Optical detection of electron paramagnetic resonance in electron-irradiated GaN

Introduction and recovery of Ga and N sublattice defects in electron-irradiated GaN

“…[4][5][6] The migration barrier predicted by theoretical calculations for the 3− charge state of the isolated Ga vacancy is 1.9 eV. 28 As the experimental activation energy coincides with this value, we obtain the migration barrier of the isolated Ga vacancy as E M V,Ga = E A1 V,Ga = 1.8± 0.1 eV.…”

“…However, they may be complexed with other irradiation-induced defects or residual impurities and survive thermal treatments up to 800 K. 4,5 The more recent ODEPR results suggest that the isolated negatively charged Ga vacancies could also be stable up to 800 K, 7 while the earlier positron experiments performed after room-temperature 2 MeV electron irradiation indicate that the isolated Ga vacancies ͑produced at a rate of 1 cm −1 ͒ anneal out of GaN samples already at 600 K. 8 The results of the irradiations performed with low-energy ͑0.42 MeV͒ electrons 2 suggest that N vacancy donors are produced at a rate of 0.02 cm −1 and N interstitial acceptors at a lower rate of 0.01 cm −1 .…”

“…The defects introduced in electron irradiation of GaN have been studied earlier with electrical and optical methods, [1][2][3] optical detection of electron paramagnetic resonance ͑ODEPR͒, [4][5][6][7] and positron annihilation spectroscopy 8 as well. However, only in the most recent studies 2,3,7 could the measurements be performed in samples with both low impurity content and low dislocation densities, [9][10][11] allowing more accurate observations of the isolated intrinsic point defects.…”

Thermal stability of isolated and complexed Ga vacancies in GaN bulk crystals

“…Indeed, Chow et al 6 used optical detection of electron paramagnetic resonance ͑ODEPR͒ to observe interstitial Ga atoms after such irradiations. At 300 K the Ga interstitials are trapped by other defects, [6][7][8] perhaps by the oxygen atoms present as impurities in GaN. 6,9 The creation of Ga interstitials should be accompanied by the formation of vacant Ga lattice sites, which have, however, escaped direct experimental observation so far.…”

“…2 indicate that Ga vacancies recover in 30-min isochronal heat treatments at 500-600 K. At this temperature, the electrical experiments of Look et al 5 showed an increase in electron mobility, most likely due to the recovery of irradiation-induced defects acting as carrier scattering centers. The defects associated with trapped Ga interstitials are stable at 500-600 K, and anneal at clearly higher temperatures of 700-900 K according to the ODEPR experiments of Bozdog et al 7 and Linde et al 8 This suggests that Ga vacancies recover by becoming mobile defects at 500-600 K. Assuming that the vacancy takes roughly 10 3 -10 5 jumps with an attempt frequency 10 13 s Ϫ1 in the 30-min annealing time, we can convert the recovery temperature of 600 K to an activation energy of 1.5 ͑2͒ eV. This value can be taken as an estimate of the migration energy of Ga vacancies in GaN.…”