Nanofabrication and characterization of semiconductor quantum dot active regions

To achieve the theoretical advantages of ideal QDs, self-assembled QDs have been widely investigated as a method. The MOCVD and MBE grown semiconductors (III-Vs) based on self-assembled QDs, which are formed by the well known Stranski-Krastanow (SK) growth mode, have shown some promise to fulfill the theoretical potentials of ideal QDs. However, these structures lack full 3D carrier confinement due to the inevitable forming of a wetting layer. The inherent wetting layer present in SK QDs complicates achieving ideal performance from QD device structures such as high optical gain and low temperature sensitivity.;The work presented here focused on new QD active regions, to achieve full 3D carrier confinement within the QDs, using the nano-patterning by cylinder-forming diblock copolymer (PS-b-PMMA) combined with selective MOCVD growth to form the QDs. The diblock copolymer nano-patterned GaAs QD with a 12 nm diameter peak distribution showed as high density as 5.5--6.9 x 1010/cm2.;Since diblock copolymer lithography enables us to modify nanostructures of QD, a controlled selective MOCVD growth was possible to form a three-layered QD structure inside the patterned holes. The diblock copolymer nano-patterned three-layered InGaAs QDs (lambda ∼ 1.6 mum) using quarternary (InGaAsP) Separate Confinement Heterostructure (SCH) were grown by MOCVD, systematically analyzed, and incorporated into the QD laser device. In particular, the three-layered InGaAs QD structures (InGaAsP/InGaAs/InGaAsP) exhibited good wavelength controllability over a wide range within the telecommunication bands and accomplished room temperature photoluminescence (PL). In addition, three-layered InGaAs QD structures sandwiched by InP barriers exhibit approximately 90 times enhancement of PL intensity compared to the previous structure with InGaAsP barriers, possibly due to its better carrier confinement property. These structures also demonstrate a PL spectral peak with significantly narrower FWHM (∼ 34 meV) compared to recent reports of patterned QDs fabricated by other methods. Finally, by incorporating the three-layered InGaAs QD structure into a laser structure, the laser oscillation was demonstrated for the first time from nano-patterned active regions on an InP substrate. For a future application of diblock copolymer lithography, intersubband quantum box lasers were considered and its Active Photonic Crystal (APC) structure was designed.