Nanoteknoloji Mühendisliği Bölümü Makale Koleksiyonu

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https://hdl.handle.net/20.500.12418/641

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Effect of structural parameters and applied external fields on the third harmonic generation coefficient of AlGaAs/GaAs three-step quantum well
(Springer, 2024) Dakhlaoui, H.
This presented work includes the first in-depth theoretical investigation of the third harmonic generation (THG) coefficients of the AlGaAs/GaAs three-step quantum well. We explore how these optical properties evolve when influenced by tunable structural parameters and various external fields, including electric, magnetic, and non-resonant intense laser fields. Firstly, we obtained the subband energy eigenvalues and eigenfunctions of the structure using the diagonalization method within the framework of the effective mass and envelope function approach. Then, we calculated the THG coefficients of the structure using the compact density matrix approximation. The obtained numerical results demonstrate that, within a certain range of structural parameter adjustments and applied external field changes, significant shifts (red or blue) occur in the resonance peak of the THG coefficient. These changes elegantly reflect the practical implications of the presented study. Finally, we discuss the optimality of the structure for a certain amount of applied external fields, which can be crucial for pre-experimental studies applications and the design of optoelectronic devices.
Generation of coherent XUV radiation at different interaction lengths using the ultrashort laser system
(World Scientific Publishing Co, 2024) Sayrac, M.
Generation of short wavelengths is obtained using the gas cells having di®erent lengths. A Ti: sapphire laser system at 1 kHz or 10 Hz repetition rate is used to produce high harmonic generation (HHG). The gas cell producing optimum harmonic spectrum is determined using the 1 kHz laser system. The optimum harmonic signal is obtained under the phase-matched condition. The total harmonic yield is increased by adjusting argon gas pressure in the di®erent gas cell lengths (length of the interaction mediums). Harmonics up to the 27th order are obtained. The 1D model is used for the calculation of harmonic yield at di®erent interaction lengths. The high-power laser system at the 10 Hz repetition rate is used to generate high-order harmonics. The harmonic orders are extended to the 35th harmonic in argon gas. A harmonic spectrum in H2 gas is generated using di®erent pump laser power. The power dependence of the harmonic signal from H2 gas is obtained. The variation of the harmonic spectrum for the di®erent cell parameters is explained as a constructive or destructive buildup of generated harmonics while they propagate through the gas cell.
Hydrostatic pressure and temperature effects on nonlinear optical properties in harmonic-Gaussian asymmetric double quantum wells
(IOP Publishing, 2024) Sayrac, M.; Dakhlaoui, H; Mora-Ramos, M. E.; Ungan, F.
The paper examines the linear and non-linear optical characteristics of an electron in harmonic Gaussian asymmetrical double quantum wells, taking into account thermodynamic variables such as temperature and hydrostatic pressure. Numerical calculations by considering the effective mass and parabolic band approximation are performed. The electron contained within an asymmetric double well generated by the sum of a parabolic and Gaussian potential has its eigenvalues and eigenfunctions determined using the diagonalization approach. For nonlinear optical coefficients, the density matrix expansion is used. Wavefunctions and energy levels vary as an effect of the applied fields. In harmonic Gaussian asymmetrical double quantum wells, the total optical absorption coefficient (TOAC), the relative refractive index changes (RRIC), and second harmonic generation (SHG) have all been theoretically investigated. The magnitude and position of the resonant peaks are significantly influenced by the hydrostatic pressure and temperature effects. With controllable coupling and externally applied hydrostatic pressure and temperature, the potential model presented in this study can be used to simulate and manipulate the optical and electronic properties of the asymmetric double-quantum heterostructures, such as double quantum dots and wells.
