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AlxGa1−xN/GaN/AlN heterostructures on silicon (Si) substrate was developed by nitrogen plasma-assisted molecular beam epitaxy (MBE) and their properties were investigated by scanning electron microscopy (SEM), electron dispersive X-ray (EDX), atomic force microscopy (AFM), high resolution X-ray diffraction (XRD), Raman spectroscopy and Hall effect measurements. High purity gallium (7N) and aluminum (6N5) were used in the Knudsen cells. High purity nitrogen with 7N purity was supplied to radio frequency (RF) source to generate reactive nitrogen species. The nitrogen pressure and a discharge power were kept at 1.5×10−5 Torr and 300 W, respectively. From SEM measurements, the surface morphology of samples presented 2- and 3-dimensional growth modes. The EDX measurements showed that there were no foreign elements in the grown samples. The HR-XRD measurement has confirmed that the AlxGa1−xN/GaN/AlN heterostructures samples were epitaxially grown on Si substrate. All the dominant E2 phonon modes were found in Raman spectra results. Lastly, AlxGa1−xN/GaN/AlN heterostructures based metal–semiconductor–metal (MSM) UV photodetectors were fabricated and the electrical characteristics of the devices were investigated by using current–voltage (I–V) and photo-conductivity measurements. The devices presented good I–V and photoconductivity characteristics.

In this study, thermoelectric materials based on p-type Bi2Te3 and dispersed with x compositions of selenium (Se) (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in Bi2Se3xTe3(1−x) ingots were synthesized using a standard solid-state microwave method. The crystalline structures of the polycrystalline powders were examined by X-ray diffraction (XRD), which showed the formation of a rhombohedral structure. The surface morphology for the samples showed that the Se alloying is an effective approach for crystalline refinement, which has been characterized by scanning electron microscopy (SEM). The electrical transport properties of the samples were measured from room temperature up to 500 K. The results indicate that the selenium substitution effectively adjusts the carrier concentration allowing an optimum value of 1.25×1020 cm−3. Ascribing to the increased Seebeck coefficient for the sample with x=0.2 (176.3 μV/K), the maximum power factor is 2.85 mW/mK2 at 403 K.

In this research, hexagonal wurtzite structure gallium nitride (GaN) thin film was grown on silicon (Si) substrate by using spin coating deposition method. Simple ethanol-based precursor with the addition of diethanolamine solution was used. High resolution X-ray diffraction results revealed that wurtzite structure GaN thin film with (002) preferred orientation was deposited on Si substrate. Flied-emission scanning electron microscopy and atomic force microscopy results showed that crack free GaN thin film with uniform and dense grains of GaN was formed. Finally, lattice vibrational characterization by p-polarized infrared reflectance technique revealed a strong reststrahlen feature of crystalline wurtzite GaN, and the transverse and longitudinal phonon modes of wurtzite GaN were clearly identified.

The growth and characterization of pn-junction photodiode based on GaN grown on Si (111) by RF-plasma assisted molecular beam epitaxy (MBE) are described. The structural and optical properties of samples were studied by HR-XRD and Fourier FTIR spectroscopy, respectively. For IR reflectance analysis, GaN-like and AlN-like E2 TO optical modes have been detected. By using the thermal evaporator, Ni/Ag and Al contacts were evaporated at the front and back of samples. The application of thermal annealing treatment in oxygen ambient has been shown to significantly reduce the dark current of GaN pn-junction photodiode. The electrical characteristics of all samples were conducted using Keithley's I–V measurement system. Under 460-nm wavelength, at bias voltages of 0.5, 1, and 2 V, the photocurrents rise and decay times were investigated.

