Positron study of ion-cutting process in GaN

We report on the nature of vacancy complexes and voids involved in H ion-induced splitting of free standing fs-GaN. The fs-GaN wafers were subjected to room temperature implantation with 50 keV H ions at a fluence of 2x10¹⁷ H cm^-2. After implantation, the wafers were annealed at different temperatures ranging from 100 to 600 °C. Variable energy Doppler broadening spectroscopy (VEDBS) was used in order to probe open-volume defects and their thermoevolution. Pulsed low energy positron lifetime spectroscopy (PLEPLS) was employed to qualitively characterize H ion-induced vacancy complexes and to observe their subtle changes during the thermally activated splitting of GaN thin layer. The decomposition of the lifetime spectra of as-implanted and annealed samples up to a temperature of 450 °C resulted in the detection of two vacancy defects: divacancies (260-282 ps) and vacancy clusters (470-650 ps). With increasing temperature, we have noted in addition the existence of other kind of vacancy-type defects, namely, monovacancies (220-236 ps) and a long lifetime which is attributed to positronium. From the values of positronium lifetime equal to 1 ns, 2.2 ns and 3.8 ns, it was possible to estimate the corresponding wall spacing according to the Tao-Eldrup model to be 0.2 nm to 0.4 nm. The fact that positron annihilation spectroscopy can give information about the wall spacing in GaN, leads us to say that this technique is able to predict the phenomenon of splitting in wide band gap semiconductors.