Browsing by Author "Bilgili, A. K."

Now showing 1 - 5 of 5

Open Access
A detailed study on optical properties of InGaN/GaN/Al2O3 multi quantum wells
(Springer, 2019) Bilgili, A. K.; Akpınar, Ö.; Öztürk, M. K.; Özçelik, S.; Suludere, Z.; Özbay, Ekmel
In this study optical properties of InGaN/GaN/Al2O3 multi-quantum well (MQW) structures are investigated in detail. Three samples containing InGaN/GaN/Al2O3 MQWs are grown by using metal organic chemical vapor deposition technique. Sapphire (6H–Al2O3) is used as the substrate. Forbidden energy band gaps (Eg) 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 Eg 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.
Open Access
Investigation of structural, optical and morphological properties of InGaN/GaN structure
(Springer, 2019) Bilgili, A. K.; Akpınar, Ö.; Öztürk, M. K; Başköse, C.; Özçelik, S.; Özbay, Ekmel
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.
Open Access
On the elastic properties of INGAN/GAN LED structures
(Springer, 2019-01) Bilgili, A. K.; Akpınar, Ö.; Öztürk, M. K; Başköse, C.; Özçelik, S.; Özbay, Ekmel
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 (Al2O3) 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.
Open Access
Structural properties of InGaN/GaN/Al2O3 structure from reciprocal space mapping
(Springer, 2018) Bilgili, A. K.; Akpınar, Ö.; Kurtuluş, G.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
By using metal organic chemical vapor deposition technique, InGaN/GaN solar cell (SC) structure is deposited over sapphire (Al2O3) wafer as GaN buffer and GaN epitaxial layers. Structural properties of InGaN/GaN/Al2O3 SC structure is investigated by using high resolution X-ray diffraction technique dependent on In content. By using reciprocal space mapping, reciprocal space data are converted to w-θ data with a software. These w-θ data and full width at half maximum data are used for calculating lattice parameters. When compared with w-θ measurements in literature it is seen that especially a- lattice parameter is found very near to universal value from RSM. It is calculated as 3.2650 nm for sample A (S.A) GaN layer and 3.2570 nm for sample B (S.B) GaN layer on (105) asymmetric plane. Strain and stress calculations are made by using these lattice parameters. Strain and stress are calculated as 0.02363 and 8.6051 GPa for S.A GaN layer respectively. Other results are given in tables in the results and discussion section of this article. Edge, screw and mixed type dislocations are calculated as mosaic defects. All these calculations are made for two samples on (002) symmetric and (105) asymmetric planes. As a result it is seen that measurements by using RSM give more sensitive results. a- lattice parameter calculated with this technique is the best indicator of this result.
Open Access
Swanepoel method for AlInN/AlN HEMTs
(Springer, 2020) Akpınar, Ö.; Bilgili, A. K.; Başköşe, Ü. C.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
In this study, AlInN/AlN high electron mobility transistor (HEMT) structure is grown on c-oriented sapphire substrate using metal organic chemical vapor deposition method. Optical properties of the structure are investigated by photoluminescence (PL) and ultraviolet (UV–Vis.) spectras. According to PL results, direct bandgap of AlN is determined around 2.80 eV. In UV–Vis. spectra it is seen that conduction of AlInN layer starts at 360 nm. Swanepoel envelope method is applied on transmission spectra and some optical properties such as refractive index (n), film thickness (t), absorption coefficient (α), and extinction coefficient (k) are determined. Forbidden energy bandgap is determined again from Tau method and it is compared with the value gained from PL spectra. This study is a rare one that presents optical properties of HEMTs using Swanepoel and Tau methods. In addition to this, it helps estimating how optical properties of HEMTs effect electrical properties.