Optimized synthesis and characterization of La(OH)3 and LaB6 nanostructures for enhanced NIR optical filters
(IOP Publishing, 2024) Bulbul, B. G.; Toprak, B. C.; Sayrac, M.; Ozen, Y.; Ozcelik, S
The present study describes a method for synthesizing nanostructured La(OH)3 and LaB6 materials with efficient field emission properties using the spin coating technique. The study was motivated by the significant demand for the optical properties of LaB6 with efficient field emission properties using the spin coating technique in the near-infrared (NIR) region. The optimization of the LaB6 synthesis process for economic and reproducible results is highlighted, showcasing a systematic approach starting from La(OH)3 formation through chemical mixing and high-temperature heating, followed by boron incorporation. The systematic methodology includes forming La(OH)3 through chemical mixing and high-temperature heating, followed by combining it with boron to achieve the LaB6 structure. Characterization methods such as XRD, FTIR, SEM, AFM, and SIMS validated the successful synthesis and uniformity of the materials. Optical analyses showed increased visible transmittance and reduced infrared transmittance for the LaB6 thin film. Optical analyses showed increased visible transmittance and decreased infrared transmittance in the 110nmthick LaB6 film, with an absorption valley at 1000 nm. SEM images revealed microstructural features andAFManalysis indicated a homogeneous distribution of La and B atoms with anRMS value of 0.87 nm. SIMS analysis confirmed uniform atomic distribution throughout the film thickness. The optimized recipes contribute to the efficiency and controllability of the synthesis process. The presented results provide valuable insights into material synthesis methodologies and serve as a crucial reference for utilizing LaB6 materials in infrared devices.
Microencapsulated propolis in chewing gum production
(2023) Gölge, Evren; Bostancı, Emre
Propolis is a resin with high antibacterial and antioxidant properties that honey bees (Apis mellifera L.) gather and then harmonize through their metabolic secretions. Propolis is beneficial to dental health because it contains antibacterial activity against the Streptococcus mutans, which causes tooth decay. The aim of this study is to use microencapculated propolis extract (MPE) in chewing gum formulation for the first time, in order to protect propolis from environmental effects during production and to ensure controlled release in mouth. Spray drying method was applied where maltodextrin acted as coating material. The particle structure of MPE was investigated by scanning electron microscope. The encapsulation efficiency was determined as 62.19%. The hygroscopicity and moisture content of the MPE particles was found as 31.50% and 7.98% respectively. The DPPH scavenging ability, total flavonoid and total phenolic content of the MPE appeared lower than propolis extract. The total flavonoid content of MPE was calculated as 29.06 mg/kg and total phenolic content as 89.17 mg/kg. In vitro antimicrobial activity against Streptococcus mutans of 9% MPE containing gum samples was measured highest with 4.20 mm zone diameter. Hunter b* value increased with increasing MPE concentration. The final MPE incorporated chewing gum appear to be highly functional.
Rheology and sensory properties of microencapsulated propolis-enriched stirred-type yogurt
(Codon Publishing Co., 2023) Gölge, Evren; Taşdemir, Yasemin
In this study, the rheological, sensory and syneristic properties of yogurt enriched with 0.5%, 1% and 2% microencapsulated propolis (MP) was investigated. The viscosity measurements of stir-type yoghurt were performed with Brookfield DV-II viscometer. Shear rate varying between 0.02 s-1 and 100 s-1 flow models was obtained for rising and descending curves with the Rheocalc v3.3 software. Three flow models—Power Law, Herschel–Bulkley, and Casson models—were evaluated. All samples used in this analysis showed non-Newtonian and pseudoplastic properties. During the 21-day storage period, the Power Law flow model was optimal.
