Influence of sputtering conditions and electron energy on XPS depth profiling of Ge in SiO2

Ge nanocluster formation in SiO₂ is of growing interest for new electronic applications. Ion beam synthesis using high‐energy Ge implantation connected with thermal annealing is one possible preparation method of such clusters. In addition to investigations of electrical and structural changes during the cluster formation process we also studied chemical changes in the samples using x‐ray photoelectron spectroscopy (XPS). This was done with low‐energy noble gas ion sputtering for depth profiling. Binding state information one can get from the XPS data by means of factor analysis (FA) in combination with other structural investigations. However, mixed bonding states probably created by ion beam damage during sputter erosion are dominating the results. It is shown, that by changing the experimental conditions (ion beam impact depth during sputtering, electron information depth during XPS measurement) these mixed states are influenced in an appropriate manner. It is concluded that useful chemical information on the behavior of the implanted Ge can be derived despite of the ion beam damage. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Auger depth profiling of BaTiO3 ceramics

We investigated the sputter depth profiling of BaTiO₃ by means of Auger Electron Spectroscopy. A quantitative analysis was done for ceramic and single crystal material. Sputtering yield for 2 and 3 keV Ar⁺ ions was determined. For under UHV conditions fractured specimens no preferential sputtering was found. Mechanically polished or contaminated ceramic specimens show preferential sputtering of Ba or Ti. Using sputtering – heating cycles we succeeded in preparing non-contaminated but ion beam mixed surfaces which are stable upto 150 °C.     

Effect of electron irradiation on Na-K silicate glass investigated using X-ray photoelectron spectroscopy and pattern recognition method

Alkali silicate glasses and melts play an important role in material science. Electron interaction with glasses is important for radioactive waste deposition, where electrons of various energies lead to irreversible changes. These changes are caused mainly by ionization and ballistic interaction of electrons with atoms, introducing structural disorder, changes in atomic composition and chemical state, accompanied by alkali ions diffusion. The Na-K silicate glass (5Na₂O · 10K₂O · 85SiO₂), pristine and electron irradiated (doses from 25 C m⁻² to 20 236 C m⁻²) are investigated using X-ray photoelectron spectroscopy (XPS) and the pattern recognition (PR) and fitting procedures. Changes of composition and chemical state of atoms dependent on electron dose are analyzed. At low doses (100-300 C m⁻²), decrease followed by increase of O and Si concentrations was observed. Surface segregation, probable desorption, and in-bulk diffusion of K and Na ions (doses of about 50 C m⁻² and 2000 C m⁻², respectively) were observed. This was accompanied by changes in the chemical state of K atom, where with an electron dose increasing content of elemental K form accompanied by decreasing potassium peroxide form were observed. No difference in chemical state of Si and O atoms was visible under electron irradiation dose to 20 236 C m⁻², within the sensitivity of the applied method.     

Detection of boron and carbon in flux grown single crystals of hexagonal ferrites using electron energy loss spectroscopy

A method of detecting boron and carbon in the lattice of the flux grown single crystals of hexagonal ferrites using Electron Energy Loss Spectroscopy is given. Our results have led us to conclude that these elements are present as a solid solution and not as inclusions.     

Characterizations of a-Se based photodetectors using X-ray photoelectron spectroscopy and Raman spectroscopy

The ‘PLUMBICON’ was one of the first successful imaging tubes using amorphous selenium (a-Se) and many followed. Significant properties of a-Se based imaging tubes have been rediscovered through the invention of the ‘HARP (high-gain avalanche rushing amorphous photoconductor)’, but its operational mechanism and the physics, however are yet poorly described. Previously, we have fabricated photodetectors using nitrogen (N)-doped diamond as a cold cathode and a-Se as a photoconducting target, which successfully responded to light illumination, The device performance,in this case, deteriorates after continuous use largely due to the degradation of a-Se. In this paper, a-Se and amorphous arsenic selenide (a-As₂Se₃) films have been deposited Stoichiometry has been determined by XPS (X-ray photoelectron spectroscopy) followed by Raman spectroscopy characterization. We have found that even an extremely weak incident laser power causes sample degradation during signal accumulation. We speculate that either the incident laser itself and/or the temperature rise due to illumination causes the phase transition in a-Se films. In addition, when As is added into the film, the phase transition leading the degradation is hardly observed, implying that As affects the formation of crystalline Se making chemical bonds in the crystallographic network stronger.     

