Donor impurity excitation spectra in the infrared from two high-quality, not-intentionally doped, hydride-vapor-phase epitaxial GaN wafers are reported. Two previously observed shallow donors which we designate N1 and N2 were observed in both wafers. However, spectra of one wafer are dominated by N1 and spectra of the other by N2. A comparison of infrared and secondary ion mass spectroscopic data allows identification of N1 as Si and N2 as O. Silicon is the shallowest uncompensated donor in these samples with an activation energy of 30.18±0.1 meV in the freestanding Samsung wafer. The activation energy of O is found to be 33.20±0.1 meV. An unidentified third donor with an activation energy of 31.23±0.1 meV also was observed. Integrated absorption cross sections are found to be 8.5×10−14 cm for Si and 8.6×10−14 cm for O.

High-resolution, variable-temperature photoluminescence studies of recombination processes associated with excitons bound to donors in hydride-vapor-phase epitaxial GaN are presented. Detailed analyses of the two-electron satellite ͑2ES͒ region identify transitions associated with ground and excited states of both the donor-bound exciton complexes and of the donor itself. All of the 2ES transitions observed in this work can be accounted for by the recombination of excitons bound to Si and O substitutional impurities and the line positions are in excellent agreement with the energies of donor intraimpurity transitions measured previously by infrared absorption. Conflicting aspects of donor identification and the binding energies of impurities and excitons are clarified.

Electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR) experiments have been performed on a set of GaN epitaxial layers doped with Mg from 2.5 x 10(18) to 5.0 x 10(19) cm(-3). The samples were also characterized by secondary-ion-mass spectroscopy (SIMS), temperature-dependent Hall effect, and low-temperature photoluminescence (PL) measurements. EPR at 9 QHz on the conductive films reveals a single line with g(parallel to)similar to2.1 and g(perpendicular to)similar to2 and is assigned to shallow Mg acceptors based on, The similarity of the spin density with that found for the number of uncompensated Mg shallow acceptors from Hall effect and the total Mg concentration by SIMS. PL bands of different character are observed from these layers,, including shallow-donor-shallow-acceptor recombination at 3.27 eV from the lowest,doped sample, and, in most cases, broad emission bands with peak energy between 2.9 and 3.2 eV from the more heavily doped films. In addition, several of the films exhibit a weal, broad emission band between 1.4 and 1.9 eV. ODMR at 24 GHz on the "blue" PL bands reveals two dominant features. The first is characterized by g(parallel to),g(perpendicular to)similar to1.95-1.96 and is assigned to. shallow effective-mass donors. The second line is described by similar g tensors as found by the EPR experiments and, thus, is also attributed to shallow Mg acceptors. Although several groups have related the 2.8 eV PL in heavily Mg-doped GaN with the formation of deep donors, no clear evidence was found from the ODMR on this emission for such centers. However, based on the near-midgap PL energy and the observation of the feature assigned to shallow Mg acceptors, the strongest case from magnetic resonance for the existence of deep donors in these films is the isotropic ODMR signal with g = 2.003 found on emission, <19 eV. Possible recombination mechanisms to account for-the ODMR on these "blue" and near-IR PL bands are discussed

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Self-nucleated bulk AlN crystals were grown by thermodecomposition of AlCl3⋅NH3 vaporized in the low-temperature zone of a two-zone furnace. X-ray diffraction of the AlN crystals show single lines with a small linewidth indicating high single-crystalline quality. Polarized Raman scattering experiments of these samples confirm the x-ray results based on the detection of a small linewidth for all allowed optical phonons. Low-temperature cathodoluminescence spectra show very sharp emission bands close to the optical band gap, which have been assigned to free-excitons A and B, and exciton-bound to shallow neutral impurity. The latter has a full width at half maximum smaller than 1.0 meV.

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PACS 71.55.Eq, 78.30.Fs, 78.55Cr, 78.66.Fd High-resolution, variable temperature PL experiments were performed in the spectral region associated with recombination processes involving the ground and excited states of the neutral donor bound excitons. High-resolution infrared measurements in combination with high-sensitive SIMS unambiguously identified Si and O shallow donors and yield their ground state binding energies. These binding energies are in excellent agreement with values obtained by the analysis of the two-electron-satellite PL spectra considering the participation of ground and excited state donor bound excitons. This work clarifies conflicting aspects existing in donor identification and the binding energies of the impurities and excitons.