2, Pontifícia Universidade Católica do Rio de Janeiro, Rio de Janeiro, , Brazil
The ordering of the group III elements in InxGa1-xP (x=0.5) have been observed to vary during the growth of GaAs quantum well and InAs quantum dot structures grown on InGaP by metalorganic vapor phase epitaxy. The effect of crystal polarity on ordering has been established using high angle annular dark imaging in the scanning transmission electron microscopy. Ordering is observed along <110> projections when the dumbbell configurations show the group V element on top of the group III element. For GaAs quantum wells on InGaP, ordering is maintained throughout the growth process. However, when InAs quantum dots are grown and then covered with a thin GaAs layer, ordering is not observed in the InGaP on top of the GaAs layer. It is observed that after a few nanometers of growth, ordering resumes. We attribute this to compositional pulling effects, where some excess indium in the gas phase is necessary to grow the InAs quantum dot. The excess indium is eventually consumed in the InGaP and ordering resumes when the intended composition is achieved. Cathodoluminescence has been used to correlate the electronic properties with the microstructure of our thin film structures.