Browsing by Author "Özçelik, S."

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Open Access
Analysis of the mosaic defects in graded and non graded InxGa1‐xN solar cell structures
(Süleyman Demirel Üniversitesi, 2017) Kars Durukan, İ.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
In this study, graded (A) InxGa1‐xN (10.5 ≤ x ≤ 18.4) and non graded (B) InxGa1‐xN (13.6 ≤ x ≤ 24.9) samples are grown on c‐oriented sapphire substrate using the Metal Organic Chemical Vapour Deposition (MOCVD) technique. The structural, optical and electrical features of the grown InGaN/GaN solar cell structures are analyzed using High Resolution X‐Ray Diffraction (HRXRD), Photoluminescense (PL), Ultraviolet (UV), current density and potential (JV) measurements. According to the HRXRD results; it is determined that the InGaN layer of the graded structure has a lower FWHM (Full width at half maximum) value. From the PL measurements, it is observed that the GaN half‐width peak value of the graded sample is narrower and the InGaN peak width value of the graded sample is larger. From UV measurements, that the graded sample has a greater band range. JV measurements determine that the performance of the graded structure is higher.
Open Access
Analyzing the AlGaN/AlN/GaN heterostructures for HEMT applications
(American Scientific Publishers, 2018-03) K. Durukan, İ.; Akpınar, Ö.; Avar, C.; Gultekin, A.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
In the present work, we have reported two high-electron-mobility transistor structures (HEMTs) with different thick AlN buffer deposited on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). AlN buffer layer has a critical important for the device performance therefore its effect of hererostructures analyzed using mosaic model. AlGaN/AlN/GaN heterostructures were examined by X-ray diffraction (XRD) and Atomic-force microscope (AFM). In order to evaluate the mosaicity of GaN, AlGaN, AlN layers in the structures, mosaic model was also used. These layers of lateral and vertical crystal size, dislocations, tilt and stain are investigated with HR-XRD device by Vegard and William Hall (WH) semi-experimental methods. According to the XRD results; As the buffer layer thickness decreases, the FWHM values of symmetric (002) and asymmetric peaks (105) of epitaxial layers increase. The thicker buffer layer makes the structure more crystalized. According to the AFM results the lower thickness AlN buffer has more frequent pits and hillocks and has more rough. As a result, the 520 nm thick AlN buffer layer showed a better structural performance.
Open Access
Analyzing the InGaN LED structures for white LED applications
(Gazi Üniversitesi, 2017) Durukan, İ. K.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
In this paper, blue-light InGaN/GaN light-emitting diodes were deposited on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) to investigate the properties of blue LEDs with various well thickness having different indium composition. Structural properties of LEDs was studied by high-resolution X-ray diffraction (HRXRD), Photoluminescence (PL) and ultraviole (UV). Our aim is to increase the quality of the LED structure by taking advantage of the mosaic structure calculations. The use of LED in commercial areas has increased. But, there are great difficulties in preventing defects. Lateral and vertical crystal size, dislocations, tilt and twist properties are investigated with HR-XRD device by Vegard and William hall semi-experimental methods. While dislocation value of the first sample is lower than first sample with less indium content ration, stress value of first sample is higher than second sample. In addition, The twist angle of first sample is lower. This shows that while the structure is crystallized, the tension is much greater, which is an interesting result. This is due to the mismatch when the diode is cooled to lower temperatures than the growth temperature.
