ElÚ SAV pozýva na prednášku prof. Pierra Ruterana, (Centre de Recherche sur les Ions, les Matériaux et la Photonique (CIMAP), Univ. Caen, Normandie): Dislocations and inversion domains in the wurtzite structure: a case study by HRTEM in GaN and ZnO
Dňa 28. 6. 2022, 13,00 hod., veľká zasadačka ElÚ SAV.
Abstrakt:
Using high-resolution electron microscopy, atomistic calculations, and image simulations, we have investigated the atomic structures of the most common extended defects in nitrides and ZnO. In this talk, I shall focus on the a=1/3[11̅20] edge threading dislocations and inversion
domains. In nitride layers (AlN, GaN, InN), the atomic structure of a edge dislocation was found
to exhibit 5/7, 8 or 4 atom cycles. The two first atomic configurations were observed at a similar
frequency for isolated dislocations and low-angle boundaries. The tilt coincidence grain
boundaries around the conventional [0001] growth direction have been also been studied. The
most frequent configurations are made of 5/7 and 8 atom cycles. However, the reconstruction
of some boundaries was only possible by taking into account the occurrence of structural units
which include 4-atom ring cycles. In non-symmetric interfaces, a new structural unit made of
5/4/7 atom rings constitutes the core of grain boundary dislocations. More generally, our
topological analysis has shown that in these wurtzite semiconductors, depending on the tilt
angle, the situation is more complicated. In nitrides, the structural units are only made of
individual a edge dislocations, and the Burgers vectors adapt their orientation in order to
accommodate for the grain boundary tilt angle. However, in ZnO, the topology imposes the type
of the grain boundary dislocations and in addition to the a edge dislocation, the [10̅10]
dislocation also becomes a central brick in the construction of the boundaries. Its atomic
structure is a close combination of 4/8/6 atom cycles in agreement with the early theoretical
report1 made of two adjacent a edge dislocations and it exhibits a large core which
accommodates for the tilt angle. The case of inversion domains is also interesting: they take
place mainly inside (10-10) planes when they form during the growth along [0001]. In the basal
plane, they occur upon heavy doping with magnesium and lead to an irregular and stepped
interface. Interestingly at the GaN/ZnO, a specific growth mode was found lead to an abrupt
change of polarity within one monolayer as shown by ABF analysis.
1 Osipian et Smirnova Phys. Stat. Sol. 80, 19 (1968)
