Abu Hassan Haslan

Significant Influences of Selenium on the Electrical Properties of Bi2Te3 Compounds Synthesized Using Solid-State Microwave Irradiation

The thermoelectric materials based on p-type Bi2Se3xTe3 (1-x) bulk products and dispersed with x compositions of Se (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) were fabricated using standard solid-state microwave synthesis procedures. The products were characterized by X-ray diffraction (XRD). The XRD characterizations revealed that these products are pure Bi2Te3 and Bi2Se3 with uniform structures. The electrical properties of the Bi2Te3, Bi2Se3 and Bi2Se3xTe3 (1-x) samples were measured in the temperature range of 303–523 K. The highest value of the Seebeck coefficient was 176.3 μV/ K for the Bi2Se0.6Te2.4 sample, but only 149.5 and 87.4 μV/K for the Bi2Te3 and Bi2Se3 samples, respectively.

Enhanced UV Photodetector Responsivity in Porous GaN/Si(111) by Metal-Assisted Electroless Etching

This paper presents the structural and optical studies of porous GaN sample compared to the corresponding as grown GaN. The samples were investigated by scanning electron microscopy (SEM), high resolution x-ray diffraction (HRXRD), and photoluminescence (PL). The porous area is very uniform, with pore diameter in the range of 80-110 nm. XRD measurements showed that the (0002) diffraction plane peak width of porous samples was slightly broader than the as-grown sample. PL measurements revealed that the near band edge peak of the porous samples were redshifted. Metal-semiconductor-metal (MSM) photodiode was fabricated on the samples. For as grown GaN sample, this detector shows a sharp cut-off wavelength at 362 nm. A maximum responsivity of 0.258 A/W was achieved at 360 nm. For the porous GaN sample, this detector shows a sharp cut-off wavelength at 364 nm. A maximum responsivity of 0.771 A/W was achieved at 363 nm.

Growth of Aligned ZnO Nanorods Grown on Polyethylene Naphthalate Substrates: Effect of the Growth Duration

Aligned ZnO nanorods were synthesized on a polyethylene naphthalate (PEN) substrates using a chemical bath deposition method. The growth temperature and precursor concentration were 95 °C and 0.025 M, respectively. The effects of growth duration (2 h to 8 h) on the optical and structural properties of the obtained ZnO nanorods on seed layer ZnO/PEN substrate were then investigated using X-ray diffraction, field-emission scanning electron microscopy (FESEM), and photoluminescence (PL) spectroscopy at room temperature. The high intensity of (002) peak compared with (100) and (101) in the X-ray diffraction (XRD) pattern demonstrated that the ZnO nanorods grown for 6.5 h had more vertical higher crystal quality than the samples grown for other durations. The average diameter of ZnO nanorods grown on PEN substrates increased from 19 nm to 45 nm with increased growth duration from 2 h to 8 h, respectively.

Fabrication and Characterization of Pb1-xYbxSe0.2Te0.8 Based Alloy Thin Films Thermoelectric Generators Grown Using Thermal Evaporation Method

In the current work p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 powders synthesized by solid-state microwave route were used to fabricating thermally evaporated thin films. The micro-thermoelectric devices were composedof 20-pairs and 10-pairs p-Pb0.925Yb0.075Te:Te and n-Pb0.925Yb0.075Se0.2Te0.8 thin films on glass substrates. Overall size of the thin films thermoelectric generators which consist of 20-pairs and 10-pairs of legs connected by aluminumelectrodes were 23 mm×20 mm and 12 mm×10 mm, respectively. The 20-pairs p–n thermocouples in series device generated output maximum open-circuit voltage of 275.3 mV and a maximum output power up to 54.4 nW at temperature difference ∆T= 162 K, and 109.4 mV and 16.7 nW at ∆T=162 K, for 10-pairs, respectively.

Spin Coating Deposition of c-Oriented Wurtzite Gallium Nitride Thin Film

Spin coating growth and characterisations of c-oriented wurtzite structure gallium nitride (GaN) thin film on silicon (Si) substrate with (100) orientation was reported. The precursor solution consisted of a readily available gallium (III) nitrate hydrate powder, ethanol and diethanolamine as starting material, solvent and surfactant. All the structural and optical results showed that c-oriented wurtzite GaN thin film was deposited on Si (100) substrate. Compared with earlier reported work using sol-gel deposition, significant improvements in the structural quality of the GaN thin film were observed. The FWHM value of the thin film was approximately 2.60°. The framework described here is both an easy in setup and simple method as compared to other method such as MBE, MOCVD, and radio frequency sputtering to produce c-oriented wurtzite structure GaN thin film.