Production of phenylalanine-reduced soymilk for phenylketonuria patients
(Codon Publishing Co., 2023) Gölge, Evren; Taşdemir, Yasemin
Phenylketonuria (PKU) is a hereditary disease caused by the deficiency of phenylalanine (Phe) hydroxylase enzyme or its cofactor tetrahydrobiopterin. Treatment involves a Phe-restricted diet, although food options are limited. Soymilk, derived from soybeans, is a functional food with nutritional benefits. In this study, soymilk was produced and hydrolyzed with protease of Aspergillus oryzae and papain, and then activated carbon was used to remove Phe for PKU patients. The second-derivative spectrophotometry method was used to determine Phe content in soymilk. The results showed no significant difference in dry matter, fat, and crude fiber between soymilk and Phe-extracted soymilk with respect to the control group (P < 0.05). Soymilk’s protein content was calculated as 2.74% (w/w) and that of Phe-reduced soymilk as 1.94% (w/w). Similarly, consecutive Phe content was 40.53 mg/L and 5.09 mg/L. After hydrolization, the calculated Phe removal rate was 87.44% (w/w), and the protein content was reduced by 29.19% (w/w). The study demonstrates that Phe-reduced soymilk is suitable for PKU patients, thus reducing the need for imported products and offering new market opportunities.
Effect of Si-doped and undoped inter-layer transition time on the strain-compensated InGaAs/InAlAs QCL active region grown with MOVPE
(15.01.2023) Pertikel İzel; Demir İlkay
In this study, we report the effect of the combination of Si-doped and undoped inter-layer transition time in the strain compensated In 0.67 Ga 0.33 As/In 0.36 Al 0.64 As quantum cascade laser (QCL) structure grown on InP substrate by Metal Organic Vapor Phase Epitaxy (MOVPE). In situ reflectance spectroscopy and high resolution X-ray diffraction (HRXRD) technique have been used for the analysis of growth steps and crystalline quality of QCL structures, respectively. In addition, since thickness accuracy is very important for QCLs, two different thickness calculation methods have been used in the Global Fit simulation program for detailed thickness accuracy of structures. As a result, optimum values for thickness accuracy have been obtained as 5 and 10 s between undoped and Si-doped layers, respectively, as verified by the two methods.
InGaAs-based Gunn light emitting diode
(14.02.2023) G. Kalyon; S. Mutlu; F. Kuruoglu; I. Pertikel; I. Demir; A. Erol
We report an n-type In0.53Ga0.47As based Gunn light emitting diode operated at around 1.6 μm. The device structure comprises of an n-type In0.53Ga0.47As epilayer with a thickness of 5 μm grown by Metal Organic Vapour Phase Epitaxy (MOVPE) on a semi-insulating InP substrate and fabricated in a planar architecture with a stepped structure at anode side to suppress the destructive effect of high built-in electric field in propagating Gunn domain. Gunn diode is operated under pulsed voltage with a pulse width of 60 ns and pulse duration of 4.5 ns to keep the duty cycle as low as 0.0013%. The Gunn oscillations with an 1 ns period are observed at around 4.1 kV/ cm, which corresponds to the electric field threshold of Negative Differential Resistance (NDR). The light emission at around 1.6 μm also starts at the threshold electric field of the NDR region (E = 4.2 kV/cm) of the current-voltage curve, and the emission intensity increases drastically with increasing applied electric field. The observed light emission at NDR threshold electric field where Gunn oscillations appear on the voltage pulse is attributed to the impact ionisation process occurring in the current domains along the sample, which generates excess carriers to initiate the band-to-band recombination in In0.53Ga0.47As.
