Diffractive triangulation of radiative point sources

We describe a general method to determine the location of a point source of waves relative to a two-dimensional active pixel detector. Based on the inherent structural sensitivity of crystalline sensor materials, characteristic detector diffraction patterns can be used to triangulate the location of a wave emitter. As a practical application of the wide-ranging principle, a digital hybrid pixel detector is used to localize a source of electrons for Kikuchi diffraction pattern measurements in the scanning electron microscope. This provides a method to calibrate Kikuchi diffraction patterns for accurate measurements of microstructural crystal orientations, strains, and phase distributions.Comment: 5 pages, 4 figure

Two beam toy model for dislocation contrast in ECCI

Dislocation contrast in the SEM, as observed though electron channelling contrast imaging (ECCI), is commonly treated analogously to the contrast in the TEM. This perception is based on early studies done for dislocations parallel with the surface where the surface relaxation is negligible. However, for threading dislocations (TD) that interact with the surface (normal or inclined), as is the case for nitrides materials, g b type invisibility criteria are no longer fully applicable to ECCI, especially in forward geometry [1]. Dislocations change locally the lattice curvature and Bragg diffraction conditions in the crystal, affecting the form and diffracting behaviour of the electron wavefunction in that region. More explicitly, Howie and Whelan [2] had shown that dislocation contrast is the result of interband transitions between Bloch waves states which, in turn, are caused by the change in the displacement field, u(r), around the dislocation or local “strain”. Dynamical models have been used successfully to both predict and characterise dislocations in ECCI [3]. Nevertheless, the behaviour of dislocation contrast in ECCI in particular and diffraction contrast in the SEM in general remains somewhat opaque. In the work we investigate the behaviour of contrast causing strain as a means of insight into this problem

Characterization of the blue emission of Tm/Er co-implanted GaN

Comparative studies have been carried out on the cathodoluminescence (CL) and photoluminescence (PL) properties of GaN implanted with Tin and GaN co-implanted with Tin and a low concentration of Er. Room temperature CL spectra were acquired in an electron probe microanalyser to investigate the rare earth emission. The room temperature CL intensity exhibits a strong dependence on the annealing temperature of the implanted samples. The results of CL temperature dependence are reported for blue emission (similar to 477 nm) which is due to intra 4f-shell electron transitions ((1)G(4)-> H-3(6)) associated with Tm3+ ions. The 477 nm blue CL emission is enhanced strongly as the annealing temperature increases up to 1200 degrees C. Blue PL emission has also been observed from the sample annealed at 1200 degrees C. To our knowledge, this is the first observation of blue PL emission from Tin implanted GaN samples. Intra-4f transitions from the D-1(2) level (similar to 465 nm emission lines) of Tm3+ ions in GaN have been observed in GaN:Tm films at temperatures between 20-200 K. We will discuss the temperature dependent Tm3+ emission in both GaN:Tm,Er and GaN:Tm samples

Microscopy of defects in semiconductors

In this chapter, the authors discuss microscopy techniques that can be useful in addressing defects in semiconductors. They focus on three main families: scanning probe microscopy, scanning electron microscopy and transmission electron microscopy. They first address the basic principles of the selected microscopy techniques In discussions of image formation, they elucidate the mechanisms by which defects are typically imaged in each technique. Then, in the latter part of the chapter, they describe some key examples of the application of microscopy to semiconductor materials, addressing both point and extended defects and both two-dimensional (2D) and three-dimensional (3D) materials

Dynamical simulations of transmission Kikuchi diffraction (TKD) patterns

Truly nanostructured materials pose a significant spatial resolution challenge to the conventional Electron Backscatter Diffraction (EBSD) characterization technique. Nevertheless, the interaction volume can be reduced by the use of electron transparent samples and the acquisition of electron backscatterlike patterns (EBSP) in transmission mode instead. These transmission Kikuchi diffraction (TKD) patterns are typically acquired by mounting a thin foil, similar to transmission electron microscopy (TEM), and tilting it at a slight angle (20◦ -30◦ ) from horizontal towards a standard EBSD camera

Spatial clustering of defect luminescence centers in Si-doped low resistivity Al0.82Ga0.18N

