R.W. Michelmann

Infrared absorption study of nitrogen in N-implanted GaAs and epitaxially grown GaAs1−xNx layers

Fourier-transform infrared absorption measurements have been carried out in the two-phonon region of GaAs. Implantation of the nitrogen isotopes 14N and 15N, respectively, into bulk GaAs shows that a local vibrational mode at 471 cm−1 (14N) is due to isolated nitrogen. The band is also found in GaAs1−xNx(0<x<0.03) layers grown by solid-source molecular beam epitaxy. The strength of the band correlates quantitatively with the decrease of the lattice parameter determined by x-ray diffraction for x<0.01 and can be used for the assessment of the nitrogen fraction incorporated substitutionally on anion lattice sites.

Chemical bonding and interface analysis of ultrathin silicon-nitride layers produced by ion implantation and Electron Beam Rapid Thermal Annealing (EB-RTA)

Abstract15N2+ions were implanted into c-Si with an energy of 5 keV/atom and fluences ranging from 5×1016 to 2×1017 atoms/cm2 at RT to form ultrathin silicon-nitride layers (SiNx) with different N/Si ratios depending on the fluences (up to an overstoichiometric N/Si ratio of 1.65). The 15N depth distributions were analysed by the resonant nuclear reaction 15N(p, αγ)12C(Eres=429 keV). The implanted samples were processed by Electron Beam Rapid Thermal Annealing (EB-RTA) at 1150° C for 15 s (ramping up and down 5° C/s). The chemical structure of the 15N implantation into Si was investigated by EXAFS and NEXAFS. Channeling-RBS (4He+, E0=1.5 MeV) measurements were performed to observe the transition region (disordered-Si layer, d-Si) being underneath of the SiNx layer (typical values of layer thicknesses:SiNx 24 nm, d-Si 6 nm).

Boron detection using the nuclear reaction 11B(p, α)2α

Abstract The nuclear reaction 11 B(p, α)2α has been used for the determination of boron impurities in silicon. α-particles with a continuous energy spectrum are produced by the three-body-dynamics of this reaction. Therefore, the differential cross section of this reaction has specifically been defined for materials analysis and measured at the three different laboratory angles θ = 108°, 138°, 158°, for incident proton energies between 150 keV and 800 keV. The formalism for concentration measurements has been developed for a thin boron layer and for a homogeneous boron distribution in the target. The concentration has been compared with results of charged particle activation analysis (CPAA) using the nuclear reaction 10 B(d,n) 11 C.

Excitation functions for the reactions 10B(d, n)11C and 12C(d, n)13N for charged particle activation analysis

Abstract Excitation functions for the reactions 10B(d, n)11C and 12C(d, n)13N have been measured in the energy range from 0.5 to 6.0 MeV in 50 and 100 keV steps, respectively. The absolute cross sections were determined by measuring the annihilation radiation of positron emitting radioisotopes produced in the reaction. The overall accuracy of the cross sections is of the order of 8%.

Nuclear reaction channeling

Abstract Nuclear reaction channeling (NRC) provides a tool for the investigation of concentration and lattice location of impurities in a crystal. In this work NRC is applied to the analysis of light element impurities (B, C, N, O) in semiconductor materials (GaAs, Si). Depending on the nuclear reaction used for the investigation, concentrations below 100 ppma are analysed. The channeling angular scans in different crystalline directions allow to specify the site of the impurities up to a range of the thermal vibration amplitude of the host crystal. These results are deduced from the MABIC simulation code.

Investigation of the electronic energy loss of light ions for materials analysis

Abstract The energy loss, straggling and multiple scattering of light ions in materials was investigated. The interaction of charged particles with crystalline materials was calculated on the basis of Lindhards dielectric response function. The contribution of local and global electronic excitation was taken into account. Simulations and experimental results of other authors in random and low indexed crystal directions are compared with the model calculations.

Analysis of Electrically Active Carbon in Semi-insulating Gallium Arsenide by Infrared Absorption Spectroscopy

Carbon in semi-insulating gallium arsenide (GaAs) crystals has been investigated by Fourier-transform IR absorption spectroscopy, spark source mass spectrometry, and charged particle activation analysis. Procedures for the quantitative evaluation of the 582-cm-1 local mode absorption due to carbon on the arsenic sublattice (CAs) are described. The strength of the mode shows a linear correlation with total carbon content measured by spark source mass spectrometry over the concentration range from 3× 1014 to 2×1016 cm-3. The new calibration factor for the integrated absorption at 77 K is (7.2±0.4)× 1015 cm-1, based on a relative sensitivity coefficient of 3.2±0.1 of the spark source mass spectrometry. Calibration factors for the IR absorption method at room temperature are also given.

Computer simulation of channeling in Si and GaAs crystals

A theoretical model and a Monte Carlo based algorithm were developed to calculate the stopping power of energetic ions in crystals and the energy loss and range of the ions in different low-index and random directions. For model calculations zinc-blende crystals were chosen (Si) because of the availability of the target material in good form for experimental purposes. The crystals were experimentally investigated and the simulations were performed in the main crystal directions and also in a random direction. The calculated stopping powers and energy loss spectra were compared with our experimental results and with those from the literature.

Channeling charged particle activation analysis of light impurities at trace levels in GaAs

Abstract Light element trace concentrations of boron, carbon and oxygen in the range of 10 to 150 ppba were localized in monocrystalline, as-grown GaAs by combining the channeling technique with the sensitivity of charged particle activation analysis (CPAA). The experimental data were evaluated using stopping power and ion flux distributions in the crystal channels that were simulated with the Monte Carlo program MABIC (materials analysis by ion channeling) [1]. Si samples have been used as a reference material. The B and O concentrations of the Si samples are in the range of 100 ppma and 8 to 40 ppma respectively. In GaAs trace concentrations of boron, carbon and oxygen were found to be located preferentially in an interstitial position. In Si boron was localized mainly on substitutional sites for concentrations in the 100 ppma range. Oxygen concentrations of 8 to 40 ppma in Si were determined to be dominantly incorporated on interstitial positions.

Localization and mobility of oxygen in monocrystalline GaAs by channeling-NRA

Abstract 16O was implanted into monocrystalline GaAs. The maximum concentration was determined to be 2.2 × 1019 cm−3 in a depth of 2.4 μm. The samples were tempered at 400 and 500°C for 10, 20, 30 and 40 min. The lattice location of the implanted oxygen was determined in combining the channeling technique with nuclear reaction analysis (CHANRA). Angular scans were performed in the 〈100〉 direction of GaAs using the 16O(d,p0)17O reaction with an incident deuterium energy of 1.85 MeV. For the evaluation of the experimental data stopping power and ion flux distributions in the crystal channels were simulated as a function of the incident angle with the program MABIC (materials analysis by ion channeling) [1]. It was found that the oxygen is occupying interstitial and substitutional sites after implantation. Oxygen is disappearing from the substitutional sites during thermal annealing and an equilibrium of two interstitial sites, in the center of the channel and with an average distance of 0.06 nm from the lattice atoms is established.