The Fabrication of Ag Islands on AlN/GaN/AlN/Si(111) by Using Thermal Evaporator and Thermal Annealing Methods

In this paper, we studied growth of AlN/GaN/AlN on Si (111) by using plasma assisted molecular beam epitaxy (PA-MBE) system. The structural and optical characteristics of the sample have been investigated by using high resolution X-ray diffraction (HR-XRD), Raman spectroscopy and photoluminescence (PL). PL spectrum of the sample has shown sharp and intense band edge emission of GaN with the absence of yellow emission band, indicating good crystal quality of the sample. The silver (Ag) metal contact was then deposited on the sample followed by thermal treatment at 500°C and 700°C, respectively. Treated sample at 700°C showed good spherical Ag islands on sample compared to the treated sample at 500°C. The effect of Ag islands on the electrical characteristics of sample was also examined by using I-V measurement. The results showed that the treated sample at 700°C has decreased the photo-current of Schottky diode.

Hydrogen Gas Sensing Characterizations Based on Nanocrystalline SnO 2 Thin Films Grown on SiO 2 /Si and Al 2 O 3 Substrates

High-quality nanocrystalline (NC) SnO2 thin films were grown on SiO2/Si and Al2O3 substrates using sol–gel spin coating method. The structural properties, surface morphologies and gas sensing properties of the NC SnO2 were investigated. XRD measurements showed a tetragonal rutile structure and the diffraction peaks for NC SnO2 thin films grown on Al2O3 substrates outperformed those of NC SnO2 films grown on SiO2/Si substrates. The surface morphology of the annealed SnO2 thin films at 500 °C appeared as polycrystalline with uniform nanoparticle distribution. Hydrogen (H2) gas sensing performance of the NC SnO2 was examined for H2 concentrations ranging from 150 ppm to 1000 ppm at different temperatures (room temperature, 75 and 125 °C) for over 50 min. The room temperature sensitivities for H2 gas sensors based on NC SnO2 thin films grown on Al2O3 and SiO2/Si substrates was 2570% and 600%, respectively upon exposure to 1000 ppm of H2 gas. While the sensitivity values at 125 °C increased to 9200% and 1950%, respectively.

Formation and Optical Studies of Porous GaN Thin Films via UV-Assisted Electrochemical Etching Approach

This paper presents the investigation of porous gallium nitride (PGaN) thin films by ultra-violet (UV)-assisted electrochemical etching at various etching durations. The etching process was performed in potassium hydroxide aqueous solution under illumination of 150 W xenon lamp. The surface morphology and cross-section of the PGaN thin films were examined by scanning electron microscopy. Increased etching duration resulted in a more homogeneous pore distribution. Results showed that the etching duration strongly influences the layer characteristic of porous structure. Infrared (IR) and Raman studies were performed to investigate the optical properties of PGaN. IR spectroscopy revealed that the PGaN thin films exhibit distinctive IR spectra as compared to the as-grown GaN thin film. The number of interference fringes in the non-reststrahlen band is correlated to the film thickness of as-grown and PGaN thin films. The Raman measurements clearly reveal two forbidden optical phonon modes observed in all the PGaN thin films. This result indicates the crystal disordering in the films. Additionally, the findings show that the intensity of these forbidden modes becomes stronger with increasing etching duration.

Characteristics of Cuprous Oxide Thin Films Deposited on Glass and Polyethylene Terephthalate Substrates

In this work, cuprous oxide (Cu2O) thin films grown on glass and polyethylene terephthalate (PET) substrates using reactive radio frequency magnetron sputtering system were investigated. Copper target with purity of 99.99% were used while high purity argon-oxygen gases were utilized as sputtering gases. Structural, morphological, and optical properties of the films were investigated by X-ray diffraction (XRD), atomic force microscopy and ultra-violet visible spectrophotometer. From the XRD results, only one single diffraction peak corresponding to cubic Cu2O (111) crystal structure were observed for both substrates. The surface morphologies of the samples were in a form of pillar-like. Root mean square surface roughness for Cu2O on glass and PET substrates were 3.37 nm and 3.20 nm, respectively. The films were highly transparent for wavelength above 600 nm. The Cu2O films have direct band gap values of around 2.56 eV as determined by Taucs method.

Effects of Nitridation Temperatures on Gallium Nitride Thin Films Formed on Silicon Substrates

In this article, GaN thin films were successfully grown on p-type silicon (p-Si) substrates with orientation (100) through spin coating method followed by nitridation in ammonia ambient at various temperatures (750 °C, 850 °C, and 950 °C). The morphology of the GaN thin films were performed by using field-emission scanning electron microscopy. The results showed that the grain size increases with increasing nitridation temperature from 750 °C to 950 °C. Optical analysis of the GaN thin films was performed using Fourier transform infrared spectroscopy. It was confirmed from the results that the reflectance intensity of the transverse optical and longitudinal optical phonon modes of wurtzite GaN increases with increasing nitridation temperature. All the measured results show that nitridation temperature plays a very important role in improving the quality of the GaN thin films. Finally, the results revealed that the 950 °C was the optimal growth nitridation temperature for synthesizing GaN thin film.