Open Access
The behavior of the I-V-T characteristics of inhomogeneous (Ni∕Au)-Al0.3Ga0.7N∕AlN∕GaN heterostructures at high temperatures
(EDP Sciences, 2007-09-12) Tekeli, Z.; Altındal, S.; Çakmak, M.; Özçelik, S.; Çalıikan, D.; Özbay, Ekmel
We investigated the behavior of the forward bias current-voltage-temperature (I-V-T) characteristics of inhomogeneous (Ni/Au)-Al0.3Ga0.7N/AlN/GaN heterostructures in the temperature range of 295-415 K. The experimental results show that all forward bias semilogarithmic I-V curves for the different temperatures have a nearly common cross point at a certain bias voltage, even with finite series resistance. At this cross point, the sample current is temperature independent. We also found that the values of series resistance (R-s) that were obtained from Cheung's method are strongly dependent on temperature and the values abnormally increased with increasing temperature. Moreover, the ideality factor (n), zero-bias barrier height (Phi(B0)) obtained from I-V curves, and R-s were found to be strongly temperature dependent and while Phi(B0) increases, n decreases with increasing temperature. Such behavior of Phi(B0) and n is attributed to Schottky barrier inhomogeneities by assuming a Gaussian distribution (GD) of the barrier heights (BHs) at the metal/semiconductor interface. We attempted to draw a Phi(B0) versus q/2kT plot in order to obtain evidence of the GD of BHs, and the values of (Phi) over bar (B0)=1.63 eV and sigma(0)=0.217 V for the mean barrier height and standard deviation at a zero bias, respectively, were obtained from this plot. Therefore, a modified ln(I-0/T-2)-q(2)sigma(2)(0)/2(kT)(2) versus q/kT plot gives Phi(B0) and Richardson constant A(*) as 1.64 eV and 34.25 A/cm(2) K-2, respectively, without using the temperature coefficient of the barrier height. The Richardson constant value of 34.25 A/cm(2) K-2 is very close to the theoretical value of 33.74 A/cm(2) K-2 for undoped Al0,3Ga0,7N. Therefore, it has been concluded that the temperature dependence of the forward I-V characteristics of the (Ni/Au)-Al0.3Ga0.7/AlN/GaN heterostructures can be successfully explained based on the thermionic emission mechanism with the GD of BHs.
Open Access
Buffer effects on the mosaic structure of the HR-GaN grown on 6H-SiC substrate by MOCVD
(Springer New York LLC, 2017) Arslan, E.; Öztürk, M. K.; Tıraş, E.; Tıraş, T.; Özçelik, S.; Özbay, Ekmel
High-resistive GaN (>108 Ω cm) layers have been grown with different buffer structures on 6H-SiC substrate using metalorganic chemical vapor deposition reactor. Different combination of the GaN/AlN super lattice, low temperature AlN, high temperature AlN and AlxGa1−xN (x ≈ 0.67) layers were used in the buffer structures. The growth parameters of the buffer layers were optimized for obtaining a high-resistive GaN epilayer. The mosaic structure parameters, such as lateral and vertical coherence lengths, tilt and twist angle (and heterogeneous strain), and dislocation densities (edge and screw dislocations) of the high-resistive GaN epilayers have been investigated using x-ray diffraction measurements. In addition, the residual stress behaviors in the high-resistive GaN epilayers were determined using both x-ray diffraction and Raman measurements. It was found that the buffer structures between the HR-GaN and SiC substrate have been found to have significant effect on the surface morphology and the mosaic structures parameters. On the other hand, both XRD and Raman results confirmed that there is low residual stress in the high-resistive GaN epilayers grown on different buffer structures.
Open Access
Characterization of AlInN/AlN/GaN heterostructures with different AlN buffer thickness
(Springer New York LLC, 2016) Çörekçi, S.; Dugan, S.; Öztürk, M. K.; Çetin, S. Ş.; Çakmak, M.; Özçelik, S.; Özbay, Ekmel
Two AlInN/AlN/GaN heterostructures with 280-nm- and 400-nm-thick AlN buffer grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD) have been investigated by x-ray diffraction (XRD), atomic force microscopy (AFM), photoluminescence (PL) and Hall-effect measurements. The symmetric (0002) plane with respect to the asymmetric (101 ¯ 2) plane in the 280-nm-thick AlN buffer has a higher crystal quality, as opposed to the 400-nm-thick buffer. The thinner buffer improves the crystallinity of both (0002) and (101 ¯ 2) planes in the GaN layers, it also provides a sizeable reduction in dislocation density of GaN. Furthermore, the lower buffer thickness leads to a good quality surface with an rms roughness of 0.30 nm and a dark spot density of 4.0 × 108 cm−2. The optical and transport properties of the AlInN/AlN/GaN structure with the relatively thin buffer are compatible with the enhancement in its structural quality, as verified by XRD and AFM results.