Experimental insights toward carrier localization in in-rich InGaAs/InP as candidate for SWIR detection: Microstructural analysis combined with optical investigation
(15.01.2023) Arbia, Marwa Ben; Demir, İlkay; Kaur, Navpreet; Saidi, Faouzi; Zappa, Dario; Comini, Elisabetta; Altuntaş, İsmail; Maaref, Hassen
Hyperspectral imaging has been flourished thanks to the huge investigation of the infrared spectrum from NIR to LWIR bands. The ternary InGaAs has been investigated herein in the context of studying the structural dependences of localization phenomenon by X-ray diffraction (XRD), scanning electron microscopy-energy dispersive X-ray (SEM-EDX), Raman, ultraviolet–visible (UV–vis), and photoluminescence (PL) techniques. Using metal-organic vapor phase epitaxy (MOVPE), we succeed to grow the InGaAs directly on InP substrate at 560 ◦C as an active layer with indium concentration exceeding the “golden” value (53%) to enlarge its cutoff absorption wavelength. X-ray diffraction proved a good crystallinity of the heterostructure with a sharp peak related to the thick substrate and another peak attributed to the thin layer of InGaAs. Moreover, an interfacial layer appeared at the logarithmic scale of XRD patterns and was confirmed by Raman analysis. The SEM-EDX revealed an average indium concentration (62%), almost the growth concentration. However, a cross-section compositional profile over the heterostructure showed an inhomogeneous distribution of the indium. This is predictable from the composition fluctuation in the indium-containing alloys and the volatility (surface segregation) of As (In). On the other side, the optical investigation of InGaAs demonstrated an anomalous behavior of luminescence versus temperature, manifested by the S-shape feature. This trend stems from the potential fluctuation induced by the non-uniform distribution of indium. A numerical simulation was developed based on the localized state ensemble (LSE) model to well-reproduce this anomaly by giving the best fitting parameters and comparing them with those calculated using the semi-empirical models (Vi˜na and P¨assler). The results reported here will help in optimizing the epitaxy design of future InGaAs/InP and further studying its surface morphology and device performance.
Modeling of temperature?dependent photoluminescence of GaN epilayer by artificial neural network
(22.06.2023) ŞenadımTüzemen, Ebru; Yüksek, Ahmet Gürkan; Demir, İlkay; Horoz, Sabit; Altuntaş, İsmail
Artificial neural networks (ANNs) are a type of machine learning model that are designed to mimic the structure and function of biological neurons. They are particularly well-suited for tasks such as image and speech recognition, natural language processing, and prediction tasks. The success of an ANN in modeling a particular dataset depends on factors such as the size and quality of the dataset, the complexity of the model, and the choice of training algorithms. High representation rate of a system in the data set can improve the performance of the ANN model. The study we described is focused on using artificial neural networks (ANNs) to model temperature-dependent photoluminescence (PL) characterization of GaN epilayers grown on patterned sapphire substrates (PSS) using the metalorganic chemical vapor deposition (MOCVD) technique. The ANN model is trained using temperature and wavelength as input parameters and intensity as the output parameter, with the goal of accurately predicting the PL intensity of the GaN epilayer as a function of temperature and wavelength. The model is trained using a large set of experimental data and then tested using data that was not presented to the model during training. The results of the study suggest that ANN modeling methodology is an effective and accurate way of modeling temperaturedependent PL of GaN epilayers grown on PSS. The results of the study suggest that ANN modeling methodology can be used to accurately predict the temperature-dependent PL of GaN epilayers grown on PSS. This means that it may be possible to reduce the number of required experimental measurements by using the ANN model to predict PL intensity at different temperatures, based on a smaller set of experimental measurements. This could potentially save time and resources, while still obtaining accurate information about the optical behavior of GaN-based materials at different temperatures.
Influence of Highly Efficient Carbon Doping on AlxGa1? xAs Layers with Different Al Compositions (x) Grown by MOVPE
(27.06.2023) Pertikel, İzel; Kekül, Reyhan; Altuntaş, İsmail; Gür, Emre; Demir, İlkay
Carbon (C)-doped aluminum gallium arsenide ( AlxGa1−xAs) epitaxial layers with different aluminum (Al) concentrations have been grown on gallium arsenide (GaAs) substrates by metalorganic vapor phase epitaxy (MOVPE) technique. The impact of varying carbon tetrabromide ( CBr4) flow rates on the electrical properties of AlxGa1− xAs materials with different Al compositions has been investigated. High-resolution x-ray diffraction (HRXRD) measurement and a Hall effect measurement system have been used to determine the Al compositions and to evaluate the electrical properties. It has been found that the carrier density increases and the mobility decreases by increasing the flow rate of CBr4 and changing Al compositions up to a certain point. In contrast, at higher Al compositions, a decrease in carrier density and an increase in mobility have been observed with increasing CBr4 flow rate. Since these observed trends require to be analyzed in more detail, x-ray photoelectron spectroscopy (XPS) has been used to analyze the elements in the structure. From the XPS results, it has been shown that the atomic concentration of the arsenic in the structure decreased with the increase in CBr4 flow rates. In addition, it has been shown that the Al composition in the AlxGa1− xAs material obtained from the XRD results increases with the increase in the atomic concentration of the arsenic. Accordingly, a linear increase in carrier concentration is shown with increasing Al composition. This increase is explained by the effect of the Al–C bond content on the electrical properties of AlxGa1− xAs.
