Improvement Of Crystalline Quality Research Articles

Polarity control and crystalline quality improvement of AlN thin films grown on Si(111) substrates by molecular beam epitaxy

We attain N-polar and Al-polar AlN thin films on Si(111) substrates by plasma-assisted molecular beam epitaxy. The polarity of AlN epilayers has been validated by wet chemical etching using tetramethylammonium hydroxide and by the direct cross-sectional observation of atomic stacking under high-angle annular dark-field scanning transmission electron microscopy. For the 290 nm-thick as-grown N-polar AlN epilayer, x-ray diffraction (XRD) (002) and (102) ω rocking curve peak full width half maximums (FWHMs) are 475 and 1177 arcsec, and the surface mean square roughness (RMS) is 0.30 nm. We flipped the polarity using the metal-flux-modulation-epitaxy (MME) strategy. The MME strategy promotes anti-phase boundaries (APBs) on the {22¯01} crystalline planes instead of commonly observed lateral planar APBs in AlN epilayers. Merging of the tilted APBs at ∼50 nm leads to a complete Al-polar surface. For the 180 nm-thick Al-polar AlN epilayer, XRD (002) and (102) peak FWHMs are 1505 and 2380 arcsec, and the surface RMS is 1.41 nm. Strain analysis by XRD and Raman spectroscopy indicates a uniform tensile strain of 0.160% across the N-polar AlN epilayer surface and a strain distribution of 0.113%–1.16% through the epilayer. In contrast, the Al-polar AlN epilayer exhibits a much broader tensile strain distribution of 0.482%–2.406% along the growth direction, potentially due to the interaction of polarity inversion and strain relaxation.

Microstructural evolution and formation of defect complexes in diamond films by nitrogen-containing plasma

Abstract The morphology and crystalline quality of polycrystalline diamond samples were studied by systematically varying the flowrate of nitrogen gas in the microwave plasma. A slight improvement in both crystallite size and crystalline quality is observed for a low concentration of 0.5 sccm nitrogen. With a further increase in nitrogen concentration, diamond switches from micro-crystalline (MCD) to nanocrystalline (NCD) with a nitrogen flow of 2.5 sccm (10% of methane concentration). The surface roughness of the sample is found to depend strongly on the crystallite size of the sample. Extensive spectroscopic studies have been done to understand the presence and formation of different defect complexes in diamond. The presence of nitrogen-containing defect complexes has been studied thoroughly and their concentration has been found to be limited by the solubility limit rather than the availability of reactants in the gas environment. In contrast, the effect these complexes have on the strain of the diamond film is found to be negligible. Optical emission spectroscopy (OES) of the plasma reveals the presence of C2 dimers as well as C-N radicals. However, they have little role in modifying diamond grain morphology or crystalline quality.

A comprehensive examination of structural modifications, optical characteristics, and electrochemical analysis of magnesium‐doped dysprosium chromite

AbstractBackgroundThis study focuses on the synthesis of magnesium‐doped dysprosium chromite via a sol‐gel method. The investigation aims to understand the morphological and structural properties of the synthesized nanochromates. Key techniques employed include x‐ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy.AimsThe primary aim is to analyze the structural characteristics of MgxDy1−xCr2O4 nanoparticles with varying Mg doping concentrations (ranging from 0.2 to 0.8). Special attention is given to the crystallinity of the synthesized materials, with the goal of assessing the reliability and reproducibility of the sol‐gel synthesis method.MethodsXRD analysis is employed to identify major diffraction peaks associated with the chromate nanoparticles, providing insights into their crystallinity. SEM imaging allows for the examination of the morphological features of the synthesized materials. Additionally, Raman spectroscopy aids in further understanding the structural properties of the nanochromates.ResultsThe XRD analysis reveals average crystallite sizes for MgxDy1−xCr2O4 nanoparticles at different Mg doping concentrations. Notably, an improvement in crystalline quality is observed with an increase in Mg doping from 0.2 to 0.8, indicating a high level of control achieved in the synthesis process. Cyclic Voltammetry (CV) experiments conducted using a 1M KOH electrolyte and varying scan rates (3 mV/s to 50 mV/s) demonstrate enhanced electrochemical performance of the synthesized nanoparticles.ConclusionThe study concludes that the sol‐gel synthesis method effectively produces MgxDy1−xCr2O4 nanoparticles with controlled morphological and structural properties. The observed improvement in crystalline quality with increasing Mg doping concentration suggests potential applications in fields such as photo‐catalysis, where enhanced crystallinity correlates with improved photo‐catalytic potential for visible light absorption.

