Research On The Synthesis And Photoelectric Properties Of Several One Dimensional Semiconductor Alloy Nanostructures

In the past two decades, one dimensional (1D) semiconductor nanostructuresaroused considerable attention. Especially,1D semiconductor alloy nanostructuresbecome the focus of research because of the tunable photoelectrical properties. In ourdissertation, several one1D semiconductor nanostructures and1D alloynanostructures such as high-quality CdTe and ZnTe nanowires, composition-tunableCdZnTe alloy nanostructures, CdZnSeTe alloy nanobelts as well as bandgap broadlytunble ZnGaAsSe alloy nanaowires were achieved by modified chemical vapordeposition (CVD) method. In addition, the titanium dioxide nanorod array bundleswere synthesized by the hydrothermal method. The morphologies, compositions, andstructure information of these as-prepared nanostructures were characterized. We alsostudied their photoluminescence, wave guiding and surface photovoltage by Scanningnear-field optical microscope (SNOM) and surface photovoltage system. The mainnovel points are shown as follows：1. High-quality CdTe and ZnTe nanowires were synthesized by a modifiedchemical vapor deposition (CVD) method. Both CdTe and ZnTe nanowires are wellcrystallized and homogeneously exhibit a zinc-blende crystal structure. The Surfacephotovoltage measurements of the CdTe nanowires show that the as-grown CdTenanowires have a broad response band cover the entire visible region. The opticalproperties of individual ZnTe nanowires show that these ZnTe nanowires have intensenear-bandgap emission as well as good waveguide behavior. The peak wavelength ofthe emission bands show a red-shift behaviour afer transported along the ZnTenanowire.2. Semiconductor alloy nanostructures with tunable compositions provideexcellent material platforms for function-tunable and/or broadband-responseoptoelectronic applications. Here we report the growth of high quality single-crystalline Cd1-xZnxTe alloy nanostructures in the full-composition region on a singlesubstrate via a simple one-step co-thermal evaporation route. X-ray diffraction (XRD)and transmission electron microscopy (TEM) characterizations confirm that the latticeparameters gradually increase with the decrease of cadmium contents.Photoluminescence (PL) measurements show that these composition-tunable alloynanostructures exhibit near-bandedge emissions, with peaks wavelength continuously changing from554nm to819nm. These alloy nanostructures will find potentialapplications in near-infrared function-tunable optoelectronic devices, such ashigh-performance solar cells, variable-wavelength photodetectors and so on.In addition, we also obtained ZnCdTe alloy nanostructures by a two-step method.Interestingly, the synthesized products also consist of some brance alloynanostructures besides the alloy nanowires. The microstructures imformation of thebranced nanostructures were characterized by TEM, and reveal that the trunk andbranch are uniform in composition but possess different growth direction. In addition,an ion exchange model is proposed to illustrate the formation of the alloy nanowiresand branch alloy nanostructures. These branch alloy nanowires will find potentialapplication in integrated photoelectronic components.3. Based on the simple CVD route, we have growth ZnCdSeTe quaternary alloynanobelts. The SEM results show that these as-grown products were tapered nanobelts.XRD reveal that these ZnCdSeTe alloy nanobelts have zinc-blende crystal structure.The microstructures imformation of these ZnCdSeTe alloy nanobelts werecharacterized by TEM, and show that these quaternary alloy nanobelts were wellcrystallized with the preferentially growing direction of [111]. The EDS resultsindicate the synthesized nanobelts are Cd0.15Zn0.85Se0.86Te0.14quaternary alloynanobelts. Under laser excitation, these alloy nanobelts exhibit an emission bandaround570nm, which originate from the band-band transition of the quaternary alloynanobelts.4. Composition-tunable semiconductor alloy nanowires are emerging as animportant class of materials for the realization of high-performance laterally arrangedmultiple bandgap (LAMB) solar cells. Here we report the first growth of GaZnSeAsquaternary alloy nanowires with tunable comppositions by a temperature/space-selective CVD route. Under laser excitation, these special quaternary alloynanowires exhibit composition-related characteristic emissions, with peak wavelengthgradually tunable from470nm (2.64eV) to832nm (1.49eV), covering almost theentire visible spectrum. Surface photovoltage measurement further reveals that thesealloy nanowires have tunable bandgaps along the length of the substrate, making thempromising candidates for developing high-efficiency LAMB solar cells.5. TiO2nanorod array bundles were synthesized by the hydrothermal method.Interestingly, the mount of the precursors have an important influence on themorphology of the product. The surface photovoltage measurements show that TiO2nanorod array bundles show higher surface photovoltage response under positive bias, on the contrary, the negative bias can weaken surface photovoltage response of theTiO2nanorod array bundles.