Effect of substrate temperature on Raman study and optical properties of GeOx/ Si thin films
(14.10.2023) Baghdedi, Dhouha; Hopoğlu, Hicret; Demir, İlkay; Altuntaş, İsmail; Abdelmoula, Najmeddine; Şenadım, Tüzemen Ebru
In this study, GeOx thin films were deposited onto Si substrates using the RF magnetron sputtering method. We looked at how the temperature of the substrate affected the Raman spectra and optical characteristics of GeOx thin films. X-ray diffraction was utilized to examine the crystal structure, and a scanning electron microscope was utilized to measure the thickness. In order to investigate the local structure and bonding characteristics, Raman spectroscopy was used. The refractive index, extinction coefficient, and dielectric parameters were calculated using spectroscopic ellipsometry for the 300–1100 nm spectral region. Refractive index and extinction coefficient spectral patterns were discovered by using a sample-air optical model to analyze the experimental ellipsometric data. Notably, a considerable rise in the refractive index was accompanied by a rise in substrate temperature.
High-quality AlN growth: a detailed study on ammonia flow
(25.01.2023) Yolcu Gamze; Koçak Merve Nur; Ünal Dudu Hatice; Altuntaş İsmail; Demir İlkay
High crystalline and optical quality aluminum nitride (AlN) films with thin thickness have been grown on Al2O3 by MOVPE (metal-organic vapor phase epitaxy) and the NH3 flow rate has been changed to improve the morphology and quality of the films. Some characterization types of equipment such as atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), and Raman spectroscopy have been carried out to investigate the effect of different NH3 flow rates on surface morphology, roughness, and crystal quality of AlN, respectively. Unlike in the literature, in situ optical reflectance measurements have been given depending on NH3 flow rate and optical characterization has been performed by UV–VIS–NIR spectrophotometry. The well-defined interference patterns in the optical transmittance graph report a sharp interface between AlN and Al2O3. Also, all obtained samples have a sharp absorption edge that shows the quality of the films, but Sample B with 900 sccm NH3 flow has the sharpest absorption edge because it has high optical quality and low defect. The RMS (root mean square), DS (screw-type dislocation density), and DE (edge-type dislocation density) values of AlN with 900 sccm NH3 flow are 0.22 nm, 7.86 [ 107 , and 1.68 [ 1010 cm-2, respectively. The results obtained are comparable to the literature.
