FABRICATION OF MESOSCOPIC SEMICONDUCTOR STRUCTURES

The fabrication of nanoscale III-V compound semiconductor structures is studied in this thesis. Self-organizing quantum dot structures were realized in hydride vapor phase epitaxy (VPE) by utilizing strain-induced 3-dimensional growth. In the experiments the optimum growth window for a material combination of InP on GaAs was determined. In addition to the growth conditions, the island density was found to depend strongly on the surface step density, which made it possible to control spatially the growth. For the control, the step density was locally increased by bombarding substrates by focused ion beam (FIB) prior to growth. By enhancing locally the nucleation probability, homogeneous InP wires on GaAs were realized. The self-organizing growth of nanoscale InP islands on GaAs was also studied in metalorganic vapor phase epitaxy (MOVPE). To be able to modify the properties of the islands, the viability of selective growth of thin InGaAs layers on these islands to form nanoscale heterostructures was demonstrated by MOVPE. In-situ formation of gold island mask by molecular beam epitaxy (MBE) for reactive ion etching (RIE) of nanoscale columns was demonstrated. Using this method, sub-100 nm GaAs/AlGaAs columns with high aspect ratio were produced. A review of several other methods used to create nanoscale semiconductor structures is also included.