X-ray absorption, glancing-angle reflectivity, and theoretical study of the N K- and GaM2,3-edge spectra in GaN

Abstract

A comprehensive study of the nitrogen K edge and gallium M 2,3 edge in gallium nitride is presented. Results of two different experimental techniques, x-ray absorption by total photocurrent measurements and glancingangle x-ray reflectivity, are presented and compared with each other. First-principles calculations of the ͑polarization averaged͒ dielectric response ⑀ 2 () contributions from the relevant core-level to conduction-band transitions and derived spectral functions are used to interpret the data. These calculations are based on the local density approximation ͑LDA͒ and use a muffin-tin orbital basis for the band structure and matrix elements. The angular dependence of the x-ray reflectivity is studied and shown to be in good agreement with the theoretical predictions based on Fresnel theory and the magnitude of the calculated x-ray optical response functions. The main peaks in the calculated and measured spectra are compared with those in the relevant partial density of conduction-band states. Assignments are made to particular band transitions and corrections to the LDA are discussed. From the analysis of the N K and Ga M 2,3 edges the latter are found to be essentially constant up to ϳ10 eV above the conduction-band minimum. The differences in spectral shape found between the various measurements were shown to be a result of polarization dependence. Since the c axis in all the measurements was normal to the sample surface, p-polarized radiation at glancing angles corresponds to Eʈc while s polarization corresponds to EЌc at all incident angles. Thus, this polarization dependence is a result of the intrinsic anisotropy of the wurtzite structure. Spectra on powders which provide an average of both polarizations as well as separate measurements of reflectivity with s polarization and p polarization were used to arrive at this conclusion.

Structural Investigation of Mixed Nitrided Galloaluminophosphates “AlGaPON” by EELS, XAS, and XPS Spectroscopies

“…The large peak extending from 398 to about 404 eV in AG9N6 reveals a structure that is initially reminiscent of the triplet structure characteristic of h-AlN, already interpreted using LMTO, DOS, and MS calculations (45). One can consider the modi"cations to this picture: the increase in the second peak at 403 eV and the damping of the third peak at 405 eV in relation to the N}K ELNES both in h-GaN, the feature of which is coherent with previous NEXAFS studies (46,47), and in PON, suggesting that h-GaN, h-AlN, and PON local environments may partly co-exist around nitrogen atoms. Otherwise, the broad peak at about 423 eV is assigned to a shape resonance (48); its position follows the Natoli rule and is related to the "rst interatomic distances (49).…”

X‐ray absorption spectroscopy in the analysis of GaN thin films

“…The positions of transitions observed in the N K near-edge spectra were entirely consistent with assignments in the band structure calculations of others, 10 but revealed major differences in coordination and geometry around the nitrogen. Films of up to 150 nm thick displayed a spectrum dominated by the single transition at 402 eV, widely attributed to an sp 2 -type environment 11,12 but in this work was resolved to be molecular nitrogen. Thicker films displayed a layered structure, where the surface region more closely resembled the structure of crystalline GaN.…”

Momentum selectivity and anisotropy effects in the nitrogenK-edge resonant inelastic x-ray scattering from GaN

“…PDOS strong angle dependence of the SXA spectra. 9,15 The theoretical SXE/SXA spectra in Fig.1, corresponding to our experimental geometry, were obtained as a superposition of the N p z and N p xy ones weighted according to the (E//c) 2 to (E⊥c) 2 ratio.…”