GaN polarity determination by photoelectron diffraction

Abstract

A nondestructive approach to determine the wurtzite GaN crystal polarity based on X-ray photoelectron diffraction is proposed. The approach, utilizing the ratio of photoemitted electron currents excited by a standard laboratory X-ray source from the N 1s level in the (101¯0) plane at polar angles of 20° and 25°, is tested on GaN crystals. The photoelectron intensity ratio I20/I25 is larger or smaller than unity for GaN(0001) or GaN(0001¯), respectively. The approach can be used for polarity determination of other binary wurtzite crystals. The atom with the smaller electron scattering cross-section should be used as the emitter.

Non-destructive assessment of the polarity of GaN nanowire ensembles using low-energy electron diffraction and x-ray photoelectron diffraction

“…4, the angular distribution of photoemitted electrons measured in sample S-1 is compared with reference measurements carried out on Ga-and N-polar FS-GaN layers. 27 As discussed in Ref. 27, in the 20 -25 range, the angular distribution of photo-emitted electrons allows us to discriminate between Ga and N polarity in a straightforward manner: whereas the intensity decreases for the Gapolar orientation, it increases for the N-polar orientation.…”

“…In this context, it is worth noting that recent experiments demonstrated a great potential of non-destructive surface sensitive techniques such as low-energy electron diffraction (LEED) and x-ray photoelectron diffraction (XPD) to determine the polarity of GaN layers. [26][27][28] In the case of LEED, the intensity-voltage (I-V) curves depend on crystal orientation. 26 Moreover, state-of-the-art theoretical calculations suggest that LEED could also be used to determine the polarity of nanostructures with well-ordered crystal structure.…”

“…29,30 In the case of XPD, the different angular distribution of photo-emitted electrons for Ga-and N-polar GaN layers is used to assess the polarity in a more straightforward manner. 27 In contrast to resonant x-ray diffraction experiments, 17 these measurements do not require the tunable monochromatic radiation of a synchrotron but can be performed using a standard laboratory x-ray source. Therefore, these non-destructive techniques are of potential significant importance if proven capable to determine, in a routine way, the polarity of GaN NW ensembles on a macroscopic scale.…”

“…The N 1s peak intensities were obtained by integrating the Gaussian fits. 27,28 Polar angle plots were normalized on normal emission intensities. In Fig.…”

GaN quantum dot polarity determination by X-ray photoelectron diffraction

“…Recently, we have developed a relatively simple non-destructive X-ray photoelectron diffraction (XPD) based technique for GaN polarity analysis. Polarity of polar [26] and semipolar [27,28] free-standing GaN crystals was determined using Mg Kα source (photon energy 1253 eV) of a typical X-ray photoelectron spectroscopy (XPS) tool. The method is based on the fact that the spatial distribution of neighboring atoms differs for the two opposite GaN crystal orientations and polar angle dependence of photoelectron intensities exhibits local enhancements in the directions toward their atomic neighbors, which is different for opposite crystal orientations [28].…”