On the backscattering factor in quantitative Auger electron spectroscopy of binary alloys

The matrix dependent relative sensitivity factor S_rel(c) is considered for use in quantitative Auger analysis. It is affected by matrix dependent factors like the backscattering factor, the escape depth of Auger electrons and the number of atoms per unit volume. The backscattering factor, especially, is evaluated and possibilities of its determination are shown. Measurements of Auger intensities and of the energy distribution of backscattered electrons were carried out for this purpose on a series of CuPd and CuSb alloys, respectively. The backscattering factor thus obtained is compared with values resulting from a formula of JABLONSKI and by experimental data of SMITH and GALLON .     

CBE growth of GaAs/GaAlAs HBTs using the new DEAlH-NMe3 precursor and all-gaseous dopants

This paper describes the first reported use of diethylaluminium hydride-trimethylamine adduct (DEAlH-NMe₃) for the growth of GaAs/GaAlAs power heterojunction bipolar transistors (HBTs) by chemical beam epitaxy (CBE). This precursor possesses a significantly higher vapour pressure than the more conventionally used triethylaluminium (TEA), and leads to much less stringent requirements for bubbler and gas-line heating, and also much-improved GaAs/GaAlAs heterojunction definition when no carrier gas is employed. The use of all-gaseous n- and p-type dopants offers significant technological advantages in CBE, and the current paper also provides the first report of the use of hydrogen sulphide for n-type doping of CBE-grown GaAlAs HBT emitter regions. In conclusion, DC and RF data obtained from the heterojunction bipolar transistors fabricated to date are described. A DC gain of 40 has already been measured and encouraging early data obtained from RF-probed devices are also presented.     

Short-range atomic order in the surface layer of sputter-deposited Al0.6W0.4 thin film investigated using directional elastic peak electron spectroscopy

A mechanism of creating maxima in directional elastic peak electron spectroscopy (DEPES) polar profiles for textured polycrystalline samples and for amorphous samples with a short-range atomic order is proposed and discussed. DEPES was used in investigating the atomic order in Al and W polycrystalline samples. The maxima found in DEPES polar profiles correspond with the texture expected for these samples on the basis of literature data. A method of processing DEPES data of amorphous metallic alloy with a short-range atomic order is proposed and successfully used for an Al_0.6W_0.4 alloy. The results obtained indicate that nanocrystals with an average linear size in the range of 1 nm and with a particular orientation with respect to the sample surface are present in the surface layer of the sample investigated. A concentration of nanocrystals with such orientation equal to 1.9 × 10¹⁹/cm³ was found when using of the contrast obtained for the maximum in the DEPES polar profile, corresponding to an incidence angle of zero. The contrast of DEPES profiles for the Al_0.6W_0.4 sample increases remarkably during annealing at 373 K. An increase in the amount of preferentially-oriented nanocrystals is suggested as the probable reason for this increase.     

Fictive temperature measurement of alumino-silicate glasses using IR spectroscopy

A simple IR reflection method was used in a previous study to determine the fictive temperature of silica glasses and a soda-lime glass. The IR method is based upon the fact that the silica structural band of a glass takes a unique wavenumber at a particular fictive temperature. When this method was applied to an alumino-silicate glass in this study, however, the IR reflection peak wavenumber of the glass surface was found to be strongly affected by the reaction of the glass with water vapor in the atmosphere. Still, it was possible to measure the fictive temperature of the alumino-silicate glass using IR spectroscopy by taking an IR reflection of the bulk sample after eliminating the surface layer affected by the reaction with water vapor. The IR peak wavenumber of the silica structural band decreased with increasing fictive temperature for the alumino-silicate glass, similar to silica glass.     

