resumo
The interest in Be as an impurity in GaN stems from the challenge to understand why GaN can be doped p type with Mg, while this does not work for Be. While theory has actually predicted an acceptor level for Be that is shallower than Mg, it was also argued that Be is not a suitable acceptor because its amphoteric nature, i.e., its tendency to occupy substitutional Ga as well as interstitial sites, would be considerably more pronounced than for Mg and hence lead to self-compensation. Using the emission channeling technique at the ISOLDE/CERN facility, we determined the lattice location of Be-11 (t(1/2) = 13.8 s) in different doping types of GaN as a function of implantation temperature. We find within an accuracy of 0.08 angstrom that the location of interstitial Be is the one predicted by theory. The room temperature interstitial fraction of 11Be was correlated with the GaN doping type, being highest (up to similar to 80%) in p type and lowest in n-GaN, thus giving direct evidence for the amphoteric character of Be. We find that interstitial 11Be fractions are generally much higher than for Mg, which confirms that indeed self-compensation should be considerably more pronounced for Be. With rising implantation temperature, an increasing conversion of interstitial to substitutional Be is observed, involving at least two clearly identifiable steps at 50-150 degrees C and 350-500 degrees C. This suggests that the migration of interstitial Be may be subject to two different activation energies.
palavras-chave
GROWTH; IMPURITIES; VACANCIES; DEFECTS
categoria
Materials Science; Physics
autores
Wahl, U; Correia, JG; Costa, ARG; Lima, TAL; Moens, J; Kappers, MJ; Silva, MRD; Pereira, LMC; Vantomme, A
Grupos
agradecimentos
The authors acknowledge the support of the ISOLDE Collaboration and technical teams. This work was funded by the Portuguese Foundation for Science and Technology (Fundacao para a Ciencia e a Tecnologia, FCT, CERN/FIS-TEC/0003/2019), the Research Foundation-Flanders (FWO), and the KU Leuven (BOF program). The EU Horizon 2020 Framework supported ISOLDE beam times through Grant Agreement No. 654002 (ENSAR2). T.A.L.L. acknowledges the support by FWO (Projects No. 29681 and No. 52152).