Cathodoluminescence Study on Thermal Recovery Process of Mg‐Ion Implanted N‐Polar GaN

Abstract

Thermal recovery of N‐polar GaN(000true1¯) samples implanted with magnesium and hydrogen ions was investigated by cathodoluminescence (CL) spectroscopy. The high thermal stability of N‐polar GaN allowed annealing process over 1200 °C without protective overlayer. The CL emissions from acceptor‐bound excitons and donor‐bound excitons were observed in the near‐band‐edge (NBE) after annealing over 1000 °C of the ion implanted samples, which indicates the formation of Mg acceptors. The emission intensities both in the NBE and in the green luminescence (GL) band increased with the annealing temperature, resulting from reducing the non‐radiative recombination centers. On the other hand, the enhancement of the GL band (nitrogen vacancy complexes) by prolonging the annealing duration above 1200 °C was not significant as compared to the band‐edge emission, probably resulting from the enhancement of activating the implanted Mg ions. These results give clear directions to improve the quality of Mg‐ion implanted GaN.

Redistribution of Mg and H atoms in Mg-implanted GaN through ultra-high-pressure annealing

“…In the case of UHPA at 1573 K, H-atoms were gradually introduced as the annealing duration increased, indicating gradual substitution of Ga sites by Mg atoms, that is, Mg activation. This result is consistent with the enhancement of Mg activation, estimated by cathodoluminescence measurements, by prolonged annealing, even at temperatures below 1573 K reported by Kataoka et al 24) In the case of UHPA at 1673 K, the increase in the [H] to [Mg] ratio, with increasing annealing duration, is much quicker. It reached 54% for the sample annealed at 1673 K even for less than 1 min duration and 75% for a 5 min duration.…”

Enhanced activation of Mg ion-implanted GaN at decreasing annealing temperature by prolonging duration

“…9) However, the critical issue in Mg ion implantation for p-type doping of GaN has been the poor activation ratio of Mg acceptors compared with that of Mg atoms doped in epitaxially grown p-type GaN. 7,[10][11][12] Since ion implantation inevitably creates point defects, i.e. interstitials and vacancies, and their complexes, 13) the crystallographic defects produced by Mg ion implantation should be responsible for the low activation ratio.…”

“…27) The peaks have complicated structures, and it is difficult to separate the peak intensities from the DAP band at present. Broad green luminescence (GL) around 2.4 eV is commonly observed in Mg ion-implanted GaN and has been assigned to a transition involving V N s. 8,10,28,29) V N reportedly acts as a compensating center in p-type GaN. 19) The luminescence intensity of Mg ion-implanted GaN decreases due to nonradiative recombination centers (NRCs), 30) which likely compensate holes in p-type GaN.…”

Nitrogen-displacement-related recombination centers generated by electron beam irradiation in n-type and p-type homoepitaxial GaN layers

“…Various techniques have been employed to evaluate the properties of point defects in GaN, including deep level transient spectroscopy (DLTS), [10][11][12] positron annihilation spectroscopy, 13,14) photoluminescence, 15) cathodoluminescence 16,17) and carrier lifetime measurements. [18][19][20] Among these, carrier lifetime measurements are best suited to assessing point defects acting as recombination centers (RCs).…”