Emerging Schemes for Advancing 2D Material Photoconductive-Type Photodetectors.

By virtue of the widely tunable band structure, dangling-bond-free surface, gate electrostatic controllability, excellent flexibility, and high light transmittance, 2D layered materials have shown indisputable application prospects in the field of optoelectronic sensing. However, 2D materials commonly suffer from weak light absorption, limited carrier lifetime, and pronounced interfacial effects, which have led to the necessity for further improvement in the performance of 2D material photodetectors to make them fully competent for the numerous requirements of practical applications. In recent years, researchers have explored multifarious improvement methods for 2D material photodetectors from a variety of perspectives. To promote the further development and innovation of 2D material photodetectors, this review epitomizes the latest research progress in improving the performance of 2D material photodetectors, including improvement in crystalline quality, band engineering, interface passivation, light harvesting enhancement, channel depletion, channel shrinkage, and selective carrier trapping, with the focus on their underlying working mechanisms. In the end, the ongoing challenges in this burgeoning field are underscored, and potential strategies addressing them have been proposed. On the whole, this review sheds light on improving the performance of 2D material photodetectors in the upcoming future.

Ag nanoparticle assisted vertically aligned β-Ga2O3 nanowire deposited by GLAD technique for ultrafast photodetection

In this study, we report the fabrication of Silver (Ag) nanoparticle (NP) assisted vertically oriented β-Ga2O3 nanowires on Silicon (Si) - substrate by the Glancing angle deposition (GLAD) technique. The fabricated samples were annealed at 900 °C. The optoelectronic properties of both As-deposited and annealed devices are studied thoroughly. The sample shows an increase in average crystallite size upon annealing with a decrease in lattice strain and dislocation density. FEG-SEM image confirms the growth of well-aligned vertically oriented nanowires with Ag NP in the midway of each nanowire. The UV–Vis absorption spectra show that Ag NP's presence results in the appearance of a significant absorption hump in the visible range, thereby broadening the light absorption capability of β-Ga2O3. The improvement in crystalline quality and reduction in defects after annealing resulted in a better response for the annealed device. These results indicate that annealing the Ag NP-assisted β-Ga2O3 NW device could become a feasible option for high-speed photodetectors, as it demonstrates a faster photoresponse time and a lower turn-on voltage.

The microstructural evolution of sputtered ZnO epitaxial films to stress-relaxed nanorods

Epitaxial ZnO thin films and nanorods were grown on c-sapphire substrate by reactive sputtering of Zn in Ar-O2 atmosphere at substrate temperatures ranging from near room temperature to 700 °C. Scanning electron microscopy showed that with increase in substrate temperature, the morphology transformed from columnar films to vertically aligned ZnO nanorods. High resolution x-ray diffraction revealed improvement in crystalline and epitaxial quality with increase in substrate temperature, along with the decrease of edge dislocation density from 5 × 1012 cm−2 to 8 × 1010 cm−2. The films grown near room temperature showed large hydrostatic strain (∼6 × 10−3) and compressive intrinsic biaxial stress (-0.8 GPa), which decreased substantially with increase in substrate temperature, due to the desorption of excess oxygen and reduction in edge dislocation density. Above the substrate temperature of 500 °C, the intrinsic biaxial stress reversed from compressive to mildly tensile in the case of nanorods, due to the intrinsic tensile stress, originating from crystallite coalescence. Raman measurements correlate well with the changes in biaxial stress and confirm the improvements in crystallinity and epitaxial quality of nanorods grown at higher temperatures. Room temperature photoluminescence of the ZnO films showed weak near-band-edge emission, which enhanced drastically in the case of nanorods due to their superior microstructure and epitaxial quality.