Open Access
Characterization of an AlN buffer layer and a thick-GaN layer grown on sapphire substrate by MOCVD
(Springer, 2010-10-23) Çörekçi, S.; Öztürk, M. K.; Bengi, A.; Çakmak, M.; Özçelik, S.; Özbay, Ekmel
An AlN buffer layer and a thick-GaN layer for high-electron-mobility transistors (HEMTs) were grown on sapphire substrate by metal-organic chemical vapor deposition (MOCVD). The structural and morphological properties of the layers were investigated by high resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) techniques. The optical quality of the thick-GaN layer was also evaluated in detail by a photoluminescence (PL) measurement. It was found that the AlN buffer layer possesses high crystal quality and an atomically flat surface with a root-mean-square (rms) roughness of 0.16 nm. The screw-and edge-type dislocation densities of the thick-GaN layer were determined as 5.4 9 107 and 5.0 9 109 cm-2 by means of the mosaic crystal model, respectively. It was observed that the GaN layer has a smooth surface with an rms of 0.84 nm. Furthermore, the dark spot density of the GaN surface was estimated as 6.5 9 108 cm-2 over a scan area of 4 μm2. © Springer Science+Business Media, LLC 2010.
Open Access
Comparison of the transport properties of high quality AlGaN/AlN/GaN and AllnN/AlN/GaN two-dimensional electron gas heterostructures
(AIP Publishing LLC, 2009-01-07) Tülek, R.; Ilgaz, A.; Gökden, S.; Teke, A.; Öztürk, M. K.; Kasap, M.; Özçelik, S.; Arslan, E.; Özbay, Ekmel
The transport properties of high mobility AlGaN/AlN/GaN and high sheet electron density AlInN/AlN/GaN two-dimensional electron gas (2DEG) heterostructures were studied. The samples were grown by metal-organic chemical vapor deposition on c-plane sapphire substrates. The room temperature electron mobility was measured as 1700 cm(2)/V s along with 8.44 X 10(12) cm(-2) electron density, which resulted in a two-dimensional sheet resistance of 435 Omega/square for the Al(0.2)Ga(0.8)N/AlN/GaN heterostructure. The sample designed with an Al(0.88)In(0.12)N barrier exhibited very high sheet electron density of 4.23 X 10(13) cm(-2) with a corresponding electron mobility of 812 cm(2)/V s at room temperature. A record two-dimensional sheet resistance of 182 Omega/square was obtained in the respective sample. In order to understand the observed transport properties, various scattering mechanisms such as acoustic and optical phonons, interface roughness, and alloy disordering were included in the theoretical model that was applied to the temperature dependent mobility data. It was found that the interface roughness scattering in turn reduces the room temperature mobility of the Al(0.88)In(0.12)N/AlN/GaN heterostructure. The observed high 2DEG density was attributed to the larger polarization fields that exist in the sample with an Al0.88In0.12N barrier layer. From these analyses, it can be argued that the AlInN/AlN/GaN high electron mobility transistors (HEMTs), after further optimization of the growth and design parameters, could show better transistor performance compared to AlGaN/AlN/GaN based HEMTs. c 2009 American Institute of Physics.
