^69,71 Ga and ¹⁴ N high‐field NMR of gallium nitride films

Abstract

Gallium nitride thick films produced by HVPE having varying levels of defects have been characterized by 69,71 Ga and 14 N NMR at high field (11.7 T). The highest quality film yields the sharpest NMR peaks, from which highly accurate NMR parameters, viz. nuclear quadrupole coupling constants (NQCC), isotropic chemical shifts and chemical shift anisotropies, could be derived from studies as a function of film orientation. Poorer quality films (larger X-ray rocking curve widths) exhibit markedly broader 71 Ga satellite transition peaks with a longer T 2 relaxation time, and additional high-frequency shoulders or peaks for the central transitions. The linewidths of the 14 N doublet are also broader in the poorer quality films. The 71Ga spectra of films containing high oxygen levels show a new high-frequency central-transition peak with a very short T 1 . The high-frequency peaks in all cases may be due to Knight shifts arising from conduction electrons.

Nitrogen split interstitial center(N−N)Nin GaN: High frequency EPR and ENDOR study

“…6(d)] we deduce a coupling constant of 1.30 MHz which is within the error limits in good agreement with the value deduced from the angular variation of the quadrupole lines. These values agree also with those previously published for as-grown materials of different origin [38,[40][41][42][43]; see also Table IV.…”

Spatially correlated distributions of local metallic properties in bulk and nanocrystalline GaN

“…In addition to the centerband, a set of spinning sidebands spaced at integer multiples of the spinning rate (12 kHz) reflect the 14 N nuclear quadrupole coupling constant (NQCC) arising from (first order) interactions between the nuclear electric quadrupole moment and the electric field gradients at the nucleus. The NQCC is axially symmetric (asymmetry parameter η=0), with a quadrupole coupling constant C q (=e 2 Qq/h)of 24.14 kHz at 296 K [33].…”

“…The greater intensity on the left side of the sideband spectrum indicates that those regions of GaN:Ge having larger Knight shifts also have significantly altered anisotropic interactions that cause their sideband intensities to increase relative to the centerband. In principle these altered interactions could result from changes in the electric field gradients at the 14 N sites that change the NQCC or from an increase in the 14 N chemical shift anisotropy from its value of zero in an undoped GaN film [33]. Although the latter cause seems less likely, the corresponding increase in intensity of Knight-shifted regions seen for the −1 sideband is somewhat less than that for the +1 sideband, an asymmetric behavior that is not expected for alterations of the NQCC alone.…”

Direct detection of nitrogen-14 in solid-state NMR spectroscopy

“…This allowed the symmetry space groups of the structures to be identified as Pbca for silver nitrate and Pa3 for barium and lead nitrates [27]. In the 14 14 N NMR has also been used to study other ammonium and tetramethylammonium salts [33][34][35][36], various phases of ammonium tetrachlorozincates [37], and gallium nitride films [38].…”