Physical Review B, 68(20), 205209 (2003)

Calculated properties of nitrogen-vacancy complexes in beryllium- and magnesium-doped GaN

C. D. Latham (a), R. Jones (a), S. Öberg (b), R. M. Nieminen (c), P. R. Briddon (d)

(a) School of Physics, University of Exeter, Exeter, EX4 4QL, United Kingdom

(b) Department of Mathematics, University of Luleå, Luleå, SE-97187, Sweden

(c) Laboratory of Physics, Helsinki University of Technology, P.O. Box 1100, FIN-02015 HUT, Finland

(d) Physics Centre, School of Natural Science, University of Newcastle upon Tyne, Newcastle NE1 7RU, United Kindom

(Received 1 April 2003; revised 1 July 2003; published 20 November 2003)

Abstract

The properties of defect complexes consisting of a nitrogen vacancy with a substitutional beryllium or magnesium atom on neighboring lattice sites in hexagonal GaN are calculated using the AIMPRO local-density-functional theory method.  Both types of defects V_N-Be_Ga and V_N-Mg_Ga are bound with respect to their isolated constituents.  They do not appear to have any electronic levels in the bandgap, and are expected to be neutral defects.  Important structural differences are found.  In its minimum energy configuration, the Be atom in the V_N-Be_Ga complex lies nearly in the same plane as the three equivalent N atoms nearest to it.  Thus, it has shorter Be-N bonds than the Ga-N distance in the bulk crystal, while the Mg atom in the V_N-Mg_Ga complex occupies a position closer the lattice site of the Ga atom it replaces.  Hence, the V_N-Be_Ga complex has a larger open volume than the V_N-Mg_Ga complex.  This is consistent with positron annihilation experiments [Saarinen et al., J. Cryst. Growth 246, 281 (2002); Hautakangas et al., Phys. Rev. Lett. 90, 137402 (2003)].  The frequency of the highest local vibrational mode of the V_N-Be_Ga center is calculated to be within 3-4 % of an infrared absorption line detected in Be-doped GaN [Clerjaud (private communication)].

DOI: 10.1103/PhysRevB.68.205209

PACS: 61.72.Bb, 61.72.Ji, 61.72.Vv, 71.15.Nc

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