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Li 2 O–ZnO–B 2 O 3 -WO 3 (LZBW) sealing glasses for Si substrates were prepared and the effect of WO 3 on the structure, thermal properties, and sintering behaviour was investigated. As the WO 3 increases from 0 to 12 mol%, the glass transition temperature and softening temperature reach the lowest values of 448 °C and 479 °C, respectively, at which time the glass network has the lowest degree of polymerization. The thermal expansion coefficient increases from 6.959 × 10−6/°C to 8.476 × 10−6/°C with increasing WO 3 contents. It is verified that the introduction of WO 3 can effectively improve the conductivity. The sealing property of the glasses was evaluated by the wetting angle of the glasses after co-sintering with Si substrate for 10 min at 860 °C, and the 25Li 2 O-7ZnO-2.7Bi 2 O 3 -1.3P 2 O 5 -55B 2 O 3 -9WO 3 glass had the minimum wetting angle of 34.07°. The excellent thermal properties, conductivity, and wetting behaviour of the LZBW glasses make it a potential material as a binder material for positive silver pastes. [ABSTRACT FROM AUTHOR]

Pb[Zr,Ti]O 3 (PZT) thin films with the Zr/Ti ratio of 45/55, 52/48, and 60/40 (PZT(45/55), PZT(52/48), and PZT(60/40), respectively) are deposited on (001)SrRuO 3 /(001)Pt/ZrO 2 /Si by sol-gel method. We confirm that the epitaxial (001)Pt electrode facilitate the epitaxial growth of the PZT thin films along the c -axis direction. Basic characteristics such as structural, dielectric, and ferroelectric properties are examined. Furthermore, direct and converse piezoelectric properties are evaluated using effective transverse piezoelectric coefficients, | e 31, f |. In particular, the epitaxial PZT thin films manifest a dependence of the converse | e 31, f | on applied voltages with the values as follows; 9.7–11.5 C/m2, 11.2–12.5 C/m2, and 11.7–12.3 C/m2 for the epitaxial PZT(45/55), PZT(52/48), and PZT(60/40), respectively. Moreover, by analyzing bias-resolved in-situ reciprocal space map (RSM) obtained from synchrotron radiation X-ray diffraction (SR-XRD) which allows for the understanding on the transition of crystal structures, we explore the voltage-induced contributions for the converse | e 31, f |. [ABSTRACT FROM AUTHOR]

This article proposes a parameter extraction method suitable for Si substrate based GaN HEMT small signal equivalent circuit models. The proposed method is based on a swarm intelligence optimization algorithm, which improves efficiency and accuracy by introducing a slope penalty factor (SPF) method for the objective function, rather than simply minimizing the error between simulation and measurement. By using PSO, WOA, and PNC-WOA for validation, we have demonstrated the advantages of the SPF method in extracting small signal parameters using swarm intelligence optimization algorithms. It is suitable for complex small-signal models that can describe the GaN HEMT-on-Si substrates, even if working up to 40 GHz. [ABSTRACT FROM AUTHOR]

Porous SiO2 film has been widely studied due to its extensive applications in many fields. This paper presents a newly produced porous SiO2 film made by traditional sol–gel method. Bare Si and Si with SiO2 buffer layer were used as substrate. The SiO2 buffer layer was 500 nm in thickness and was grown by thermal oxidization. The structural properties of SiO2 aerogel films spin-coated on both materials were observed by optical microscope (OM) and scanning electron microscope (SEM). Results reveal that the surface of SiO2 aerogel films on bare Si is rough and discontinuous. While flat and smooth surface is observed on sample with SiO2 buffer layer. This indicates that by inserting SiO2 buffer layer, the structural property of SiO2 aerogel film deposited on Si is improved. [ABSTRACT FROM AUTHOR]

• Verticle graphene growth from gaseous phase by PECVD. • Verticle orientation of graphene thin films depending on enhancement of plasma. • Fibrous shaped wall growth. • The graphitic structure of graphene thin films. Vertical growth of graphene thin films was achieved on Si (100) substrate employing the sputtering technique. Physical-chemical properties of graphene thin films were examined at annealing temperatures from 500 to 780 °C and flowrate ratios of Ar and C 2 H 2 working gases. The effect of temperature on the growth of graphene thin film, surface morphology, microstructure properties, and chemical state were investigated systematically. The formed graphene thin films were characterized and analyzed using different techniques such as Raman spectroscopy, field emission- and cross-sectional-scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The graphene thin films on the Si substrate exhibited the better growth at the 700 °C and 30:15 (Ar:C 2 H 2) flowrate ratio. Results of Raman spectroscopy showed that the graphene thin films have graphitic structure with crystallite size in the range of 10 to 23 nm. Surface morphology exhibited a wall-like structure with a sheet shape. The CS-SEM images indicated columnar growth of films perpendicular to the film plane. Analysis of the chemical states of C 1 s and O 1 s indicated chemical defects in the graphene thin films, evidenced by the presence of lattice oxygen and non-lattice oxygen ions. [ABSTRACT FROM AUTHOR]

