Amira Saryati Ameruddin

Nanowires Grown on InP (100): Growth Directions, Facets, Crystal Structures, and Relative Yield Control

Growth of III-V nanowires on the [100]-oriented industry standard substrates is critical for future integrated nanowire device development. Here we present an in-depth analysis of the seemingly complex ensembles of epitaxial nanowires grown on InP (100) substrates. The nanowires are categorized into three types as vertical, nonvertical, and planar, and the growth directions, facets, and crystal structure of each type are investigated. The nonvertical growth directions are mathematically modeled using a three-dimensional multiple-order twinning concept. The nonvertical nanowires can be further classified into two different types, with one type growing in the ⟨111⟩ directions and the other in the ⟨100⟩ directions after initial multiple three-dimensional twinning. We find that 99% of the total nanowires are grown either along ⟨100⟩, ⟨111⟩, or ⟨110⟩ growth directions by {100} or {111} growth facets. We also demonstrate relative control of yield of these different types of nanowires, by tuning pregrowth annealing conditions and growth parameters. Together, the knowledge and controllability of the types of nanowires provide an ideal foundation to explore novel geometries that combine different crystal structures, with potential for both fundamental science research and device applications.

InxGa1?xAs nanowires with uniform composition, pure wurtzite crystal phase and taper-free morphology

Obtaining compositional homogeneity without compromising morphological or structural quality is one of the biggest challenges in growing ternary alloy compound semiconductor nanowires. Here we report growth of Au-seeded InxGa1-xAs nanowires via metal-organic vapour phase epitaxy with uniform composition, morphology and pure wurtzite (WZ) crystal phase by carefully optimizing growth temperature and V/III ratio. We find that high growth temperatures allow the InxGa1-xAs composition to be more uniform by suppressing the formation of typically observed spontaneous In-rich shells. A low V/III ratio results in the growth of pure WZ phase InxGa1-xAs nanowires with uniform composition and morphology while a high V/III ratio allows pure zinc-blende (ZB) phase to form. Ga incorporation is found to be dependent on the crystal phase favouring higher Ga concentration in ZB phase compared to the WZ phase. Tapering is also found to be more prominent in defective nanowires hence it is critical to maintain the highest crystal structure purity in order to minimize tapering and inhomogeneity. The InP capped pure WZ In0.65Ga0.35As core-shell nanowire heterostructures show 1.54 μm photoluminescence, close to the technologically important optical fibre telecommunication wavelength, which is promising for application in photodetectors and nanoscale lasers.

Bandgap Energy of Wurtzite InAs Nanowires

InAs nanowires (NWs) have been grown on semi-insulating InAs (111)B substrates by metal-organic chemical vapor deposition catalyzed by 50, 100, and 150 nm-sized Au particles. The pure wurtzite (WZ) phase of these NWs has been attested by high-resolution transmission electron microscopy and selected area diffraction pattern measurements. Low temperature photoluminescence measurements have provided unambiguous and robust evidence of a well resolved, isolated peak at 0.477 eV, namely 59 meV higher than the band gap of ZB InAs. The WZ nature of this energy band has been demonstrated by high values of the polarization degree, measured in ensembles of NWs both as-grown and mechanically transferred onto Si and GaAs substrates, in agreement with the polarization selection rules for WZ crystals. The value of 0.477 eV found here for the bandgap energy of WZ InAs agrees well with theoretical calculations.

Understanding the growth and composition evolution of gold-seeded ternary InGaAs nanowires

InGaAs nanowires offer great promise in fundamental studies of ternary compound semiconductors with variable composition and opens up a wide range of applications due to their bandgap tunability and high carrier mobility. Here, we report a study on the growth of Au-seeded InGaAs nanowires by metal-organic vapour phase epitaxy and present a model to explain the mechanisms that govern the growth and composition evolution in ternary III-V nanowires. The model allows us to further understand the limitations on the growth rate and incorporation of the two group III species imposed by the deposition conditions and some intrinsic properties of the material transport and nucleation. Within the model, the evolution of InGaAs nanowire growth rate and composition with particle size, temperature and V/III ratio is described and correlates very well with experimental findings. The understanding gained in this study should be useful for the controlled fabrication of tunable ternary nanowires for various applications.

Hydrophobic rutile phase TiO2 nanostructure and its properties for self-cleaning application

The nanostructured hydrophobic rutile phase titanium dioxide TiO2 and its properties for self-cleaning application were directly synthesized from titanium butoxide (TBOT) precursor deposited on the fluorine doped tin oxide (FTO) substrate through the hydrothermal treatment with different volume of TBOT and adding of Cetyl Trimethylammonium Bromide (CTAB). The samples were characterized respectively by way of field-emission scanning electron microscopy (FE-SEM), water contact angle measurement and Raman spectroscopy for surface analysis system. The FE-SEM results revealed a layer of nanoparticles were growth on the FTO substrate. The surface properties of the samples were studied with a water contact angle measurement. The water contact angle measurement results revealed the hydrophobic of samples as the angle of water droplet on the sample increased. The rutile phase and surface of TiO2 were confirmed using a Raman spectroscopy.The nanostructured hydrophobic rutile phase titanium dioxide TiO2 and its properties for self-cleaning application were directly synthesized from titanium butoxide (TBOT) precursor deposited on the fluorine doped tin oxide (FTO) substrate through the hydrothermal treatment with different volume of TBOT and adding of Cetyl Trimethylammonium Bromide (CTAB). The samples were characterized respectively by way of field-emission scanning electron microscopy (FE-SEM), water contact angle measurement and Raman spectroscopy for surface analysis system. The FE-SEM results revealed a layer of nanoparticles were growth on the FTO substrate. The surface properties of the samples were studied with a water contact angle measurement. The water contact angle measurement results revealed the hydrophobic of samples as the angle of water droplet on the sample increased. The rutile phase and surface of TiO2 were confirmed using a Raman spectroscopy.

