductance fluctuations (dG) and antilocalization effects, and show voltage fluctuations in Hall measurements at 4.2K and 1.5K. It is found that in the strong spin-orbit coupling case, the dG are reduced by 1 ∼ 2 order, and when the length of wire (L) shorter than the coherence length (Li), the voltage fluctuations are constant, and the conductance fluctuations are not universal and will diverge as dG=(e2/h)LiLt/L2 when the thermal length (Lt) is also shorter than Li.

The influence of tyloxapol on the dynamic surface tension response of dipalmitoyl phosphatidylcholine (DPPC) dispersions at pulsating air/liquid interfaces was investigated. For a 1000 ppm DPPC dispersion prepared by sonication with a larger particle size, the dynamic surface activity of DPPC was strongly affected by the addition of 100 ppm tyloxapol. With a longer sonication time or smaller particle size, the DPPC inactivation was still observed but was somewhat less significant, resulting in slightly lower dynamic surface tensions. If a DPPC dispersion was sonicated in the presence of tyloxapol, the particle size of DPPC was greatly reduced by tyloxapol and the inhibitory effect of tyloxapol on the dynamic adsorption of DPPC may be significantly diminished. The results suggest that the competitive adsorption of tyloxapol may have a detrimental effect on the dynamic surface tension lowering ability of a DPPC dispersion with the extent depending on the DPPC dispersion state. Nevertheless, the dynamic surface activity of DPPC may be enhanced through the improved dispersion by tyloxapol if an appropriate preparation protocol is applied, and the inhibitory effect of tyloxapol may be reduced or overcome. Copyright 2001 Academic Press.

The mechanism of Ni removal from SiO 2 -covered Si specimens by HCN aqueous solutions has been investigated by means of total reflection X-ray fluorescence spectroscopy and X-ray photoelectron spectroscopy measurements. Ni contaminants on the SiO 2 surface are present in the form of SiO-NiOH. The removal mechanism consists of two steps, i.e., an initial fast process followed by a slow process. The rate-determining steps of both the processes are of the first order with respect to the concentration of cyanide ions (CN - ). The fast and slow processes are tentatively attributed to the removal of SiO-NiOH on terraces and in sub-nanometer pores, respectively. The cleaning ability of the HCN aqueous solutions is much better than ammonia aqueous solutions, because of high reactivity to form nickel-cyanide complex ions and avoidance of readsorption of Ni(CN) 2- 4 complex ions in the solutions.

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Hydrogen cyanide (HCN) aqueous solutions can remove copper (Cu) contaminants from SiO 2 surfaces completely even when the cleaning is performed using dilute (e.g., 0.027 wt %) HCN aqueous solutions at 25°C. When pH of the HCN solutions is set at 10, Cu contaminants with a concentration of ∼2 X 10 12 atoms/cm 2 can be removed below ∼3 × 10 9 atoms/cm 2 taking only 10 s. The concentrations of Cu + and [Cu(CN) 2 ] - ions in the HCN solutions drastically decrease with pH, while those of [Cu(CN) 3 ] 2- and [Cu(CN) 4 ] 3- ions increase. The dissociation probability of HCN exponentially increases with pH.Therefore, the improvement of the cleaning ability with pH is attributable to (i) an increase in the concentration of CN - ions, and (ii) the prevention of readsorption due to the formation of stable Cu-cyano complex ions. Measurements of surface Cu concentrations on the SiO 2 surfaces contaminated by the immersion in the CuCl 2 -containing HCN solutions clarify the mechanism of Cu removal. The rate-determining step is a reaction between SiO-CuCN on the surface and CN - ions in the solution to form [Cu(CN) 2 ] - complex ions. The equilibrium constant of this reaction is found to be 4.1 x 10 5 M. This large value shows that desorption of [Cu(CN) 2 ] - proceeds much more easily than adsorption.

We have succeeded in the fabrication of Si-based metal-oxide-semiconductor diodes with an ultrathin (i.e., ∼1.4 nm thick) silicon dioxide (SiO 2 ) layer whose leakage current density is lower than those for thermally grown SiO 2 layers with the same thickness. The leakage current density of the as-grown SiO 2 layers formed in concentrated nitric acid (HNO 3 ) solutions (i.e., ∼3 A/cm 2 at the forward gate bias, V G , of 1 V) is as high as those for thermal SiO 2 layers. The leakage current density is decreased to ∼1.5 and ∼1 A/cm 2 at V G = 1 V by postoxidation annealing (POA) at 400 and 500°C (in hydrogen), respectively, and the decreases are mainly attributed to the elimination of interface states and slow states, respectively. The vibrational frequency of longitudinal optical (LO) phonons of Si-O asymmetric stretching vibration increases with the POA temperature, while that of the transverse optical (TO) phonons remains constant. From the analysis of these vibrational frequencies, the atomic density of the as-grown SiO 2 layer and that after POA at 500°C are estimated to be 2.34 and 2.56 × 10 22 cm 3 , respectively, i.e., higher than that of crystalline SiO 2 bulk of 2.28 × 10 22 cm 3 . Measurements of the valence band spectra for the Si/SiO 2 structure show that the valence band discontinuity energy at the Si/SiO 2 interface is increased from 4.3 to 4.6 eV by POA at 500°C. Therefore, the other reason for the decrease in the leakage current density by POA is a reduction in the tunneling probability through SiO 2 caused by the increase in the band discontinuity energy. Postmetallization annealing treatment at 200°C in hydrogen performed after POA further decreases the leakage current density, showing that atomic hydrogen passivates defect states more effectively than molecular hydrogen.

The low-temperature magnetoresistance of Sb thin films, which were prepared by hot wall epitaxial growth, has been studied. From the comparison of magnetic field dependence of resistance with theories of the two-dimensional (2D) weak localization, it is found that the inelastic scattering time varies as T −1 below 2.5K and as T −.4 above 2.5K, and the inelastic scattering lengths change to small with decreasing thickness.