Martin Herms

Size analysis of nanocrystals in semiconductor doped silicate glasses with anomalous small-angle x ray and Raman scattering

Semiconductor doped glasses containing CdSxSe1−x nanocrystallites embedded in a silicate glass matrix were investigated. The dimensions of the nanocrystallites are in the range of a few nanometers and vary as a function of a secondary heat treatment. The confinement of such quantum dots for elementary excitations depends strongly on their size. In order to obtain a mean particle size and the size distribution, anomalous small angle x-ray scattering (ASAXS) and low-frequency inelastic Raman scattering measurements were performed. The sizes and the size distributions were evaluated for samples of different mean crystallite radius and composition x. The results of Raman measurements agree well with those of ASAXS, if both the acoustic mode damping across the nanocrystallite–matrix interface and the particle size distribution are taken into account in the Raman band shape analysis. The concentration of nanocrystallites in the glass matrix was determined by using the technique of contrast variation. Scattering...

Determination of the charge carrier concentration across growth striations in n‐GaAs by Raman spectroscopy

Using a Raman microprobe, the charge carrier concentration across growth striations in Bridgman n‐GaAs is determined both by the analysis of coupled LO‐phonon‐plasmon modes and their relative intensities compared to that of the uncoupled LO phonon of the depletion layer. It is shown that the charge carrier concentration typically varies by ±10% in the regions both under rough and facetting growth conditions. In the facetting grown region the charge carrier concentration appears to be higher by about 50%.

Raman probe of new laser materials GaAs 1-x Bi x and InAs 1-x Bi x

Inclusion of a small amount of Bi in InAs and GaAs changes the temperature dependent behavior of the band gap. Both InAs1- xBix and GaAs1-xBix tend to have temperature insensitive band gap with increasing Bi content. Raman scattering has been performed on the epilayers of InAs1- xBix and GaAs1-xBix compounds grown by MOVPE technique for varying Bi content. Good single crystalline growth with spatial homogeneity was confirmed using micro- Raman technique. Vibrational modes of InBi and GaBi were observed in the two materials, respectively. In addition, vibrational modes corresponding to Bi and phonon-plasmon coupled modes were also observed. Experimental results indicate that Bi atoms homogeneously replace some of the As atoms in both InAs as well as in GaAs to provide good crystalline structures of InAs1-xBix and GaAs1- xBix compounds, respectively.

Copper Through Silicon Vias Studied by Photo-elastic Scanning Infrared Microscopy

Abstract The in-plane stress distribution in copper through silicon vias (TSV) ensembles of different design has been studied by the scanning infrared stress explorer (SIREX). SIREX is a reflection-based plane polarimeter particularly developed for the high-resolution stress state visualization in silicon-based electronic and mechanic devices. The SIREX method is based on the principle of stress-induced birefringence. We demonstrate that the silicon crystal matrix around the TSV is optically anisotropic with a stress distribution being similar to fields which are known from point-like stress sources. The maps of optical anisotropy have been converted into maps of difference of principal stress components Δσ with a resolution of a few kPa. We show that magnitude and direction of Δσ depend on the geometrical design of the TSV, in particular on length and diameter. The average radial profile of magnitude is discussed. In consequence, we offer a promising tool and method for the non-destructive evaluation of TSV structures in view of their stress characteristics and integrity.

Comparative Spatially Resolved Characterization of a Czochralski-Grown Silicon Crystal by Different Laser-Based Imaging Techniques

The axial distribution of electrical and optical properties of a 4 inch Czochralski-grown silicon single crystal were analyzed by different methods that can be applied in the scanning mode. These methods were tested with respect to the suitability to reveal growth striations. The residual stress was visualized by SIRIS (Scanning Infrared Stress Inspection System) and SIREX (Scanning Infrared Stress Explorer), the electrical resistivity by LPS (Lateral Photovoltage Scanning) and SRP (Spreading Resistance Profiling), and the lifetime of the minority charge carriers by MDP (Microwave Detected Photoconductivity) mapping. The concentration of interstitial oxygen (Oi) across the growth striations was determined by FTIR (Fourier Transform Infrared) spectroscopy. We demonstrate for the first time on the micrometer scale that the Oi scan is very well-correlated with the profile of Δσ (difference of the in-plane principal stress components). The stress field is tensile oriented in growth direction, i. e. perpendicularly to the growth striations. The stress-concentration coefficient has been estimated to be in the order of 10-13 Pa cm-3 what does agree well with previous XRD results.