Modeling of temperature?dependent photoluminescence of GaN epilayer by artificial neural network
(22.06.2023) Şenadım Tüzemen Ebru; Yüksek Ahmet Gürkan; Demir İlkay; Horoz Sabit; Altuntaş İsmail
Artificial neural networks (ANNs) are a type of machine learning model that are designed to mimic the structure and function of biological neurons. They are particularly well-suited for tasks such as image and speech recognition, natural language processing, and prediction tasks. The success of an ANN in modeling a particular dataset depends on factors such as the size and quality of the dataset, the complexity of the model, and the choice of training algorithms. High representation rate of a system in the data set can improve the performance of the ANN model. The study we described is focused on using artificial neural networks (ANNs) to model temperature-dependent photoluminescence (PL) characterization of GaN epilayers grown on patterned sapphire substrates (PSS) using the metalorganic chemical vapor deposition (MOCVD) technique. The ANN model is trained using temperature and wavelength as input parameters and intensity as the output parameter, with the goal of accurately predicting the PL intensity of the GaN epilayer as a function of temperature and wavelength. The model is trained using a large set of experimental data and then tested using data that was not presented to the model during training. The results of the study suggest that ANN modeling methodology is an effective and accurate way of modeling temperaturedependent PL of GaN epilayers grown on PSS. The results of the study suggest that ANN modeling methodology can be used to accurately predict the temperature-dependent PL of GaN epilayers grown on PSS. This means that it may be possible to reduce the number of required experimental measurements by using the ANN model to predict PL intensity at different temperatures, based on a smaller set of experimental measurements. This could potentially save time and resources, while still obtaining accurate information about the optical behavior of GaN-based materials at different temperatures.
Influence of Highly Efficient Carbon Doping on AlxGa1? xAs Layers with Different Al Compositions (x) Grown by MOVPE
(27.06.2023) İzel Pertikel; Reyhan kekül; İsmail Altuntaş; Emre Gür; İlkay Demir
Carbon (C)-doped aluminum gallium arsenide ( AlxGa1−xAs) epitaxial layers with different aluminum (Al) concentrations have been grown on gallium arsenide (GaAs) substrates by metalorganic vapor phase epitaxy (MOVPE) technique. The impact of varying carbon tetrabromide ( CBr4) flow rates on the electrical properties of AlxGa1− xAs materials with different Al compositions has been investigated. High-resolution x-ray diffraction (HRXRD) measurement and a Hall effect measurement system have been used to determine the Al compositions and to evaluate the electrical properties. It has been found that the carrier density increases and the mobility decreases by increasing the flow rate of CBr4 and changing Al compositions up to a certain point. In contrast, at higher Al compositions, a decrease in carrier density and an increase in mobility have been observed with increasing CBr4 flow rate. Since these observed trends require to be analyzed in more detail, x-ray photoelectron spectroscopy (XPS) has been used to analyze the elements in the structure. From the XPS results, it has been shown that the atomic concentration of the arsenic in the structure decreased with the increase in CBr4 flow rates. In addition, it has been shown that the Al composition in the AlxGa1− xAs material obtained from the XRD results increases with the increase in the atomic concentration of the arsenic. Accordingly, a linear increase in carrier concentration is shown with increasing Al composition. This increase is explained by the effect of the Al–C bond content on the electrical properties of AlxGa1− xAs.
Effect of substrate temperature on Raman study and optical properties of GeOx/ Si thin films
(14.10.2023) Baghdedi Dhouha; Hopoğlu Hicret; Demir İlkay; Altuntaş İsmail; Abdelmoula Najmeddine; Şenadım Tüzemen Ebru
In this study, GeOx thin films were deposited onto Si substrates using the RF magnetron sputtering method. We looked at how the temperature of the substrate affected the Raman spectra and optical characteristics of GeOx thin films. X-ray diffraction was utilized to examine the crystal structure, and a scanning electron microscope was utilized to measure the thickness. In order to investigate the local structure and bonding characteristics, Raman spectroscopy was used. The refractive index, extinction coefficient, and dielectric parameters were calculated using spectroscopic ellipsometry for the 300–1100 nm spectral region. Refractive index and extinction coefficient spectral patterns were discovered by using a sample-air optical model to analyze the experimental ellipsometric data. Notably, a considerable rise in the refractive index was accompanied by a rise in substrate temperature.