Deep UV transparent conductive Si-doped Ga2O3 thin films grown on Al2O3 substrates

β-Ga2O3 is attracting considerable attention for applications in power electronics and deep ultraviolet (DUV) optoelectronics owing to the ultra-wide bandgap of 4.85 eV and amendable n-type conductivity. In this work, we report the achievement of Si-doped β-Ga2O3 (Si:β-Ga2O3) thin films grown on vicinal α-Al2O3 (0001) substrates with high electrical conductivity and DUV transparency of promising potential as transparent electrodes. The use of Al2O3 substrates with miscut angles promotes step-flow growth mode, leading to substantial improvement of crystalline quality and electrical properties of the Si:β-Ga2O3 films. A high conductivity of 37 S·cm−1 and average DUV transparency of 85% have been achieved for 0.5% Si-doped film grown on a 6° miscut substrate. High-resolution x-ray and ultraviolet photoemission spectroscopy were further used to elucidate the surface electronic properties of the grown Si:β-Ga2O3 films. An upward surface band bending was found at the surface region of Si:β-Ga2O3 films. Interestingly, all the Si:β-Ga2O3 films have a very low work function of approximately 3.3 eV, which makes Si:β-Ga2O3 suitable materials for efficient electron injection. The present Si:β-Ga2O3 films with high conductivity, DUV transparency, and low work function would be useful as the DUV transparent electrode to develop advanced DUV optoelectronic devices.

Growth mode modulation and crystalline quality improvement of highly relaxed n-Al0.6Ga0.4N on high-temperature-annealing AlN/sapphire template via SiH4-pretreatment

High-quality AlGaN-based film is the key to attain efficient deep ultraviolet emitters. In this study, we developed a silane-pretreatment method to modulate the growth mode of n-Al0.6Ga0.4N on high-temperature-annealing AlN/sapphire template (HTA-AlN) and improve the crystalline quality. It’s found that pretreating the surface of HTA-AlN template by SiH4 could disturb the pseudo-crystal epitaxy of n-Al0.6Ga0.4N and prompt the 3D growth at the AlGaN/AlN interface. The stress of n-Al0.6Ga0.4N was thus released rapidly by fresh-born dislocations. During the following growth, the growth mode of n-Al0.6Ga0.4N with SiH4-pretreatment transformed quickly from 3D to 2D, and the stress was released gradually because of the dislocation inclination. Besides, the threading dislocation density of 6 µm-thick n-Al0.6Ga0.4N with SiH4-pretreatment was reduced to 8.6 × 108 cm−2, which was one third of that without SiH4-pretreatments. This work paves the way for preparation and improvement of the DUV emitters.

Investigation of properties of Ta-doped Ga2O3 films prepared with seed layers

Ga2O3 is a promising ultra-wide bandgap semiconductor as a feasible candidate for power electronics, photodetectors, and sensors. Controlling electrical properties through doping is the key to its application in semiconductor devices. In this work, Ta-doped Ga2O3 films were prepared by radio frequency (RF) magnetron sputtering with seed layers. Effects of the thickness of seed layers on the microstructure, morphology, optical and electrical properties of Ta-doped Ga2O3 films were investigated. The fabricated Ta-doped Ga2O3 films exhibited polycrystalline structure with uniform and smooth surface and high optical transmittance (＞80 %) in the visible light region. The results showed that seed layers with appropriate thickness (∼20 nm) is beneficial to the improvement of crystalline quality and electrical properties of Ta-doped Ga2O3 films.