Fabrication of TiO2 nanostructures on porous silicon for thermoelectric application

Nowadays, technology is moving by leaps and bounds over the last several decades. This has created new opportunities and challenge in the research fields. In this study, the experiment is about to investigate the potential of Titanium Dioxide (TiO2) nanostructures that have been growth onto a layer of porous silicon (pSi) for their thermoelectric application. Basically, it is divided into two parts, which is the preparation of the porous silicon (pSi) substrate by electrochemical-etching process and the growth of the Titanium Dioxide (TiO2) nanostructures by hydrothermal method. This sample have been characterize by Field Emission Scanning Electron Microscopy (FESEM) to visualize the morphology of the TiO2 nanostructures area that formed onto the porous silicon (pSi) substrate. Besides, the sample is also used to visualize their cross-section images under the FESEM microscopy. Next, the sample is characterized by the X-Ray Diffraction (XRD) machine. The XRD machine is used to get the information about the...

Performance comparison between silicon solar panel and dye-sensitized solar panel in Malaysia

In carrying out experimental research in performance between silicon solar panel and dye-sensitive solar panel, we have been developing a device and a system. This system has been developed consisting of controllers, hardware and software. This system is capable to get most of the input sources. If only need to change the main circuit and coding for a different source input value. This device is able to get the ambient temperature, surface temperature, surrounding humidity, voltage with load, current with load, voltage without load and current without load and save the data into external memory. This device is able to withstand the heat and rain as it was fabricated in a waterproof box. This experiment was conducted to examine the performance of both the solar panels which are capable to maintain their stability and performance. A conclusion based on data populated, the distribution of data for dye-sensitized solar panel is much better than silicon solar panel as dye-sensitized solar panel is very sensitive to heat and not depend only on midday where is that is the maximum ambient temperature for both solar panel as silicon solar panel only can give maximum and high output only when midday.In carrying out experimental research in performance between silicon solar panel and dye-sensitive solar panel, we have been developing a device and a system. This system has been developed consisting of controllers, hardware and software. This system is capable to get most of the input sources. If only need to change the main circuit and coding for a different source input value. This device is able to get the ambient temperature, surface temperature, surrounding humidity, voltage with load, current with load, voltage without load and current without load and save the data into external memory. This device is able to withstand the heat and rain as it was fabricated in a waterproof box. This experiment was conducted to examine the performance of both the solar panels which are capable to maintain their stability and performance. A conclusion based on data populated, the distribution of data for dye-sensitized solar panel is much better than silicon solar panel as dye-sensitized solar panel is very sensiti...

Influence of InxGa1-xAs Underlying Layer on the Structural of the In0.5Ga0.5As Quantum Dots Grown by MOCVD

The single layer In0.5Ga0.5As quantum dots (QDs) were grown on a thin InxGa1-xAs underlying layer by metal-organic chemical vapor deposition (MOCVD) via Stranski-Krastanow growth mode. The effect of different indium composition in the InxGa1-xAs underlying layer was investigated using atomic force microscopy (AFM). AFM images show that the QDs structures were formed on the surface. The dots formation on the surface changes with different composition of InxGa1-xAs underlying layer. Increasing indium composition in the underlying layer resulted to formation of higher density and smaller size dots. Several large dots were also formed on the surface. Growing of underlying layer reduces the lattice mismatch between In0.5Ga0.5As and GaAs, and decreases the critical thickness of the dots. This strongly influences the dots nucleation on the surface. Growth of quantum dots using underlying layer is one way to modify dot formation in order to achieve uniform QDs of right size and high density, which are essential for QDs device applications.

Influence of growth temperature and V/III ratio on Au-assisted In x Ga 1−x As nanowires

InxGa1-xAs nanowires were grown using metal-organic chemical vapour deposition (MOCVD) with various growth temperatures and V/III ratios. The morphology of these nanowires and the composition distribution along the nanowire were studied as a function of these growth parameters. With higher growth temperature and lower V/III ratio, the tapering of the nanowires is reduced. However, the incorporation of Ga in the nanowires is also reduced with lower V/III ratio. The composition distribution along the nanowires is non-uniform with typically In-rich bases and Ga-rich tips.

Effect of InxGa1-xAs underlying layer and growth mode on the surface morphology of In0.5Ga0.5As/GaAs quantum dots

Single layer of In0.5Ga0.5As quantum dots (QDs) was grown using self‐assembled Stranski‐Krastanow on a thin InxGa1−xAs underlying layer and on a reference GaAs wafer by metal‐organic chemical vapour deposition (MOCVD). The effect of different indium composition in the underlying layer and the duration of arsine (AsH3) flow during cooling‐down period of the growth process were investigated and characterized using atomic force microscopy (AFM). The growth of the thin underlying layer has significant influence on the formation of the QDs on the top surface. The dots density increases with increasing indium composition in the underlying layer. AsH3 flow during the period was found to influence the nucleation process of In0.5Ga0.5As QDs. A shorter period of AsH3 flow promotes smaller dots size and therefore increases the dots density.