The research presented in this dissertation pioneered three novel nano-material systems, including vertically aligned InAlAs nanowires (NWs) on two-dimensional (2-D) graphene, InAs NWs on 2-D MoS2, and GaAsP NWs on Si using metalorganic chemical vapor deposition (MOCVD). Bottom up integratiton of NW structures enable heteroepitaxy of largely dissimilar III-V compounds on foreign substrates and provide a basis for design of high-performance devices that are otherwise inaccessible using thin- films or planar geometries. During conventional heteroepitaxy of planar geometries, strict constraints are imposed by the need to match lattice parameters, thermal expansion coefficients, and polar coherence between adjacent dissimilar materials. Semiconductor III-V NWs with small substrate footprints can permit relief of lattice mismatch-induced strain in heteroepitaxial systems. Thus, high crystalline quality III-V compound semiconductor NWs can be monolithically integrated with foreign substrates for novel electronic and optoelectronic device designs.
This dissertation presents wafer-scale production of vertically oriented InAsyP1-y and InxAl1-xAs NWs on single layer graphene (SLG) and MoS2 substrates, grown via pseudo-van der Waals epitaxy (vdWE). The morphology, areal density, and crystalstructure of InAsyP1-y NWs within the 1 ≤ y ≤ 0.8 range and InxAl1-xAs in the 1 ≤ x ≤ 0.5 range are quantitatively analyzed by mapping a wide growth parameter space as a function of growth temperature, V/III ratio, total precursor flow rate, and molar flow ratio of precursors. Furthermore, through manipulation of growth kinetics, selective-area vdWE of III-V NWs on 2-D MoS2 surfaces is demonstrated, and pattern-free positioning of single NWs on isolated MoS2 micro-plates with one-to-one NW-to-MoS2 placement is highlighted. Here, the highest axial growth rate of 840 nm/min and NW number density of ∼8.3 × 108 cm−2 for vdWE of high aspect ratio (> 80) InAs NW arrays on graphitic surfaces is reported.
Additionally, selective-area epitaxy (SAE) of GaAsP-GaP core-multi shell NW arrays on patterned Si(111) substrates is reported. The composition of GaAsyP1-y NWs is tuned toward a targeted value of y = 0.73 to achieve the bandgap of 1.75 eV. The effect of growth rate on morphology, total yield, and symmetric yield of GaAsP NWs is explored through modulation of the effective local supply of growth species. Under the optimized SAE growth condition, > 90% yield of hexagonally symmetric GaAsP NWs on Si is realized using a 100 μm × 100 μm field of nano-hole arrays in the center of a 400 μm × 400 μm mesa with border width of 100 μm.
|Advisor:||Mohseni, Parsian K.|
|Commitee:||Hirschman, Karl D., Hubbard, Seth M., Kurinec, Santosh K.|
|Subjects:||Engineering, Materials science|
|Keywords:||Epitaxy, Graphene, III-V Semiconductor, Molybdenum disulfide, Nanowire|
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