Ga 2 O 3 is an ultrawide-band-gap semiconductor with excellent properties and promising applications in the electronic and optoelectronics. For acting as the substrate for heteroepitaxial Ga 2 O 3 films, Si has the advantages of wafer-level size, cheap price and nice compatibility whereas also perform the disadvantage of large thermal mismatch. In this paper, the apparent flower-like defects are exhibited on the macroscopic surfaces of annealed Ga 2 O 3 films deposited on (100), (110) and (111) oriented Si substrates by atomic layer deposition (ALD) method. The reason is ascribed to the different thermal expansion coefficients between Ga 2 O 3 and Si induced compressive and tensile stresses. The Al 2 O 3 or HfO 2 buffer layer intercalated between Ga 2 O 3 films and Si substrates via successive ALD process suppress the flower-like defects effectively while the surface roughnesses are low to be 1.290 nm and 2.393 nm, respectively. XRD spectra demonstrate that buffer layer indeed relieves the stress of Ga 2 O 3 films on Si substrates while the amorphous Al 2 O 3 has better influence than the polycrystalline HfO 2. The results are helpful to the improvement of growth quality and device property of Ga 2 O 3. • The macroscopic surface morphology of Ga 2 O 3 films on Si with and without buffer layers are compared with each other. • The flower-like defects on the Ga 2 O 3 surface on Si can be suppressed with buffer layer through successive ALD processes. • The results provide a much simple and convenient method to suppress the surface defects of Ga 2 O 3 films on Si substrates. [ABSTRACT FROM AUTHOR]

Determination of pork DNA is essential to avoid the serious allergens imposed by it as well as for halal authentication for certain community. The needed sensor should be able to identify the pork DNA in rapid way and sensitive to ultra-low molarity detection. In this work we developed a surface enhanced Raman spectroscopy sensor (SERS) using silver nanoparticles (AgNPs) on Si matrix. A deep investigation of the effect of the laser wavelength on the sensing efficiency has been performed. Wavelength dependent sensing mechanisms are deliberately studied in the current research. Further the selectivity of sensor towards Pork DNA discrimination is exhibited with Chicken DNA analysis. The developed SERS sensor identifies the Pork DNA down to 13.6 fg/ μL proving its excellent sensitivity. The statistical outfit studies with regard to the developed sensor shows the low values of RSD (∼3%) adding advantage of the developed SERS sensor biosensor. The SERS sensor will definitely serve to be an excellent fast, selective and sensitive tool for onsite screening of meat products to cease the adulteration.

In this work, CdTe polycrystalline thin film was deposited on p-type monocrystalline Si substrate via magnetron sputtering technology without an oxygen portion using a well-designed post-processing method under N2:O2 = 4:1, and then CdTe films were etched on the Si surface by Br2-CH3OH solution to analyze the surface and interfacial characteristics of CdTe/Si such as structure, morphology, optics interdiffusion, and intermediate compounds. X-ray diffraction (XRD) results indicate that the polycrystalline CdTe grow preferentially in the (111) direction, and Raman data demonstrate that the CdTe thin film is rich in tellurium, meaning that CdTe, as a p-type semiconductor material, combined with p-Si to form a composite structure. Meanwhile, photoluminescence (PL) spectra suggest that p-CdTe/p-Si under high thermal processing can effectively remove ~1.40 eV defect level, which indicates that the CdTe layer has a lower recombination center. It is particularly worth mentioning that x-ray photoelectron spectroscopy (XPS), XRD, and Raman analysis confirm the Te–Si intermediate compounds at the CdTe/Si interface, which is very conducive to optimizing the contact characteristics of CdTe/Si, thereby improving the interfacial properties of CdTe/Si. This work reveals a potentially effective way to improve the performance of photoelectric devices by introducing poly-CdTe/Si as a composite structure. [ABSTRACT FROM AUTHOR]

High-quality ε -phase Ga 2 O 3 thin film with a FWHM of 0.68° for the (002) plane in omega scan is grown on Si/AlN composite substrate by MOCVD. The crystal phase evolution and microstructure of Ga 2 O 3 thin films at different temperatures are studied systematically. It is found that Ga 2 O 3 changes from amorphous at 400 °C to ε -phase at 500 °C. As the temperature further rises to 600 °C, it eventually transforms into β -phase. Due to the difference of lattice mismatch, ε -Ga 2 O 3 is crystalline with high crystallinity on the surface of the film, but amorphous at the interface, while β -Ga 2 O 3 is polycrystalline. In addition, ε -Ga 2 O 3 thin films not only have the smoothest surface with roughness of 2.63 nm, but also the content of point defects (such as oxygen vacancies) is significantly reduced compared with that of amorphous and β -Ga 2 O 3 thin films. This work provides important references for the hetero-integration of Si and Ga 2 O 3 by MOCVD, and is beneficial for the development of low cost and high crystal quality Ga 2 O 3 thin films which are suitable for high voltage and ultraviolet optoelectronics. [ABSTRACT FROM AUTHOR]

