| Summary: | 碩士 === 國立成功大學 === 微電子工程研究所碩博士班 === 98 === This thesis focuses mainly on the growth of one-dimensional (1D) ZnSe-based nanostructures by molecular-beam epitaxy (MBE), including ternary ZnSe0.95Te0.05 nanotips, twinned ZnSe0.9Te0.1 nanotips, ZnSe/ZnSeTe superlattice nanotips, and three-dimensional (3D) branched ZnSe/ZnSeTe heterostructure nanotips. Furthermore, the fabrication of ZnSeTe nanotip-based Metal-Semiconductor-Metal (MSM) photodetector was demonstrated.
ZnSe0.95Te0.05 nanotips were grown on Si(100) substrates by MBE system in the vapor-liquid-solid (VLS) growth process with an Au-based nanocatalyst. Average length of ZnSe0.95Te0.05 nanotips was 0.9 μm. The as-grown ZnSe0.95Te0.05 nanotips exhibited mixture of cubic zinc-blende and hexagonal wurtzite structures. With 5% Te incorporation, it was found that 20K photoluminescence (PL) peak red-shifted by 27 nm. Furthermore, ZnSe0.9Te0.1 nanotips were also grown by the same method. It was found that the as-grown ZnSe0.9Te0.1 nanotips were twinned with alternative multi-domains and mixture of cubic zinc-blend/hexagonal wurtzite phases. For the fabrication of ZnSe0.9Te0.1 nanotip photodetector, a thick Au film was deposited through an interdigitated shadow mask onto the ZnSe0.9Te0.1 nanotips by electron beam evaporation to serve as the contact electrodes. The measured photocurrent to dark current contrast ratio was larger than 700 with 5 V applied bias.
1D nanostructures with great complexity were also achieved. ZnSe/ZnSeTe superlattice nanotips with various well widths (Lw) were grown successfully. It was found that the ZnSe/ZnSeTe superlattice nanotips also exhibit mixture of cubic zinc-blende and hexagonal wurtzite structures. The observed PL intensities were much larger than that observed from the homogeneous ZnSeTe nanotips. Furthermore, the activation energies for the ZnSe/ZnSeTe nanotips with well widths of 16, 20 and 24 nm were 76, 46 and 19 meV, respectively. Based on the above-mentioned architecture, 3D branched ZnSe/ZnSeTe heterostructure nanotips were grown accordingly, in which the backbones and branches were composed of axial ZnSe/ZnSeTe heterostructures and ZnSe, respectively. PL spectra of the branched ZnSe/ZnSeTe nanotips present a visible blue-green emission at around 2.53 eV (490 nm) at low temperature, and the observed smaller PL intensity could be attributed to the formation of defects existing in the branches and/or the interfaces between backbone and branches.
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