A series of Si-doped AlN-rich AlGaN layers with low resistivities was characterized by a combination of nanoscale imaging techniques. Utilizing the capability of scanning electron microscopy to reliably investigate the same sample area with different techniques, it was possible to determine the effect of doping concentration, defect distribution, and morphology on the luminescence properties of these layers. Cathodoluminescence shows that the dominant defect luminescence depends on the Si-doping concentration. For lower doped samples, the most intense peak was centered between 3.36 eV and 3.39 eV, while an additional, stronger peak appears at 3 eV for the highest doped sample. These peaks were attributed to the (VIII-ON)2− complex and the V3−III vacancy, respectively. Multimode imaging using cathodoluminescence, secondary electrons, electron channeling contrast, and atomic force microscopy demonstrates that the luminescence intensity of these peaks is not homogeneously distributed but shows a strong dependence on the topography and on the distribution of screw dislocations.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, BauelementeBMBF, 13N12587, Photonische Plattformtechnologie zur ultrasensitiven und hochspezifischen biochemischen Sensorik auf Basis neuartiger UV-LEDs (UltraSens

Energy-weighted dynamical scattering simulations of electron diffraction modalites in the scanning electron microscope

Transmission Kikuchi diffraction (TKD) has been gaining momentum as a high resolution alternative to electron back-scattered diffraction (EBSD), adding to the existing electron diffraction modalities in the scanning electron microscope (SEM). The image simulation of any of these measurement techniques requires an energy dependent diffraction model for which, in turn, knowledge of electron energies and diffraction distances distributions is required. We identify the sample-detector geometry and the effect of inelastic events on the diffracting electron beam as the important factors to be considered when predicting these distributions. However, tractable models taking into account inelastic scattering explicitly are lacking. In this study, we expand the Monte Carlo (MC) energy-weighting dynamical simulations models used for EBSD [1] and ECP [2] to the TKD case. We show that the foil thickness in TKD can be used as a means of energy filtering and compare band sharpness in the different modalities. The current model is shown to correctly predict TKD patterns and, through the dictionary indexing approach, to produce higher quality indexed TKD maps than conventional Hough transform approach, especially close to grain boundaries

You do what in your microprobe?! The EPMA as a multimode platform for nitride semiconductor characterization

While the use of electron probe microanalysis (EPMA) is widespread in the geological and metallurgical sciences, it remains less prevalent in the field of semiconductor research. For these materials, trace element (i.e. dopant) levels typically lie near or beneath the detection limit of wavelength-dispersive Xray (WDX) spectrometers, while alloy compositions of ternary mixtures and multilayer structures can more readily be determined using X-ray diffraction techniques. The electron beam measurements more commonly applied to semiconductors remain transmission electron microscopy (for structural characterization), and scanning electron microscopy (topographic, optical and electrical information). Despite this, there are many aspects of the EPMA that make it an attractive platform for all of thesetypes of semiconductor characterization, particularly when combining compositional information fromWDX with complementary and simultaneously-acquired signals. These advantages include: built-inlight optics; a stable, quantified and high-current beam; and a combined large-area and high-resolutionmapping capability. This allows the measurement of cathodoluminescence (CL), electron beam-inducedcurrent (EBIC) and electron channelling contrast imaging (ECCI) signals alongside WDX, which weapply to the investigation of visible and UV AlxInyGa1-x-yN materials, devices and nanostructures

Report on the evening rump session on InN - July 21, 2004 at the 2004 international workshop on nitride semiconductors

The following is a report on the Evening Rump Session on InN held as part of the 2004 International Workshop on Nitride Semiconductors. It summarises (1) the presentations given by the 5 panellists covering data generated from theory and a wide range of experimental techniques relating to the properties of InN, in particular its bandgap and (2) the subsequent discussion. The most recent parameter-free electronic-structure calculations predict a value for the InN bandgap of 0.8 +/- 0.4 eV; experimental results obtained from a wide range of InN samples point to a bandgap around 0.7 eV, or to a bandgap around 1.3 eV. The interpretation of available data is hotly contested, not surprisingly a definitive conclusion on the true value of the bandgap of InN was not reached during the Rump Session. It was agreed that InN is a difficult material to grow and its properties vary depending on how and where it is grown. However with mobilities of order 4000 cm(2)/Vs, high saturation velocities and the absorption wavelengths of InGaN spanning the visible, InN is a material with huge potential