Theoretical analyses of the carrier localization effect on the photoluminescence of In-rich InGaAs layer grown on InP
(2022) Marva Ben Arbia, Bedreddine Smiri, DEMİR İLKAY, Faouzi Saidi, ALTUNTAŞ İSMAİL, Fredj Hassen, Hassen Maaref,
The free buffer InGaAs/InP structure has been elaborated by Metal Organic Vapor Phase Epitaxy (MOVPE). High indium content is chosen to reduce the bandgap energy of the ternary material with direct bandgap to be promoted for Infrared optoelectronic devices. In this work, the temperature dependent photoluminescence (TDPL) analysis of In-rich InxGa1− xAs (x = 0.65: S1, x = 0.661: S2, and x = 0.667 S3) samples is of the central focus. The S-shaped behavior recorded at low temperature range in the III-V ternary is quantitatively studied herein by Localized State Ensemble (LSE) model. A comparison between the semi-empirical evolution of luminescence versus temperature and our numerical simulation proves the adequacy of computational details, used in LSE model, in well reproducing the S-shape feature. The numerical simulation well matched with PL spectra proving that the localization phenomenon is stronger when increasing the Indium mole fraction. The clustering effect in In-rich structure seems to be beneficial for enhancing the carrier localization within InxGa1− xAs by localizing carriers from away extended defects that behave probably as non-radiative centers. This is indicative of the utmost importance of localization phenomenon in trapping carriers within localized states instead of dislocations and defects, owing to clustering of indium atoms.
Linear and nonlinear optical properties of a superlattice with periodically increased well width under electric and magnetic fields
(Elsevier, 14.04.2022) Öztürk, Ozan
In this paper, we have studied the electronic and optical properties of GaAs/AlxGa1-xAs superlattice with periodically increased well width. Under effective mass approximation, the finite element method is used to obtain wavefunctions and corresponding energy eigenvalues for several electric field (F) and magnetic field (B) values. We have shown that the increasing well width has a major effect on the localization of the first two energy states. The direction of the applied electric field shifts the localization position of the probability density of electrons to the left and right. For B = 0 (according to the parameters used), F = 5 kV/cm (especially for the difference between the first two energy levels (E12)) is a critical value. While the E12 value decreases in the range from 30 kV/cm to 5 kV/cm, it increases for the 5 < F < 30 kV/cm range. This behavior causes a red or blue shift in the optical spectrum. Also, F = 30 kV/cm causes more change in the structure than F = 30 kV/cm. In addition, the localization of the electrons is observed in the center of the superlattice under applied magnetic fields. The optical absorption coefficients and the refractive index changes are affected by applied F and B intensities. We can say that the electro-optical features of the superlattice have changed significantly with the combined effect of F and B values. This is desired for semiconductor optical device applications to have stable performances.
In-situ and ex-situ face-to-face annealing of epitaxial AlN
(26.06.2022) Merve Nur Koçak; Kağan Murat Pürlü; İzel Pertikel; İsmail Altuntaş; İlkay Demir
AlN films have been deposited on c-plane sapphire substrates by metalorganic-vapor-phase-epitaxy (MOVPE). The changes in the film structure have been investigated by applying different annealing processes which are exsitu rapid thermal annealing (RTA) and in-situ process after the nucleation-layer (NL). The AlN nucleation-layer grown on sapphire has been annealed face-to-face with ex-situ (RTA) process for 3 min and with in-situ process for 3 h, then pulsed-atomic-layer-epitaxy AlN film has been grown at a high temperature. The samples have been characterized by high-resolution X-ray diffraction, atomic force microscopy, Ultraviolet–visible spectrometry, and Raman scattering to examine the structural properties, surface morphology, and optical properties. The sample annealed with the ex-situ (RTA) process, where rapid diffusion took place, has reached larger grain sizes and the dislocation density has decreased as the grain boundary decreased. Although better crystal quality has been obtained with the ex-situ (RTA) process, it has been observed that the surface roughness of the sample annealed with the ex-situ (RTA) process is higher than that of the sample annealed with the in-situ process. Considering the results, a schematic prediction of the growth process after face-to-face annealing has been proposed. Experimental findings have shown that different annealing processes after growing the AlN-NL have a great effect on the properties of the AlN.

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