Nihan Akin

Microstructural defect properties of InGaN/GaN blue light emitting diode structures

In this paper, we study structural and morphological properties of metal-organic chemical vapour deposition-grown InGaN/GaN light emitting diode (LED) structures with different indium (In) content by means of high-resolution X-ray diffraction, atomic force microscopy (AFM), Fourier transform infrared spectroscopy (FTIR), photoluminescence (PL) and current–voltage characteristic (I–V). We have found out that the tilt and twist angles, lateral and vertical coherence lengths of mosaic blocks, grain size, screw and edge dislocation densities of GaN and InGaN layers, and surface roughness monotonically vary with In content. Mosaic defects obtained due to temperature using reciprocal lattice space map has revealed optimized growth temperature for active InGaN layer of MQW LED. It has been observed in this growth temperature that according to AFM result, LED structure has high crystal dimension, and is rough whereas according to PL and FTIR results, bandgap energy shifted to blue, and energy peak half-width decreased at high values. According to I–V measurements, it was observed that LED reacted against light at optimized temperature. In conclusion, we have seen that InGaN MQW structure’s structural, optical and electrical results supported one another.

Titanium Dioxide Thin Films as Methane Gas Sensors

TiO2 thin film was deposited onto n-Si substrate at 100°C by using a sputtering method, and the film was annealed in air atmosphere at range of 500°C-1000°C. The structural and morphological properties of the all films were investigated by X-ray diffraction and atomic force microscope. The gas sensor with interdigitated platinum electrodes was fabricated with photolithographic techniques using the as-deposited and annealed TiO2 thin films as an active material. The sensitivity of the sensors was determined by altering the conductivity of the sensor material under methane gas with various concentrations at different working temperatures. It was determined that the fabricated sensor using as-deposited TiO2 thin film with 10-nm particle size has high sensitivity and fast response/recovery time. The sensor operated at 50°C had also sensitive to the methane gas and its detection performance increased with temperatures. It was observed that the fabricated sensors exhibited reproducible and stable results.

Influence of substrate temperature on structural and optical properties of RF sputtered ZnMnO thin films

The ZnMnO thin films were deposited on glass substrates by radio frequency magnetron sputtering method. The properties of ZnMnO thin films were investigated by high-resolution x-ray diffractometer (HRXRD),atomic force microscopy (AFM), UV-Vis spectrometer and room temperature photoluminescence (PL), under the influence of substrate temperature. The substrate temperature was varied from 300, 400 and 500°C. With increasing the substrate temperature, the structure of the films changed from cubic to hexagonal. The cubic ZnMnO thin films grown along [210] direction, while the hexagonal ones grown along [002] direction. The changes in surface morphology provided a proof on the structural transition. Also, decrease and increase of optical band gap is associated with cubic or hexagonal structure of the films.