Defect structure of strained heteroepitaxial In(1-x)Al-(x)P layers deposited by MOVPE on (001)GaAs substrates

摘要

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 degrees 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 degrees Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90 degrees 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 F43m) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and ((1) over bar (1) over bar 1) slip of the [(1) over bar 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 degrees Shockley partial is nucleation first and the 30 degrees one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30 degrees 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 degrees dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary laver. [References: 35]