N. Zainal

Growth of Vertically Aligned ZnO Nanorods Arrays by Hydrothermal Method

Well-aligned ZnO nanorod arrays with different average diameters were grown on silicon (100) substrates by hydrothermal method via the precursors of zinc nitrate hexahydrate (Zn (NO3)2 .6H2O) and Hexamethylenetetramine (C6 H12N4) with equal molar concentration at 0.025 mol/l and 0.05 mol/l. The ZnO nanorods were characterized by X-ray diffraction (XRD) and field emission Scanning electron microscopy (FE-SEM). XRD results indicated that all the ZnO nanorods were preferentially grown along [000 direction (c-axis). field emission Scanning electron microscopy images showed that the well-faceted hexagonal ZnO nanorods were grown vertically from the silicon (100) substrates.

Improvement of Porous GaAs (100) Structure through Electrochemical Etching Based on DMF Solution

We report on the fabrication of porous GaAs (100) using three different acids, H2SO4, HF, and HCl, diluted in DMF based solutions. The mixture of H2SO4 with DMF showed the best porous structures in comparison to other acids. The concentration of the DMF solution was then varied for a fixed concentration of H2SO4. It was apparent that the different concentration of the DMF solvent gave different types of morphology of the porous GaAs. Furthermore, a higher current density improved the uniformity of the pores distribution. The best porous GaAs exhibited well-defined circular shaped pores with high uniformity. To the best of our knowledge, such structure produced in such manner has never been reported so far. Finally, the optimum etching conditions of the pores were proposed.

Simulation of high performance quantum well GaN-based LED

The performance of quantum well GaN/AlGaN light emitting diode (LED) is reviewed for three different barrier compositions; symmetric barrier composition with low Al content, asymmetric barrier composition with higher Al content on p-type cladding layer and lower Al content on n-type cladding layer, and symmetric barrier composition with higher Al content. The study was conducted using ATLAS/BLAZE & LUMINOUS software developed by Silvaco International Inc. Integrated radiative recombination rate was studied on applied voltages up to 5V. Results showed three phases of LED performance with different applied voltages and these were explained using bandgap theory. I-V characteristic for each design agrees with the total additional voltage drop equation for a quantum well structure. The dominant radiative recombination rate regions in LED at low and high supplied voltages are also presented for the best performance LED design.

Fabrication of porous aluminium nitride films on silicon substrate for a better overgrown layer

Abstract In this work, properties of aluminium nitride films grown on Si substrates with two different thicknesses were investigated. From our observations, the aluminium nitride film with the thickness of ∼122 nm exhibited a better characteristic than the aluminium nitride film grown at ∼80 nm. Further, the sample with thicker aluminium nitride film was fabricated into porous structures using photoelectrochemical etching with a diluted sodium hydroxide electrolyte. As witnessed under field emission scanning electron microscopy, the formation of porous structures can be observed even though they are few and not uniformly distributed on the surface. Moreover, defect clusters and grain boundaries in the porous sample disappeared after the etching process, thus giving a narrower peak in X-ray diffraction rocking curve measurement. This work is a starting point towards establishing the technology of fabricating porous aluminium nitride to make it useful as a template for the subsequent growth.

Electrical and Optical Characterization of Mg doping in GaN

Apossible evidence of Mg related emission in Mg doped GaN material is observed inoptical measurement, even without thermal annealing. Meanwhile, the electrical properties of the sample improve when Ni/Au contact layer was annealed up to 400°C, but degrade at further temperature. We propose that such behavior isrelated to degradation of surface morphology of metal contact at higher temperature.

Characterization of GaN p-n Junction Grown on Si (111) Substrate by Plasma-Assisted Molecular Beam Epitaxy

In this report, the growth of GaN p-n junction on Si (111) substrate by plasma-assisted molecular beam epitaxy (PAMBE) is demonstrated. Doping of the GaN p-n junction has been carried out using Si and Mg as n-type and p-type dopants, respectively. Silicon substrate is used to grow the GaNpn-junction. In order to improve the crystalline quality of the nitride based junction, AlN is used as a buffer layer. The optical properties of the sample have been characterized by photoluminescence (PL) and Raman spectroscopy.PL spectrum shows a strong band edge emission of GaN at ~364nm, indicating good quality of the sample.The presence of peak ~657cm-1 in Raman measurement has exhibited asuccessful doping of Mg in the sample. The structural properties are measured by high-resolution x-ray diffraction (HR-XRD) and scanning electron microscopy (SEM). The cross section of the SEM image of the sample has shown sharp interfaces.

Optimization of InGaN Based Light Emitting Diodes

The performance of InGaN quantum well based Light Emitting Diodes; (LEDs) had been numerically investigated by using standard industrial software, Silvaco. In this work, we found that InGaN single quantum well (SQW) LEDs gives better performance than InGaN triple quantum wells LEDs. The simulation results suggest that the inhomogeneity of electron and hole distributions in quantum wells active region plays an important role in the LEDs performance. The threshold current per μm also increases as the number of quantum well is increased.