(a) Schematic representation of the charge transfer level of Fe in GaN. Since level is transferred from to by capturing a free electron, an Fe atom acts as a compensating deep acceptor in GaN. (b) Schematic representation of the energy level diagram of in GaN:Fe. The emission mechanisms of spin-forbidden internal transition are shown by the arrows labeled (i)–(iii).
Fe concentration [Fe] (open circles) and resistivity (closed squares) as a function of partial pressure of HCl flown on the Fe metal. The value of higher than was obtained when [Fe] was higher than the major shallow donor (Si) concentration . A schematic representation of the sample structure is also shown.
PL spectra of undoped FIELO-GaN and GaN:Fe films measured at (a) 8 K and (b) 300 K. (c) The NBE PL spectrum of undoped FIELO-GaN at 8 K.
(a) IR PL spectra of the GaN:Fe film at 13 and 300 K. A sharp zero-phonon line at 1.300 eV and its phonon replicas were observed (see also Table I). The PL spectrum at 13 K in the vicinity of the zero-phonon line is magnified in (b). The so-called hot lines (Ref. 38) in the higher energy side have been attributed to be due to the splitting of the excited state of [see Eq. (3) in text] under the combined effects of spin-orbit coupling, Jahn–Teller coupling (Ref. 39), and the symmetry change from to in inhomogeneously distorted sites.
Doppler broadening parameter of undoped FIELO-GaN (open circles) and GaN:Fe (closed squares) films as a function of incident positron energy . The mean implantation depth of positrons is given in the upper horizontal axis.
for the annihilation of positrons trapped by vacancy-type defects in undoped and Fe-doped GaN measured by the CDB detection system (closed symbols). The values shown by the open symbols were obtained through the first principles calculations for the positron annihilation in defect-free (bulk) , , divacancy, and quadravacancy (see Ref. 41).
Values of (a) , (b) , (c) , and (d) in the bulk region, and (e) positron diffusion length before and after annealing in , as a function of annealing temperature. The bulk values of , , , and of undoped FIELO-GaN are also shown at the left edge.
PL spectra at (a) 8 K and (b) 300 K of the GaN:Fe film before and after annealing in ambient between 600 and .
(a) relations for the GaN:Fe film annealed in at (closed circles), (open triangles), and (crosses). Characteristic parameters for the undoped and as-grown GaN:Fe films are indicated by the arrows on the right vertical axis. (b) Depth distribution of obtained by the fitting for the sample annealed at .
relationships for the annihilation of positrons in GaN. The plots for (, ) are the present results for undoped FIELO-GaN (closed triangle), as-grown GaN:Fe (closed plots), and annealed GaN:Fe (open circles with the annealing temperature as the sample identification). For comparison, values of a variety of GaN samples measured previously are plotted for >0.44 without straight lines. They are unintentionally doped GaN samples exhibiting negligible YL band (open symbols) and strong YL band (closed symbols). Those samples were grown either by MOVPE, MBE, or HVPE, and had -, -, or -plane surface. TDDs of the samples were varied from to . The samples exhibiting strong YL band contained high concentration oxygen, which was measured by SIMS. The sample details are given in Refs. 23 and 54. values obtained through the first principles calculations for the positron annihilation in defect-free (bulk) , , divacancy, and quadravacancy (Ref. 41) are also plotted by the open symbols, which are connected by the straight lines.
IR PL peak energies at 13 K of the GaN:Fe film . Energy differences relative to zero-phonon line at 1.300 eV are shown in the third column.
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