Incorporation of the transition metal Hf into GaN

The perturbed angular correlation (PAC) technique was applied to study the incorporation of the transition metal Hf into GaN after implantation. To this end the PAC probe 181Hf(181Ta) was implanted into epitaxial Wurtzite GaN layers (1.3 μm on sapphire) with an energy of 160 keV and doses of 7x 1012 at/cm2. PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in the 300-1000 deg. C temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency (QIF) of νQ= 340 MHz for 30% of the probe nuclei. Annealing up to 600 deg. C reduces the damping of this frequency without an increase of the probe atom fraction fs in these sites. Above 600 deg. C fs grows rapidly until after the 900 deg. C RTA step more than 80% of the Hf probes experience a well defined QIF due to the incorporation of Hf on undisturbed sites of the hexagonal GaN wurtzite lattice. An interaction frequency of νQ= 340 MHz is derived. RTA and furnace annealing yield similar results for annealing up to 800 deg. C, where the undisturbed fraction reaches about 60%. Then RTA at higher temperatures increases this fraction, while furnace annealing leads to a decrease down to 22% after annealing at 1000 deg. C. To our knowledge this is the first time that a transition metal probe like Hf is incorporated to such a large extent into a semiconductor lattice