Use of dynamical diffraction effects on x-ray fluorescence to determine the polarity of GaP single crystals

Abstract

The dynamical theory of x-ray diffraction, which predicts a highly structured internal field intensity during symmetric Bragg reflection from large single crystals, was applied to the~(111)and~(222) Bragg reflections from noncentrosymmetric GaP crystals. It was shown that theory predicts an internal field intensity with maximal and minimal surfaces. At the low-angle side of the region of total reflection, the surface of maximal field intensity is positioned to sense the least amount of charge density. The field intensity moves into the crystal during the scan of the total reflection range until it senses the maximum amount of charge density at the high-angle limit of total reflection. During scans of the (111)and (TTT) reflections, the field intensity moves across the atomic planes in different sequences so that the polarity of the crystal may be determined by monitoring the x-ray fluorescence from the phosphorus or gallium atoms. This polarity determination does not reguire an anomalously scattered component in the difFracted beam as have all previous determinations.Experimental phosphorus fluorescence profiles were obtained during diffraction of Cu Ka radiation from thẽ (111)and~ (222) reflections. The long-wavelength phosphorus Ka radiation provided distinct advantages in detecting the internal field motion, and the~(222) reflection profiles provided internal checks on the~ (111) results. The experimental profiles agreed with theoretical predictions and determined the Gap crystal polarity.The polarity was also determined by the traditional anomalous dispersion method using Mo Ka radiation.The two methods gave consistent results providing experimental confirmation of the predictions of dynamical and kinematic theories of x-ray difFraction. The fluorescence technique also provides a means for determining the arrangement of atoms in crystals in a new and direct way.

Two-dimensional electron gases induced by spontaneous and piezoelectric polarization charges in N- and Ga-face AlGaN/GaN heterostructures

“…36 The method is based on generating an XSW field by x-ray Bragg diffraction and monitoring the x-ray fluorescence yield excited by this field as a function of glancing angle as the GaN layer is turned through the narrow region of Bragg reflection. Determining the polarity of noncentrosymmetric crystals with the XSW technique is straight forward and has been demonstrated for GaP 37,38 and GaAs. 39,40 In the case of a wurtzite GaN film with a thickness of 1 m grown by PIMBE ͑similar to the first layer of structures B and C͒ without nucleation layer, the XSW technique was successfully applied.…”

Theory and applications of x-ray standing waves in real crystals

“…It leads to a weak variation in the slope of the linear part, i.e., to a weak decline in the intensity yield at this angles. It is interesting to note here, that this actual form of the standing wave curve contain information about the real escape depth of the secondary radiation, that can be obtained by fitting experimental data to theoretical calculations in the form of equation (59). This effects were observed experimentally in the case of the fluorescence radiation [54] (change of the depth of yield L yi was obtained by the change of the exit angle of the fluorescence yield) and in the case of photoeffect [55] (see Fig.…”

Directional fine structure in absorption of white x rays: A tomographic interpretation

“…Notably, one of the first experiments demonstrating the capabilities of XSW was performed for this crystal. 24 Secondly, highquality GaP wafers are commercially available in both orientations along the ͓111͔ direction. This allows investigation of the extinction effects that can arise in holographic methods.…”