The influence of Mg doping on the formation of Ga vacancies and negative ions in GaN bulk crystals

Abstract

Gallium vacancies and negative ions are observed in GaN bulk crystals by applying positron lifetime spectroscopy. The concentration of Ga vacancies decreases with increasing Mg doping, as expected from the behavior of the VGa formation energy as a function of the Fermi level. The concentration of negative ions correlates with that of Mg impurities determined by secondary ion mass spectrometry. We thus attribute the negative ions to MgGa−. The negative charge of Mg suggests that Mg doping converts n-type GaN to semi-insulating mainly due to the electrical compensation of ON+ donors by MgGa− acceptors.

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

“…At 300-500 K, the average positron lifetime in the as-grown sample is constant and provides the lifetime of the positron in the delocalized state in the GaN lattice, B = 161 ps at 300 K, in good agreement with previous experiments in defect-free GaN. 18,19 The increase in the average positron lifetime with decreasing temperature at 80-300 K is a clear indication of the presence of negatively charged vacancies, the positron trapping coefficient of which increases with decreasing temperature. The vacancy concentration of these vacancies is close to the detection limit of the method and thus these vacancies are not observed at room temperature.…”

Introduction and recovery of point defects in electron-irradiated ZnO

“…In addition to the ionization energy of the O vacancy, the binding energy to the Rydberg state of the negative-iontype defect is obtained as E b = 40± 10 meV, similar as observed in GaN. 28 The origin of temperature-dependent behavior of the positron data can be seen from the figure. The trapping rate to the Zn vacancies increases as T −0.5 with decreasing temperature, while the thermal detrapping causes the trapping rate to the negative ions to vanish above 150 K. The trapping rates to the two negative defects coincide at temperatures below 70 K.…”

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

“…1͒. As explained earlier, 11 heavily Mg-doped GaN is free of Ga vacancies trapping positrons, and the lifetime ϭ B ϭ160 ps corresponds to positrons annihilating as delocalized particles in the defect-free GaN lattice. Our result B ϭ160 ps is slightly smaller than that reported previously ͑165 ps͒.…”

“…10 Semi-insulating Mg-doped samples were chosen for the experiment, since these are free of native Ga vacancies as shown earlier. 11 The Mg and O concentrations of the samples were ͓O͔ Ϸ͓Mg͔Ϸ10 20 cm Ϫ3 , according to secondary-ion-mass spectrometry. 11 The samples were irradiated with 2-MeV electrons at 300 K to two fluences of ⌽ϭ3ϫ10 17 and 1 ϫ10 18 cm Ϫ2 .…”

“…11 The Mg and O concentrations of the samples were ͓O͔ Ϸ͓Mg͔Ϸ10 20 cm Ϫ3 , according to secondary-ion-mass spectrometry. 11 The samples were irradiated with 2-MeV electrons at 300 K to two fluences of ⌽ϭ3ϫ10 17 and 1 ϫ10 18 cm Ϫ2 . To study the recovery of irradiation-induced defects and the temperature dependence of the positron lifetime spectrum simultaneously, we annealed the samples at temperatures T ann , and thereafter measured positron lifetimes as a function of measurement temperature T meas from 80 K up to T ann Ϫ50 K. The 30-min annealings were done in situ in the 10 Ϫ3 -mbar vacuum of the positron measurement cryostat.…”