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
Discolation-governed current-transport mechanism in (Ni/Au)-AlGaN/AIN/GaN heterostructures
(A I P Publishing LLC, 2009-01-22) Arslan, E.; Altındal, S.; Özçelik, S.; Özbay, Ekmel
The current-transport mechanisms in (Ni/Au)-Al(0,22)Ga(0,78)N/AlN/GaN heterostructures were studied by using temperature dependent forward-bias current-voltage (I-V) characteristics in the temperature range of 80-410 K. In order to determine the current mechanisms for (Ni/Au)-Al(0,22)Ga(0,78)N/AlN/GaN heterostructures, we fitted the experimental I-V data to the analytical expressions given for the current-transport mechanisms in a wide range of applied biases and at different temperatures. The contributions of thermionic-emission, generation-recombination, tunneling, leakage currents that are caused by inhomogeneities, and defects at the metal-semiconductor interface current mechanisms were all taken into account. The best fitting results were obtained for the tunneling current mechanism. On the other hand, we did not observe sufficient agreement between the experimental data and the other current mechanisms. The temperature dependencies of the tunneling saturation current (I(t)) and tunneling parameters (E(0)) were obtained from fitting results. We observed a weak temperature dependence of the saturation current and the absence of the temperature dependence of the tunneling parameters in this temperature range. The results indicate that in the temperature range of 80-410 K, the mechanism of charge transport in the (Ni/Au)-Al(0.22)Ga(0.78)N/AlN/GaN heterostructure is performed by tunneling among those dislocations intersecting the space charge region. The dislocation density (D) that was calculated from the I-V characteristics, according to a model of tunneling along the dislocation line, gives the value of 0.24x10(7) cm(-2). This value is close in magnitude to the dislocation density that was obtained from the x-ray diffraction measurements.
Open Access
The effect of strain relaxation on electron transport in undoped Al0.25Ga0.75N/GaN heterostructures
(Elsevier BV * North-Holland, 2007-11-01) Lişesivdin, S. B.; Yıldız, A.; Acar, S.; Kasap, M.; Özçelik, S.; Özbay, Ekmel
The two-dimensional electron gas (2DEG) transport properties of two-step growth undoped Al0.25Ga0.75N/GaN heterostructures with semi-insulating buffer, grown by MOCVD, were investigated in a temperature range of 20–350 K. Using the quantitative mobility spectrum analysis (QMSA) method, it was shown that significant parallel conduction does not occur in worked structures. In-plain growth axis strains are calculated using the total polarization-induced charge density taken as the sheet carrier density measured from the Hall effect. It was found that the calculated strain values are in good agreement with those reported. Influences of the two-step growth parameters such as growth ramp time, the annealing temperature of the GaN nucleation layer on the mobility, and density of the 2DEG are also discussed.
Open Access
Effects of high-temperature AIN buffer on the microstructure of AlGaN/GaN HEMTs
(Pleiades Publishing, 2013) Çörekçi, S.; Öztürk, M. K.; Yu, H.; Çakmak, M.; Özçelik, S.; Özbay, Ekmel
Effects on AlGaN/GaN high-electron-mobility transistor structure of a high-temperature AlN buffer on sapphire substrate have been studied by high-resolution x-ray diffraction and atomic force microscopy techniques. The buffer improves the microstructural quality of GaN epilayer and reduces approximately one order of magnitude the edge-type threading dislocation density. As expected, the buffer also leads an atomically flat surface with a low root-mean-square of 0.25 nm and a step termination density in the range of 108 cm-2. Due to the high-temperature buffer layer, no change on the strain character of the GaN and AlGaN epitaxial layers has been observed. Both epilayers exhibit compressive strain in parallel to the growth direction and tensile strain in perpendicular to the growth direction. However, an high-temperature AlN buffer layer on sapphire substrate in the HEMT structure reduces the tensile stress in the AlGaN layer.
Open Access
Effects of the AlN nucleation layer thickness on the crystal structures of an AlN epilayer grown on the 6H-SiC substrate
(Taylor & Francis, 2019-04-08) Arslan, Engin; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
The influence of the LT-AlN(NL) growth times on the mosaic structure parameters of the AlN layer grown on the LT-AlN(NL)/6H-SiC structures as well as the dislocation densities and the strain behaviours in the AlN epilayers has been investigated using XRD measurements. The growth times of the LT-AlN(NL) were changed to 0, 60, 120, 180, and 240 s. We observed that the mosaic structure parameters of the AlN epilayers were slightly affected by the LT-AlN(NL) growth times. However, the dislocation densities in the AlN layer are affected by the growth times of the LT-AlN(NL) layer. The highest edge dislocation density (5.48 × 1010 ± 2.3 × 109 cm−2) was measured for the sample in which 120 s grown LT-AlN(NL) was used. On the other hand, highest screw type dislocation density (1.21 × 1010 ± 1.7 × 109 cm−2) measured in the sample E that contains 240 s growth LT-AlN(NL). The strain calculation results show that the samples without LT-AlN(NL) suffered maximum compressive in-plane strain (−10.9 × 10−3 ± 1.8 × 10−4), which can be suppressed by increasing the LT-AlN(NL) growth times. The out-of-plane strain also has a compressive character and its values increase with LT-AlN(NL) growth times between 60 and 180 s. Same out-of-plane strain values were measured for the LT-AlN(NL) growth times of 180 and 240 s. Furthermore, the form of the biaxial stress in the AlN epilayer changed from compressive to tensile when the LT-AlN(NL) growth times were greater than 120 s.