An investigation of the atomic bonding present in amorphous chalcogenide materials by electron spectroscopy

The atomic bonding in amorphous switching materials based on tellurium and germanium has been shown to be largely dependent on the germanium atoms. The results of examination by electron spectroscopy show that germanium atoms can possess five different forms of chemical bonding. These are elemental, oxidised, ‘glassy’, and two states associated with the interatomic compound GeTe. The ‘glassy’ and compound forms of germanium have been found in the amorphous materials. Tellurium, however, shows no significant different in bonding from its elemental state in these materials.     

Investigations on the defect depth of electroerosive-cut Te single crystals by reflection electron diffraction (RHEED)

Results of the experimentally determined defect depth due to electroerosive working of Te single crystals as a function of crystal orientation and electric cutting energy by RHEED are given. The abrasion of the disturbed surface layer was made by chemical etch polishing as well as by bombardment with Ar⁺ ions. The defect depths determined from the RHEED patterns depend on the crystal orientation and the applied cutting energy. In case of the lowest cutting energy, it has a value of about 3 μm for the (0001)-orientation and 6 μm for the (101 0)-orientation, the corresponding values for the highest cutting energy are about 8 μm and 20 μm, respectively. It is discussed in how far defect depths determined from the interpretation of RHEED patterns correspond to the “real defect depths” which can be determined by other measuring techniques.     

90° double reflection high-energy electron diffraction experiments on vicinal surfaces of GaAs

Reflection high-energy electron diffraction (RHEED) experiments recording the intensity of the specular beam in two azimuths have been carried out simultaneously. The critical temperature for the transition from 2D nucleation to step-flow growth was simultaneously estimated in the [ 10] and [110] directions by observing the disappearance of RHEED intensity oscillations on GaAs(001) substrates 2° misoriented towards GaAs(111)A. It was found that the oscillations disappear at a lower substrate temperature in the [110] azimuth. The difference in the transition temperatures was 25°C.     

The detection of impurities on metallic surfaces by means of the electron energy loss spectroscopy

The energy analysis of backscattered low-energy monochromatic electrons is used to investigate the appearances on crystal surfaces in the vacuum during thermal treatment. Up to 500 K hydrocarbons can be detected by electronic excitation. In the interval from 600 K to 1100 K the presence of a carbon-contamination layer follows from the excitations of plasmons. The thickness of the layer influences the ratio of the elastically and inelastically backscattered electrons. The material analysis of the clean surfaces due to temperatures above 1200 K is performed by the excitations of the upper inner atomic shells.     

Investigation of defects in low-temperature-grown GaAs using optical transient spectroscopy

Optical transient current spectroscopy (OTCS) has been used to investigate defects in the low-temperature-grown GaAs after postgrowth rapid thermal annealing (RTA). Two samples A and B were grown at 220°C and 360°C on (0 0 1) GaAs substrates, respectively. After growth, samples were subjected to 30 s RTA in the range of 500–800°C. Before annealing, X-ray diffraction measurements show that the concentrations of the excess arsenic for samples A and B are 2.5×10¹⁹ and 1×10¹⁹ cm⁻³, respectively. It is found that there are strong negative decay signals in the optical transient current (OTC) for the annealed sample A. Due to the influence of OTC strong negative decay signals, it is impossible to identify deep levels clearly from OTCS. For a comparison, three deep levels can be identified for sample B before annealing. They are two shallower deep levels and the so-called As_Ga antisite defect. At the annealing temperature of 600°C, there are still three deep levels. However, their structures are different from those in the as-grown sample. OTC strong negative decay signals are also observed for the annealed sample B. It is argued that OTC negative decay signals are related to arsenic clusters.     

Polarity identification of GaN bulk single crystals (0001) surface by Auger electron spectroscopy

An attempt to identify the polarity of (0001) polar surface of GaN bulk single crystals grown by high nitrogen pressure solution method has been made using Auger electron spectroscopy (AES). AES concentration depth profiles of the top layer in (0001) direction starting from both (0001) faces of the sample have been measured. Distinct difference in the Ga concentration at the sample surface of both faces has been observed. The dependence of Ga eoncentration on depth is also different for both faces of the sample.     