Parasitic behavior of different V/III ratios on the properties of InGaN/GaN heterostructures by MOCVD technique

In this study, InGaN/GaN heterostructures were grown on a c-plane flat sapphire substrate (FSS) by using the metalorganic chemical vapor deposition (MOCVD) technique. The flow rates of the ammonia gas varied from 9 SLM to 24 SLM for the growth of InGaN thin film, which was equivalent to the V/III ratio of 6211–16562. Results indicated that a higher V/III ratio promotes parasitic behavior by hydrogen dissociated from ammonia. The parasitic behavior from hydrogen species etches the InN away from the growing surface and transforms the growth morphology from 3D islands to 2D growth mode. A slight reduction in indium composition was observed when increasing the V/III ratio. Next, more stable bandgap energy was observed for the InGaN thin films grown at higher V/III ratios. Improvements in electrical properties in terms of electron mobility and sheet resistance were observed at a higher V/III ratio which is associated with the improvement of crystalline quality and less defect density at a higher V/III ratio. The correlation of strain and carrier density of the thin films was further discussed. It was concluded that the growth of high crystalline quality and thick InGaN thin film was possible for solar cell applications at higher V/III ratio growth conditions.

Integration of single layer graphene into CZTS thin film solar cells

In this study, CZTS samples were produced on Mo and graphene/Mo coated glass substrates using quaternary target. The CZTS thin films deposited by RF magnetron sputtering were annealed using rapid thermal processing (RTP) method in sulphur atmosphere at 500, 525, and 550 °C so as to obtain glass/Mo/CZTS and glass/Mo/graphene/CZTS (g-CZTS) structures. The obtained CZTS and g-CZTS thin films were then characterized by several methods such as EDX, XRD, Raman spectroscopy, SEM etc. The EDX data demonstrated that all CZTS thin films had Cu poor composition regardless of the sulfurization temperature and increasing the temperature led to Sn loss from the films. Diffraction peaks of kesterite CZTS phase were observed in all the samples; additionally, SnS and CuS secondary phases were also observed in CZTS samples annealed at 500 °C. The crystallite size of the CZTS thin films were found to be increasing with both increasing annealing temperature and use of graphene film as an inter-layer. The creation of kesterite phase with a very small CTS phase in all the samples were verified by the Raman spectroscopy measurement. The SEM images of the samples indicated that using graphene improves the crystalline quality of the CZTS films and contributes to forming more compact, homogenous and larger crystal structure. The determined optical band gap values varied from 1.41 to 1.44 eV depending on the Sn-content of the samples. The produced solar cells selected from the more promising absorber layers showed that implementing graphene in CZTS cell structure enhanced the conversion efficiency from 2.40% to 3.52% due to improvement of crystalline quality of the absorber layer.

Effects of growth temperature for in-situ deposited SiNx interlayer on structural and optical properties of semipolar ([formula omitted]) AlGaN films

The dependence of surface morphology, crystalline quality, and optical properties on the growth temperature of in-situ deposited SiNx interlayers in the semipolar (112¯2) AlGaN film was investigated intensively. The in-situ SiNx deposited interlayer was consisted of irregular ultra-thin SiNx nano-scale island-like structures as verified by using scanning electron microscope and energy dispersive spectroscopy. As the growth temperature of the in-situ deposited SiNx interlayer was increased from 700 to 1100 °C, the root mean square roughness of the semipolar (112¯2) AlGaN film increased from 0.72 to 0.87 nm. It was revealed that significant improvements in surface morphology, crystalline quality, and optical properties of the semipolar (112¯2) AlGaN films could be achieved with the insertion of an in-situ deposited SiNx interlayer grown at a temperature between 800 and 1000 °C. These achievements are owing to the formation of the SiNx nano-scale island-like structures that like the well-known patterned sapphire substrate played a crucial role in the reduction of the basal-plane stacking faults (BSFs) and the suppression of the BSFs- and other defects-related emissions in the semipolar (112¯2) AlGaN films.

The Mechanisms of AlGaN Device Buffer Layer Growth and Crystalline Quality Improvement: Restraint of Gallium Residues, Mismatch Stress Relief, and Control of Aluminum Atom Migration Length

The mechanisms of AlGaN device buffer layer growth were studied. Gallium residues in the reactor chamber may be harmful to the quality of the AlN strain modulation layer, which eventually worsens the AlGaN buffer layer. By restraining the gallium residues, the crystalline quality of the AlGaN layer is markedly improved. In addition, enhancing stress relief in nucleation and coalescence stages will reduce the edge dislocations induced by strain relaxation in the 2D growth stage. A slower precursor flow rate can promote the stress relief in nucleation and coalescence stages. By comparison, a suitable suppression of Al atoms’ surface migration can decrease surface roughness, which can be realized by increasing the precursor flow rate. Eventually, we obtained a AlGaN buffer layer having both low edge dislocation density and a flat surface using a two-step growth method.