Open Access
The electrical, optical, and structural properties of GaN epitaxial layers grown on Si(111) substrate with SiNx interlayers
(ELSEVIER, 2009-10-12) Arslan, E.; Duygulu, Ö.; Kaya, A. A.; Teke, A.; Özçelik, S.; Özbay, Ekmel
The effect of the in situ substrate nitridation time on the electrical, structural and optical properties of GaN films grown on Si(111) substrates by metal organic chemical vapor deposition (MOCVD) was investigated. A thin buffer layer of silicon nitride (SiNx) with various thicknesses was achieved through the nitridation of the substrate at different nitridation times ranging from 0 to 660 s. The surface roughness of the GaN film, which was grown on the Si substrate 10 s, exhibited a root mean square (RMS) value of 1.12 nm for the surface roughness. However, further increments in the nitridation times in turn cause increments in the surface roughness in the GaN layers. The number of threading dislocation (TD) was counted from plan-view TEM (Transmission Electron Microscopy) images. The determined density of these threading dislocations was of the order of 9×109 cm-2. The sheet resistances of the GaN layers were measured. The average sheet resistance significantly increases from 2867 Ω sq-1 for sample A (without nitridation) to 8124 Ω sq-1 for sample F (with 660 s nitridation). The photoluminescence (PL) measurements of the samples nitridated at various nitridation times were done at a temperature range of 10-300 K. A strong band edge PL emission line, which was centered at approx. 3.453 eV along with its phonon replicas which was separated by approx. 92 meV in successive orders, was observed at 10 K. The full width at half maximum (FWHM) of this peak is approx. 14 meV, which indicates the reasonable optical quality of the GaN epilayers grown on Si substrate. At room temperature, the peak position and FWHM of this emission became 3.396 eV and 58 meV, respectively.
Open Access
Energy relaxations of hot electrons in AlGaN/AlN/GaN heterostructures grown by MOCVD on sapphire and 6H-SiC substrates
(E D P Sciences, 2011-08-18) Ilgaz, A.; Gökden, S.; Tülek, R.; Teke, A.; Özçelik, S.; Özbay, Ekmel
In this work, we investigated the hot-electron dynamics of AlGaN/GaN HEMT structures grown by MOCVD on sapphire and SiC substrates at 80 K. High-speed current-voltage measurements and Hall measurements over the temperature range 27-300 K were used to study hot-electron dynamics. At low fields, drift velocity increases linearly, but deviates from the linearity toward high electric fields. Drift velocities are deduced as approximately 6.55 × 10 6 and 6.60 × 106 cm/s at an electric field of around E ∼ 25 kV/cm for samples grown on sapphire and SiC, respectively. To obtain the electron temperature as a function of the applied electric field and power loss as a function of the electron temperature, we used the so-called mobility comparison method with power balance equations. Although their low field carrier transport properties are similar as observed from Hall measurements, hot carrier energy dissipation differs for samples grown on sapphire and SiC substrates. We found that LO-phonon lifetimes are 0.50 ps and 0.32 ps for sapphire and SiC substrates, respectively. A long hot-phonon lifetime results in large non- equilibrium hot phonons. Non-equilibrium hot phonons slow energy relaxation and increase the momentum relaxation. The effective energy relaxation times at high fields are 24 and 65 ps for samples grown on sapphire and SiC substrates, respectively. They increase as the electron temperature decreases.
