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 th is end the PAC probe Hf-181(Ta-181) was implanted into epitaxial Wurtzite G aN layers (1.3 mu m on sapphire) with an energy of 160 keV and doses of 7 X 10(12) at/cm(2). PAC spectra were recorded during an isochronal annealing programme, using rapid thermal annealing (RTA) and furnace annealing, in th e 300-1000 degrees C temperature range. After implantation the spectra show a damped oscillation corresponding to a quadrupole interaction frequency ( QIF) of nu(Q) = 340 MHz for 30% of the probe nuclei. Annealing up to 600 de grees C reduces the damping of this frequency without an increase of the pr obe atom fraction f(S) in these sites. Above 600 degrees C f(S) grows rapid ly until after the 900 degrees C RTA step more than 80% of the Hf probes ex perience a well defined QIF due to the incorporation of Hf on undisturbed s ites of the hexagonal GaN wurtzite lattice. An interaction frequency of nu( Q) = 340 MHz is derived. RTA and furnace annealing yield similar results fo r annealing up to 800 degrees C, where the undisturbed fraction reaches abo ut 60%. Then RTA at higher temperatures increases this fraction, while furn ace annealing leads to a decrease down to 22% after annealing at 1000 degre es 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 lattic e.