Growth and characterisation of site-controlled InAs/InP quantum dots by droplet epitaxy in MOVPE

InAs/InP quantum dots were grown by droplet epitaxy via metal-organic vapor phase epitaxy (MOVPE). Their structural and optical properties on a planar substrate were extensively investigated. Indium droplets were formed through pyrolysis of trimethylindium and by controlling parameters such as deposition temperature, flow rate and growth interrupt, the density and size of droplets could be manipulated to form optically active quantum dots (QDs) in the 1550nm telecom emission band. After optimising the conditions for QD formation on planar substrates, site-control of the QDs was investigated. The major emphasis of this work and its findings is the deterministic positioning of QDs through the precursor process of positioning of indium droplets within ex-situ fabricated nanohole arrays. Using electron beam lithography and dry etching, nanohole arrays were fabricated, which served as favourable nucleation sites for droplets and subsequently QDs through the process of arsenic crystallisation. Following nanohole fabrication, extensive optimisation of the surface cleaning procedure and buffer growth were developed to reduce impurity levels and obtain high-quality QDs. The spatial arrangement of droplets deviates from randomness when the patterned substrate is employed as a template for growth. This is a new method to site-control QDs by deterministic positioning of droplets in droplet epitaxy.