Synthesis of ZnO nanoparticles at room temperature with enhanced ultra‐violet photoluminescence

ZnO nanoparticles (NPs) have attracted a lot of attention due to the possibility of their applications in different fields including optoelectronics, photonics, biosensing, catalytic, etc. Most of the applications require devices made of good quality of NPs. However, synthesis of device grade NPs is always challenging. Here, improvement of crystalline quality of the ZnO NPs has been demonstrated with a very simple procedure. ZnO NPs of average crystallite size of ~11.5 nm with optical band gap of ~3.44 eV have been synthesized in room temperature following the co-precipitation method by either varying the concentration of KOH or time of synthesis. For both the cases, change in average size of NPs has not been found to change significantly. This is mainly because the required heat energy to grow the size has not been provided externally. However, the increase of concentration of KOH or time of preparation has been found to improve the quality of the ZnO crystallites. The improvement of crystalline quality has been argued as due to the availability of enough KOH or the time to repair the defects on the surface of the NPs. Improvement of crystalline quality has been found to result in an enhancement of intensity of the ultraviolet (UV) photoluminescence (PL) emission band over the visible PL emission band of ZnO. The defect mediated visible PL emission is always considered as loss. The enhancement is ~2-fold. Such large enhancement can be utilized for the fabrication of optoelectronic devices and others based on ZnO NPs synthesized at room temperature.

Effect of tempering on the metallurgical, structural, and thermal properties of AISI/SAE 1030 steel

Steel exhibits changes in their phase structure; in the thermal and mechanical properties due to thermal treatments. This work analyzed the influence of tempering temperature on these properties for 1030 steel. Samples were quenched at 850 ºC. Then, they were tempered for 2 h at 200 (QT200), 400 (QT400), 600 (QT600), and 650 ºC (QT650). Thermal, structural, morphological, and mechanical properties of these samples were analyzed and correlated. SEM images show changes in martensite morphology and the carbides presence as a function of tempering temperature. QT600 and QT650 samples with high tempering temperature exhibit the highest presence of carbides. X-ray diffraction shows no changes in the steel structure, but changes in lattice parameters, and crystalline quality improvement. Thermal diffusivity was determined and correlated with the structural changes by temperature effect. The heat transport properties increase as a function of the tempering temperature due to in part because of the structural reorganization, which allows heat transport. Due to the crystal stress release and the martensite tempered the hardness decreases as a function of the tempering temperature.

Annealing induced carrier activation and PL enhancement in Ge-on-Si grown by low temperature MBE

A series of phosphorus-doped Ge-on-Si were grown by molecular beam epitaxy and then annealed at different temperatures to investigate dopant activation and diffusion. The X-ray diffraction and reciprocal space mapping results show that an in-plane tensile strain up to 0.26% was introduced by annealing. Hall effect measurement results revealed that annealing can effectively activate the dopants, and 700 °C is an optimized annealing temperature. High mobility of 300–1000 cm2/V·s for n-type Ge is achieved at room temperature. Secondary ion mass spectrum profile shows that the diffusion coefficient for these P-doped Ge samples is on the order of 10-14 cm2/s after annealing at 700 °C. Significant photoluminescence enhancement in the samples annealed at 700 °C was observed and is attributed to the crystalline quality improvement, residual tensile strain and n+ doping.

