Vacancy-type defects in Mg-implanted GaN probed by a monoenergetic positron beam

Abstract

Positron annihilation is a non-destructive tool for investigating vacancy-type defects in materials. Detectable defects are monovacancies to vacancy clusters, and there is no restriction of sampIe temperature or conductivity. Using this technique, we studied defects introduced by Mg-implantation in GaN. Mg ions of multiple energies (15-180 ke V) were implanted to provide a 200-nm-deep box profile with Mg concentration of 4xl0 19 cm-3 . The major defect species of vacancies introduced by Mg-implantation was a complex between Ga-vacancy (VGa) and nitrogen vacancies (VNs). After annealing above 1000°C, these defects started to agglomerate, and the major defect species became (VGa)2 coupled with VNs. The depth distribution ofvacancy-type defects agreed weil with that of implanted Mg, and no large change in the distribution was observed up to 1300°C annealing.

Low-temperature annealing behavior of defects in Mg-ion-implanted GaN studied using MOS diodes and monoenergetic positron beam

“…Although details on PAS were described previously [37][38][39][40] , a brief explanation of PAS is as follows. Upon the annihilation of a positron, a γ-ray is radiated with an energy of 511 keV.…”

“…In these figures, the mean implantation depth of positrons is also indicated at the top. DF GaN exhibits an S of 0.441 37) . The S parameter increased and decreased upon 300 o C and 500 o C annealing, respectively, independent of the Mg ion dose.…”

“…On the other hand, positron annihilation spectroscopy (PAS) is a powerful method for analyzing vacancy defects in various materials. This method has been applied to Mg-ionimplanted GaN [37][38][39][40] . On the basis of the results of PAS for room-temperature Mg ion implantation, the Ga-N divacancy (VGaVN) was mainly detected for as-implanted samples 38) .…”

Vacancy-Type Defects in GaN for Power Devices Probed by Positron Annihilation

“…Thus, the defects introduced by Mg-implantation [V Ga (V N ) 2 ] are thought to couple with those defects and form more large vacancy-type defects [(V Ga ) 2 (V N ) 7 ] when 1000°C annealing is applied. Before annealing, however, the S value for Mg-doped GaN was close to the defect-free value [19], suggesting that high-concentration Mg doping is possible without introducing vacancy-type defects if a sufficient number of Ga and N atoms are provided during the growth process. Thus, such a treatment is likely to be inevitable to reduce the defect concentration for ion-implanted GaN.…”

“…4, because the Mg concentration [Mg] in the damaged region is of an order of 10 19 cm −3 , vacancy-type defects could introduced by the over-doping of Mg, and these could react with the vacancies introduced by ion-implantation. We studied annealing behaviors of defects in Mg-doped GaN grown by MOVPE [19]. The [Mg] value of this sample was 4×10 19 cm −3 , which close to [Mg] in the subsurface region of the Mg-impalnted sample.…”