Dislocation core structures in Si-doped GaN
1. Basic GaN characterization data
AFM images were acquired in tapping mode on a Veeco Dimension 3100 microscope in order
to calculate the threading dislocation densities from the densities of pits at the surfaces of the
silane-treated GaN films [1]. The results show that threading dislocation densities (TDDs)
measured for Si-doped samples were slightly higher than those reported for the undoped GaN
samples [2]. The densities increased from (6.0 ± 0.6) × 109 cm-2 for HDD undoped GaN to (10
± 1) × 109 cm-2 for HDD highly Si-doped GaN, and from (2.7 ± 0.5) × 108 cm-2 for LDD
undoped GaN to (5 ± 1) × 108 cm-2 for LDD Si-doped GaN [2]. This slight increase in
dislocation density with increasing Si-doping has been observed previously and has been
attributed to the segregation of Si at dislocation cores [2] which inhibits dislocation movement
by climb, thereby limiting the reaction and annihilation of dislocations in Si-doped GaN,
resulting in higher dislocation densities [3].
Weak-beam dark-field (WBDF) microscopy on all samples was performed on a JEOL 4000
EX-II (400 keV) TEM. Figure S1 shows that the dislocations in the near-surface region of both
the undoped GaN films and the low dislocation density Si-doped GaN film are oriented either
parallel to or very close to the [0001] direction. However, Figure S2 shows that some (a+c)type dislocations tilt on passing the undoped/high Si-doped GaN interface at approximately 8
± 4o. The bending of dislocations in Si-doped GaN has been observed previously [2] [4] [5] [6]
[7] [8] [9] [10] and linked to higher tensile stresses in the films, which have been associated
with the inhibition of climb [2], SiNx masking [11] [12], strain relaxation [4] [5], the interaction
of bent dislocations with planar defects [6], surface roughness [7], electronic effects [8] [13]
and to surface mediated climb [9].
2. Computational methods and results
Large simulation cells were used containing a quadrupolar dislocation arrangement containing
core structures previously observed in undoped, unstrained GaN films [14], before the tensile
stress of 1.18 GPa, calculated using the modified Stoney's formula [15] on in-situ wafer
curvature measurements reported previously by Moram et al. [2] was applied to large
simulation cells and the relaxed structures are shown in Figure S3. Cells were relaxed using a
modified Stillinger-Weber potential [16] that has been widely used to study dislocations in
GaN [14] [17].
Figure S1: Cross-sectional weak-beam dark field TEM images acquired for the (a) high
dislocation density undoped GaN sample when g = ( 1120 ), g-3g diffraction condition was
excited and low dislocation density (b) undoped and (c) low Si-doped GaN when the g = (
), g-2g diffraction condition was excited.
Figure S2: Cross sectional WBDF images of the same area of a high dislocation density Sidoped (1 × 1019 atoms/cm3) GaN film showing tilted (a+c)-type dislocations when either (a) g
=(
) or (b) g = (0002) diffraction conditions were excited. The tilted dislocations are
indicated with arrows.
Figure S3: Molecular dynamics simulations viewed in the (0001) plane showing (a) (a+c)-type
double 5/6-atom core, (b) (a+c)-type dissociated 7/4/8/4/9-atom core and a-type 5/7-atom core
after stress values of 1.175 GPa were applied to GaN simulation cells using the Open
Visualization Tool [18]. White spheres represent Ga atoms and dark spheres represent N
atoms.
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