Fabrication of Low-Dimensional Structures in III-V Semiconductors
Sammanfattning: The thesis presents studies on the processing technology and the characterization of nanometer-sized and low-dimensional structures in III-V semiconductors. Two major approaches are described: 1) the combination of aerosol technology and plasma etching for the fabrication of quantum dots (QDs) in InP-based materials and 2) the use of high-resolution electron beam lithography and plasma or wet chemical etching to make quantum well wires (QWWs) in both GaAs and InP-based structures. The first approach is based on parallel processing technology for the formation of arrays of QDs in an InP/GaInAs quantum well structures using aerosol-deposited masks and low-energy plasma etching. The deposition of Ag aerosol particles, 20 to 80 nm in size, with an extremely narrow size distribution, allows the formation of etch masks with densities up to 10E9 cm-2. These masks are stable under electron cyclotron resonance (ECR) plasma conditions in a CH4/H2/Ar discharge and allow the formation of arrays of QDs, 25-100 nm in size, with densities of about 10E9 cm-2. The QDs produced were investigated using scanning electron microscopy, photo- and cathodoluminescence and other methods. The second approach is more "traditional", in the sense that the processing of an individual structure is utilized. To define QWWs or QDs, high-resolution electron beam lithography and a subsequent pattern transfer by plasma or wet etching was used. QWWs in InP/GaInAs and GaAs/GaInAs material were produced by ECR plasma and wet etching for spectroscopy studies. A single 50 to 90 nm wide QWW (quantum point contact-QPC) was fabricated in a modulation-doped InP/GaInAs, lattice-mismatched structure. The epitaxially regrown QPC demonstrated a quantized conductance at temperatures of 10K and above, which indicated that the fabricated structure was of high quality. Studies of damage induced in GaAs/AlGaAs and GaAs/GaInP heterostructures by an ECR plasma have also been performed. The damage was characterized by photoluminescence, transport measurements and electron paramagnetic resonance. Experiments showed no correlation between the density of plasma-induced defects and transport or photoluminescence properties, nor between photoluminescence and transport properties.
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