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The effect of the TiO2 interfacial layer on rectifying junction parameters of Ag/TiO2/n-InP/Au Schottky diodes has been investigated using current-voltage (I-V) measurements in the temperature range of 120-420 K with steps of 20 K. The barrier height is found to be 0.19 eV and 0.68 eV from current-voltage characteristics at 120 K and 420 K, respectively. At 120 K and 420 K, the ideality factor is found to be 3.52 and 1.01 for the Ag/TiO2/n-InP/Au Schottky barrier diode, respectively. These results are gained by the thermionic emission theory at room temperature. Values of series resistances gained from the Cheung-Cheung method are compared with results gained from a modified Norde method. These experimental results indicate that series resistance decreases with an increase in temperature. The current-voltage (I-V) measurements showed that the diode with the TiO2 interfacial layer gave a double Gaussian property in the examined temperature range. The Richardson constant is also calculated from a modified Richardson plot and is found to be very compatible with the theoretical value. Interface state density is also examined by using I-V characteristics.

In this study optical properties of InGaN/GaN/Al 2 O 3 multi-quantum well (MQW) structures are investigated in detail. Three samples containing InGaN/GaN/Al 2 O 3 MQWs are grown by using metal organic chemical vapor deposition technique. Sapphire (6H-Al 2 O 3 ) is used as the substrate. Forbidden energy band gaps (E g ) of these three samples are determined from photoluminescence and absorption spectra. Results gained from these two spectra are compared with each other. It is found that E g values are between 2 and 3 eV. For determining refraction index, absorption coefficients, extinction coefficients and thickness of the films a rare method called Swanepoel envelope method is used. It is seen that results gained from this method are consistent with those in literature.

In this study, InGaN/GaN structure is investigated in the temperature range of 300-500 °C with steps of 50 °C. InGaN/ GaN multi-quantum well structure is deposited on c-orientated sapphire wafer by metal organic chemical vapour deposition method. All the parameters except for temperature kept constant during growth period. InGaN/GaN structures with different In content are investigated by XRD technique. Their structural, optical and morphological characteristics are determined by high resolution X-ray diffraction, Fourier transform spectroscopy (FTIR), photo luminescence (PL), transmission and atomic force microscopy (AFM). According to FTIR and PL spectra's, it is noticed that band gap values coincide with blue region in the electromagnetic spectrum. As a result of transmission measurements it is seen that light is completely absorbed by the sample at approximately 390 nm. Using XRD technique, dislocation densities and strain are calculated. Full width at half maximum of the XRD peak values gained from X-ray diffraction are used in an alternative method called Williamson-Hall (W-H). Using W-H method, lateral and vertical crystal lengths and tilt angles are determined. Surface roughness parameters are investigated by AFM. Different properties of GaN and InGaN layers are compared as dependent on increasing temperature. According to AFM images it is seen that these structures have high surface roughness and large crystal size. All the results yielded from the mentioned methods are in good agreement with the previous works done by different authors.

In this study, three InGaN/GaN light-emitting diode (LED) structures with five periods are investigated grown by metal organic chemical vapor deposition (MOCVD) technique. During growth of these three samples, active layer growth temperatures are adjusted as 650, 667 and 700 °C. These structures are grown on sapphire (Al 2 O 3 ) wafer as InGaN/GaN multiquantum wells (MQWs) between n-GaN and p-AlGaN + GaN contact layers. During growth, pressure and flux ratio of all sources are kept constant for all samples. Only temperature of InGaN active layer is changed. These structures are analyzed with high-resolution X-ray diffraction (HR-XRD) technique. Their surface morphologies are investigated with atomic force microscopy (AFM). Reciprocal space mapping (RSM) is made different from classical HR-XRD analyses. Using this method, mixed peaks belonging to InGaN, AlGaN and GaN layers are seen more clearly and their full width at half maximum (FWHM) values is determined with better accuracy. With FWHM gained from RSM and Williamson-Hall (W-H) method based on universal elastic coefficients of the material, particle size D (nm), uniform stress σ (GPa), strain ε and anisotropic energy density u (kJ m −3 ) parameters for the samples are calculated. The results are compared with literature. On the other hand, to have an idea about the accuracy of the results AFM images are examined. Parameters calculated showed differences but it is seen that the largest particle size is gained for GaN and the smallest is gained for AlGaN. For all parameters, it is seen that they increase for GaN layer and decrease for AlGaN layer with increasing temperature. For InGaN layer parameters, they showed both increasing and decreasing or decreasing and increasing behavior harmonically with an increase in temperature. Results showed that they are compatible with literature. Results gained from Scherrer and W-H are very near to each other.