Quantitation of sulfate solubility in borosilicate glasses using Raman spectroscopy

Raman spectroscopy is used here as an innovative technique to investigate sulfate content in borosilicate glasses. Using Raman spectroscopy after having heated the material, the evolution of sulfate amounts can be followed as a function of temperature, time and chemical composition of the starting matrix. The accuracy of this technique was verified using electron probe micro analysis (EPMA), on two systems of glasses (SiO₂–B₂O₃–Na₂O (SBNa) and SiO₂–B₂O₃–BaO (SBBa)) in order to compare the effect of alkaline or alkaline-earth elements on sulfur speciation and incorporation. To quantitate sulfate content with Raman spectroscopy, the integrated intensity of the sulfate band at 990 cm^?1 was scaled to the sum of the integrated bands between 850 and 1250 cm^?1, bands that are assigned to Qⁿ silica units. Calibration curves were then determined for different samples. The determination of sulfate contents with Raman spectroscopy analysis is possible with an accuracy of approximately 0.1 wt% depending on the composition of the glass. It mainly allows us to follow sulfate removal during the elaboration process and to establish kinetic curves of sulfate release as a function of the viscosity of the borosilicate glass.     

On the limitation of quantitative measurements using transmission electron microscopy

This work discussed the limitation of (scanning) transmission electron microscopy (TEM/STEM) techniques in quantitative measurements in electron-beam-sensitive silicate glasses and glass ceramics. Electron beam induced damages in the silicate glasses containing Na and the glass ceramics containing fluorite nanocrystals were demonstrated. The damages were mainly caused by preferentially removing Na and decomposing CaF₂ into Ca. All the damage phenomena were observed under electron beam intensities, which were much weaker than the intensities used in the conventional high-resolution electron microscopy (HREM) and microanalysis in STEM. Therefore, although the advanced TEM/STEM techniques are very promising in the precise measurement of local composition at ultra-high spatial resolution in some materials, they may not be applicable to Na-containing silicate glasses and glass ceramics containing fluorite nanocrystals.     

Dielectric function of amorphous silicon films,its oxidation and voids,studied by electron spectroscopy

The energy loss spectra of extremely pure and of oxidized amorphous silicon films were measured with 30 keV electrons in the energy loss range 2–25 eV with a resolution of 0.1 eV. The Si films were prepared by electron beam evaporation at a pressure below 10^?9 Torr during the evaporation process. The influence of contact to the atmosphere and to water on the energy loss spectrum was also investigated. The energy loss spectra can be described well by means of the dielectric theory extended to a multilayer system. The results of the measurements lead to the conclusion that the density of voids in the pure a-Si films deposited at room temperature is less than 5% of the bulk. This should be true as long as the effect of the voids can be described by a dielectric function.     

Well parameters of two‐dimensional electron gas in Al0.88In0.12N/AlN/GaN/AlN heterostructures grown by MOCVD

Resistivity and Hall effect measurements were carried out as a function of magnetic field (0‐1.5 T) and temperature (30‐300 K) for Al_0.88In_0.12N/AlN/GaN/AlN heterostructures grown by Metal Organic Chemical Vapor Deposition (MOCVD). Magnetic field dependent Hall data were analyzed by using the quantitative mobility spectrum analysis (QMSA). A two‐dimensional electron gas (2DEG) channel located at the Al_0.88In_0.12N/GaN interface with an AlN interlayer and a two‐dimensional hole gas (2DHG) channel located at the GaN/AlN interface were determined for Al_0.88In_0.12N/AlN/GaN/AlN heterostructures. The interface parameters, such as quantum well width, the deformation potential constant and correlation length as well as the dominant scattering mechanisms for the Al_0.88In_0.12N/GaN interface with an AlN interlayer were determined from scattering analyses based on the exact 2DEG carrier density and mobility obtained with QMSA. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)