Open Access
Examination of the temperature related structural defects of InGaN/GaN solar cells
(Academic Press, 2015) Durukan, İ. K.; Bayal, Ö.; Kurtuluş, G.; Baş, Y.; Gültekin, A.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Özçelik, S.; Özbay, Ekmel
In this study the effects of the annealing temperature on the InGaN/GaN solar cells with different In-contents grown on sapphire substrate by the Metal Organic Chemical Vapor Deposition (MOCVD) are analyzed by High Resolution X-ray Diffraction (HRXRD) and an Atomic Force Microscope (AFM). The plane angles, mosaic crystal sizes, mixed stress, dislocation intensities of the structure of the GaN and InGaN layers are determined. According to the test results, there are no general characteristic trends observed due to temperature at both structures. There are fluctuating failures determined at both structures as of 350 °C. The defect density increased on the GaN layer starting from 350 °C and reaching above 400 °C. A similar trend is observed on the InGaN layer, too.
Open Access
Femtosecond response of J aggregates adsorbed onto silver colloid surfaces
(2003) Yaǧlioǧlu G.; Dorsinville, R.; Özçelik, S.
The observation of stimulated emission from J aggregates adsorbed onto silver colloid surfaces using femtosecond excitation was reported. The stimulated emission was inferred from the excitation intensity and wavelength dependence of the emission band. The stimulated emission originated from the amplification of the one-exciton state emission by an induced transition from the two-exciton state to the one-exciton state.
Open Access
InGaN/GaN LED yapıların mozaik yapı analizi
(Osman Sağdıç, 2018) Durukan, İ. K.; Öztürk, M. K.; Özçelik, S.; Özbay, Ekmel
Bu çalışmada, MOCVD yöntemi ile üretilen InGaN/GaN ışık yayan diyot (LED) yapılarının mozaik yapıları analiz edildi. Safir alttaş üzerine biriktirilen, farklı In kompozisyonuna sahip InGaN/GaN bariyer tabakasının mozaik yapı üzerine etkisi Yüksek Çözünürlü X Işını Kırınımı (HR-XRD) yöntemi ile karakterize edildi. Amacımız mozaik yapı hesaplarından yararlanarak LED yapısının kalitesini arttırmaktır. Günümüzde LED' lerin geniş bir kullanım alanına sahip olmasından dolayı sektörde büyük bir pazar payı bulunmaktadır. Özellikle InGaN gibi, GaN bazlı LED' ler arsenik bazlı LED' lerden daha yüksek güç, sıcaklık ve frekans aralıklarında çalışabilirler. Ancak GaN tabanlı LED' ler hala yüksek kusur yoğunluklarına sahiptir. Bu nedenle çalışmalarımızda mozaik yapı analizi yapıldı. Hesaplamalarımızda Vegard ve William Hall yarı deneysel metotları kullanıldı. Kompozisyonun, kenar ve vida türü kusurların azalmasına yol açan önemli bir faktör olduğunu söyleyebiliriz.
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
Microstructural analysis with graded and non-graded indium in InGaN solar cell
(American Scientific Publishers, 2017) Durukan, I. K.; Öztürk, M. K.; Çörekçi, S.; Tamer, M.; Baş, Y.; Özçelik, S.; Özbay, Ekmel
In this study are graded and non graded InGaN/GaN samples grown on c-oriented sapphire substrate using the Metal Organic Chemical Vapour Deposition (MOCVD) technique. The structural and morphological properties of the grown InGaN/GaN solar cell structures are analyzed using High Resolution X-ray Diffraction (HRXRD), atomic force microscopy (AFM). Each structures c and a lattice parameters strain, biaxial strain, hydrostatic strain, stress, lattice relax, tilt angle, mosaic crystal size, dislocation densities of GaN and InGaN layers are determined by XRD measurements. In accordance with these calculations, the effect of graded structure on the defects, are discussed. As a dramatic result; although values of full width at half maximum (FWHM) are broad, a considerable decrease at dislocations is noticed. The AFM observations have revealed that the two dimensional growth of the graded sample is more significant and its roughness value is lower. JV measurements shown that the performance of the graded structure is higher. It is determined that all test results are consistent with each other.