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Defect Structure of Strained Heteroepitaxial In (1—x) Al (x) P Layers Deposited by MOVPE on (001) GaAs Substrates
Author(s) -
Wagner G.
Publication year - 1998
Publication title -
crystal research and technology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.377
H-Index - 64
eISSN - 1521-4079
pISSN - 0232-1300
DOI - 10.1002/(sici)1521-4079(1998)33:3<383::aid-crat383>3.0.co;2-v
Subject(s) - nucleation , slip (aerodynamics) , partial dislocations , crystallography , materials science , condensed matter physics , dislocation , transmission electron microscopy , lüders band , relaxation (psychology) , metalorganic vapour phase epitaxy , chemistry , composite material , epitaxy , nanotechnology , layer (electronics) , physics , psychology , social psychology , organic chemistry , thermodynamics
Weak‐beam, large angle convergent beam electron diffraction and high resolution transmission electron microscope experiments have revealed, that after strain relaxation due to plastic deformation dislocation networks can be observed in In (1—x) Al (x) P heteroepitaxial layers grown on (001) GaAs substrates under compressive stress. The 60° slip dislocations are mostly dissociated into partials of Shockley type whereas in the particular case of layers grown under tension twins are predominantly formed by successive nucleation and slip of 90° Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90° Shockley partials pile up during extension of twins, then planar incoherent twin boundaries with {112} coincidence planes have been formed during strain relaxation. Due to the space group symmetry ((InAl)P belongs to the space group F 4‐3 m ) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and (1‐1‐1) slip of the [1‐10] zone are preferred to nucleation and slip on the {111} planes of the [110] zone. Apparently, the occupacy of the atomic sites in the dislocation core with either group‐III or group‐V atoms is responsible for this behaviour. The nature of the defects implies that their spontaneous nucleation should have taken place at the growing surface. Under tensile strain the 90° Shockley partial is nucleated first and the 30° one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30° partial, i.e. the partial with less mobility or with higher friction force, is detained near or directly in the interface. Thus, in layers grown under tension the stacking fault associated with the dissociated 60° dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary layer.