In this study p-Pb 0.925 Yb 0.075 Te:Te and n-Pb 0.94 Yb 0.06 Te powders synthesized by solid-state microwave technique were used to fabricate thermally evaporated thin films. The nanostructure and composition of the films were studied using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and energy dispersive X-ray spectroscopy (EDX). Electrical characterizations of the as-deposited films in terms of the Seebeck coefficient and electrical conductivity and power factor were conducted at a range of 298 K to 523 K. The microthermoelectric devices were composed of 20-pair and 10-pair p-Pb 0.925 Yb 0.075 Te:Te and n-Pb 0.94 Yb 0.06 Te thin films on glass substrates. The dimensions of the thin-film thermoelectric generators, which consisted of 20-pair and 10-pair legs connected by aluminum electrodes, were 23 mm×20 mm and 12 mm×10 mm, respectively. The 20-pair p–n thermocouples in series generated a maximum open-circuit voltage output ( V oc ) of 0.581 V and a maximum output power of 25.87×10 −8 W at a temperature difference Δ T =164 K, whereas the 10-pair p–n thermocouples generated 0.311 V and 13.71×10 −8 W maximum V oc and maximum output power, respectively, at Δ T =164 K.

This study reports on the fabrication of a chalcogen-based thermoelectric power generation (TEG) device using p-type Bi 0.4 Sb 1.6 Se 2.4 Te 0.6 and n-type Bi 2 Se 0.6 Te 2.4 legs. Electrical power generation characteristics were monitored by changing both the temperature conditions and the number of p–n couples required to generate maximum power. The significance of the resistances including the internal resistance and contact resistance between legs and electrodes, are discussed. The maximum output power obtained with the 18 p–n couples device was 273.2 mW under the thermal condition of T H =523 K hot-side temperature and Δ T =184 K temperature difference.

In this research, we used an inexpensive method to fabricate highly crystalline gallium nitride (GaN) nanowires (NWs) on porous GaN (PGaN) on a Si (1 1 1) wafer by thermal evaporation using commercial GaN powder using a combination of argon and nitrogen gas atmosphere without any catalyst. Microstructural studies using scanning electron microscopy and transmission electron microscope measurements revealed the role of porosity in the nucleation and alignment of the GaN NWs. The GaN NWs have diameters of 30–45 nm and lengths of around 1 μm. Further structural and optical characterizations were performed using high resolution X-ray diffraction, energy-dispersive X-ray spectroscopy, and photoluminescence spectroscopy. Results indicate that the NWs are of a single-crystal hexagonal GaN and have the growth direction of [0 0 0 1].

We described the fabrication of porous ZnO using the electrochemical etching method. ZnO thin films deposited by radiofrequency sputtering were etched electrochemically using 10 wt% KOH solution as an etching medium to obtain porous ZnO surface structure. A constant voltage of 15 V was applied to enhance the etching process. The etched samples were then characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and photoluminescence (PL) spectroscopy to examine their structural and optical properties. XRD spectra showed that by performing the electrochemical etching process, porous ZnO could be obtained without severely deteriorating the crystallinity of the samples. Moreover, SEM characterization revealed that hillock-type porous ZnO was fabricated successfully. In addition, the cross-sectional SEM images revealed that there were only minimal changes in the layer thickness after the ZnO had been etched for various lengths of time. This finding shows the dominance of the vertical etching process. Notably, the intensity of PL spectra increased and the PL excitation peak exhibited a red shift trend as the etching time increased. These observations are due to the increase of the surface to volume ratio of the ZnO surface and the strain relaxation along the dislocation and grain boundary.

In this article, thermoelectric (TE) materials based on p-type Sb2Te3 samples and dispersed with x amounts of Bi (x=0.0, 0.2, 0.4, 0.6, 0.8, and 1.0) in the form Bi2xSb2(1−x)Te3 were synthesized via a standard solid-state microwave route. The microstructure of the ingots was characterized by field emission scanning electron microscopy. As-synthesized ingots were formed by the assembly of micro-sheet grains. The phase composition of the powders was characterized by X-ray diffraction, revealing a rhombohedral structure. The influence of variations in Bi content (x) on the TE properties of the resulting alloy was studied in the temperature range of 303 K to 523 K. Increases in x caused a decrease in hole concentration and electrical conductivity and an increase in Seebeck coefficient. A maximum power factor of 4.96 mW/mK2 was obtained at about 373 K for a Bi2xSb2(1−x)Te3 sample with x=0.2.