Growth mechanism of GaAs microdisk structures by area-selective epitaxy using migration-enhanced epitaxy

We have carried out area-selective epitaxy of GaAs microdisk structures on a SiO2-masked GaAs substrate by migration-enhanced epitaxy. We have successfully grown "damage-free" disks at 590 °C. It is found that, for the structures grown on (111)B substrates, the facets surrounding the disks are controlled by the V/III beam equivalent pressure ratio. This characteristic is caused by the reduced growth rate in the [111]B direction under high V/III ratios. Using an optimized growth condition, uniform hexagonal GaAs disks surrounded by six vertical {110} facets and a flat (111)B top are grown. The microdisks grown on (001) substrates, however, show no flat-top structures, regardless of the V/III ratio, probably due to the fact that the growth rate in the (001) direction is not sensitive to the V/III ratio. In the latter case, square-pyramidal structures surrounded by four inclined {011} facets are obtained.