The influence of high-temperature nitridation process on the crystalline quality of semipolar [formula omitted] GaN epitaxial films

Semipolar (112‾2) GaN epitaxial films were grown on m-plane sapphire substrates by metal-organic chemical vapor deposition and additional high-temperature nitridation was introduced during the growth. The growth mechanism, surface microtopography, and the full width at half maximum (FWHM) of X-ray rocking curves (XRCs) of on-axis and off-axis (112‾2) GaN planes were investigated. The results demonstrate that additional high-temperature nitridation process could reduce surface roughness and anisotropy, and suppress the other orientations, and partially improve the crystalline quality of (112‾2) GaN epitaxial films. The XRCs FWHM of the off-axis (112‾2) GaN planes decrease and show a different varying tendency after additional high-temperature nitridation process associated with the partial dislocations and basal plane stacking faults (BSFs). The results of the modified Williamson-Hall (W–H) analysis and photoluminescence spectrum show the BSFs increased while the partial dislocations decreased after an additional high-temperature nitridation process. The improvement of crystalline quality was mainly correlated to the reduction of partial dislocations.

Improved surface morphology and crystalline quality of semi-polar ([formula omitted]) AlN epilayer with dual moderate-temperature-grown AlN interlayers

Semi-polar (112‾2) AlN epilayers have been grown on (101‾0) m-plane sapphire substrates with the help of dual moderate-temperature-grown (MTG) AlN interlayers by metal-organic chemical vapor deposition. Significant improvements in both surface morphology and crystalline quality of the semi-polar (112‾2) AlN epilayers have been achieved with the insertion of the MTG AlN interlayers due to the formation of nano-scale patterned substrate-like structure and the reduction in the basal-plane stacking faults with their associated partial dislocations. The effect of the variation in the thickness of the MTG AlN interlayer ranged from 20 to 100 nm was investigated in detail based on the characterization results of the atomic force microscopy (AFM) and X-ray diffraction. It was revealed that all the semi-polar AlN epilayer samples grown with the dual AlN interlayers on (101‾0) m-plane sapphire substrates were uniquely [112‾2]-oriented regardless of the variation in the thickness of the MTG AlN interlayer. Moreover, it was found that the most remarkable reduction in the surface roughness and the most effective improvement of structural quality could be obtained when the thickness for the inserted dual MTG AlN interlayers was approximately 80 nm. In fact, the smallest root mean square roughness of the semi-polar (112‾2) AlN epilayer surface was determined to be 1.4 nm by AFM measurement.

The performance improvement of AlGaN/GaN heterojunction by using nano-patterned sapphire substrate

AlGaN/GaN heterojunction structures grown on nano-scale patterned sapphire substrates and planar sapphire substrates were investigated. The X-ray diffraction rocking curves indicated an improvement of crystalline quality by using sapphire substrate with concave nano-scale patterns. The surface morphology improvement of samples was characterized using atomic force microscope and scanning electron microscope. The transmission electron microscope results showed a significant dislocation reduction. The Hall-effect measurement confirmed that the mobility of two-dimensional electron gas was obviously improved.

Effects of post-deposition annealing in oxygen ambient of RF magnetron sputtered Ga<SUB align="right">2O<SUB align="right">3 thin film

An investigation on the radio frequency magnetron sputtered gallium oxide (Ga2O3) thin films on Si (100) subjected to different post-deposition annealing temperatures of 400, 600, 800, and 1000°C for 60 min in oxygen ambient was carried out in this work. Grazing incidence X-ray diffraction (GIXRD) revealed the formation of polycrystalline Ga2O3 thin films with an improvement in crystalline quality as the post-deposition annealing temperature was enhanced from 400 to 1000°C. The improvement in crystalline quality of Ga2O3 thin films was related to a reduction in the concentration of oxygen vacancies, wherein energy-dispersive X-ray spectroscopy has revealed an increment in atomic percentage of oxygen from 62.63 to 66.66 as a function of post-deposition annealing temperature. The changes from compressive to tensile microstrain induced on the investigated Ga2O3 thin films during post-deposition annealing at/beyond 800°C have revealed the occupancy of more oxygen vacancies. Thus, an increment in values of direct and indirect bandgap of Ga2O3 thin films was attained with respect to post-deposition annealing temperature. Nonetheless, it was perceived that the formation of interfacial layer was exaggerated at 1000°C, wherein an exceptionally low leakage current density has been demonstrated by Ga2O3 thin films annealed at 1000°C.