Magnetic resonance studies of Mg-doped GaN epitaxial layers grown by organometallic chemical vapor deposition

Abstract

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

Origin of the red luminescence in Mg-doped GaN

“…At the high field side of the sharp signal two other, overlapping, luminescence-enhancing resonances are observed, which are better resolved in measurements performed at 34 GHz [10]. From comparison with previous magnetic resonance work [3,11,12,13], the narrower resonance, with g = 1.952 ± 0.003 and FWHM = 8 -10 mT, is attributed to effective-mass (EM) donors. The g-value of the broader signal (g = 1.967 ± 0.005) is close to that of a deeper donor signal (g = 1.962) detected from the 2.75 -3.1 eV spectral region of both the as-grown and annealed samples that we have studied here [10], suggesting that the same deeper donor is associated with both the 2.8 eV "blue" band and the 1.8 eV "red" band.…”

“…The g-value of the broader signal (g = 1.967 ± 0.005) is close to that of a deeper donor signal (g = 1.962) detected from the 2.75 -3.1 eV spectral region of both the as-grown and annealed samples that we have studied here [10], suggesting that the same deeper donor is associated with both the 2.8 eV "blue" band and the 1.8 eV "red" band. In addition to the PL-enhancing lines, an asymmetric quenching signal with a g-value of about 2.105 is detected, and is attributed to shallow Mg acceptors [11]: its PL-quenching character indicates that it is a center involved in a recombination process competing with the red emission. The ODMR results presented above suggest that donor (EM and/or deeper)-to-deep-center recombination is responsible for the red emission.…”

Formation and dissociation of hydrogen-related defect centers in Mg-doped GaN

“…The origin of this band is still not completely understood and recent experimental results indicate that it might consist of more than one emission band [5,22]. Most researchers agree that the blue band is caused by a transition between a deep localized donor and an acceptor state (likely a Mg-related acceptor) [4,5,23]. Both theoretical [4,24] and experimental [4,5] studies concluded that the incorporation of high Mg concentrations is accompanied by a formation of additional deep donors.…”

“…However, there is a limited number of possible candidates both for the shallow acceptor and the shallow donor(s) involved in the DAP. For the shallow acceptor with an optical binding energy of around 225 meV, Mg Ga [8,9] is the most promising candidate. Whereas possible candidates for the shallow donor (20-30 meV) are O [10], Si [11], H [12] and V N -H [13].…”

Characterization of nitrides by electron paramagnetic resonance (EPR) and optically detected magnetic resonance (ODMR)

“…Most notably, no clear evidence is found for deep donors within a simple model that the two features (Mg and EM) observed from ODMR on the broad 2.8 Á/3.2 eV PL bands are associated with the recombining centers. However, we suggest that evidence for the existence of deep donors in several of these samples is found from ODMR on the PL B1.9 eV [48]. In addition to the same Mg-related ODMR feature as observed on the 'blue' PL bands, an isotropic line with g 0 2.00390.002 and FWHM Â 15Á/ 20 mT is also found on this near-IR PL (though the gvalues are very similar, this resonance is much broader than the MM1 signal observed on emission less than 1.9 eV from Mg-doped GaN reported in [18]).…”