  The control over the structural homogeneity is of paramount importance for
ternary nitride compounds - the second most important semiconducting
material-class after Si, due to its unrivalled applicability in
optoelectronics, and high power/high frequency electronics. Therefore it is
timely to investigate possible mechanisms influencing the crystallographic
constitution of the material. In this work the diffusion mechanism of manganese
in gallium nitride is investigated in two types of epilayers: Mn implanted
metalorganic vapour phase epitaxy grown GaN and (Ga,Mn)N solid solution grown
by molecular beam epitaxy. The extent of the Mn diffusion is established by
secondary ion mass spectrometry. Analysis of the Mn profiles in the implanted
samples in the frame of the infinite source diffusion led to the establishment
for the first time of the pre-exponential factor DO = 2x10-4 cm2/s and
diffusion activation energy EA = 1.8 eV describing the diffusion coefficient of
Mn in GaN. Modelling of the out-diffusion of Mn from (Ga,Mn)N layers based on
these values in turn allows to provide an explanation of the origin of the
ubiquitously observed near-the-surface sizable depletion of Mn in (Ga,Mn)N,
resulting from the blocking of the Mn out-diffusion by Mn-oxide and the
correspondingly formed space-charge layer on the surface.