Even though there have been many experimental attempts and theoretical approaches to understand the process of electromigration (EM), it has not been quantitatively understood for ultrathin structures and at grain boundaries. Nevertheless, we showed recently that it can be used reliably for the formation of single atomic point contacts after careful pre-structuring of the initial Ag nanostructures. The process of formation of nanocontacts by EM down to a single-atom point contact was investigated for ultrathin (5 nm) Ag structures at 100 K by measuring the conductance as a function of the time during EM. In this paper, we compare the process of thinning by EM of structures with constrictions below the average grain size of Ag layers (15 nm) with that of structures with much larger initial constrictions of around 150 nm having multiple grains at the centre constriction prior to the formation of a point contact. Even though clear morphological differences exist between both types of structures, quantized conductance plateaus showing the formation of single point contacts have been observed for both. Here we put emphasis on the thinning process by EM, just before a point contact is formed. To understand this thinning process, the semi-classical regime before the contact reaches the quantum regime was analyzed in detail. For this purpose, we used experimental conductance histograms in the range between 2G0 and 15G0 and their corresponding Fourier transforms (FTs). The FT analysis of the conductance histograms exhibits a clear preference for thinning along the [100] direction. Using well-established models, both atom-by-atom steps and ranges of stability, presumably caused by electronic shell effects, can be discriminated. Although the directional motion of atoms during EM leads to specific properties such as the instabilities mentioned, similarities to mechanically opened contacts with respect to cross-sectional stability were found.

In this article, the Au-free complementary metal oxide semiconductor (CMOS) transistor compatible AlGaN-channel high-electron-mobility transistors (HEMTs) on silicon substrate with 2-kV forward and reverse blocking voltages have been reported. Due to the designed AlGaN epitaxial layers, breakdown voltages (BVs) of the conventional AlGaN-channel HEMTs with $L_{GD} =5$ /10/15/ 20/ $25~\mu \text{m}$ are 420/1070/1590/1920/2000 V respectively, and the values are increased to 760/1420/1980/1990/2000 V by using Schottky-drain technique. The reverse-blocking HEMTs demonstrate reverse blocking voltages of −790/−1300/−1810/−2000 V for ${L}_{GD}=5$ /10/15/ $20~\mu \text{m}$. Meanwhile, the conventional HEMT power figure-of-merit (FOM) of 397 MW/cm2 is the highest FOM for AlGaN-channel HEMTs on silicon, and the Schottky-drain HEMT forward FOM of 384 MW/cm2 and reverse FOM of 321 MW/cm2 are the highest FOM values for all GaN-based reverse-blocking HEMTs on silicon. [ABSTRACT FROM AUTHOR]

Gallium nitride-on-Silicon epitaxy technology has enabled a high level of large-scale GaN integrated manufacturing. However, the poor crystalline quality of GaN on Si substrates dramatically deteriorates device performance. This work demonstrates the application of a buffer layer structure of AlN/3D-GaN with a SiN interlayer to obtain GaN films with high crystalline quality on Si substrates. Transmission electron microscopy and X-ray diffraction reveal reductions in GaN dislocation density. The full width at half maximum values of the X-ray rocking curve for the GaN(0002) and (10–12) planes have decreased from 499 to 710 arcsec to 339 and 350 arcsec, respectively. Ultraviolet photodetectors based on the optimized GaN-on-Si substrates exhibit low dark currents (34 pA@10 V) and high responsivity (6.8 A/W@10 V). Our reported novel buffer architecture provides an important reference for improving the performance of other GaN-based optoelectronics and power electronic devices on Si substrates. • Introducing AlN/3D-GaN with SiN interlayer into GaN films on Si substrates. • The FWHM of GaN (0002) and (10–12) XRCs decrease from 499 and 710 arcsec to 339 and 350 arcsec. • The PDs based on GaN films on substrats reveal a low dark current (34 pA@10 V) and a high responsivity (6.8 A/W@10 V). [ABSTRACT FROM AUTHOR]

• The forming gas (FG) annealing results in a significantly reduction of surface native oxide whereby the amount of Ga–O bonds is decreased demonstrated by the X-ray photoelectron spectra. Hydrogen atoms in H 2 can react with oxygen atoms in the native oxide layer and remove the oxygen to form a surface with oxygen vacancies. Nitrogen molecules in FG can provide nitrogen atoms to fill up these vacancies. Consequently, the removed native oxide layer during FG annealing leads to the formation of a new nitridation layer on the surface. • Compared with N 2 annealing, an on-resistance of 1.68 Ω·mm, a subthreshold swing of 118 mV/dec, a transconductance peak of 513 mS/mm, a gate diode breakdown voltage of surpassing 42 V, and a high current/power gain cutoff frequency (f T / f max) of 165/165 GHz are achieved by the 50-nm InAlN/GaN HEMT annealing by FG H 2 /N 2 on Si substrate. The surface electronic states and defects of gallium nitride based high-electron-mobility transistors (HEMTs) play a critical role affecting channel electron density, electron mobility, leakage current, radio frequency (RF) power output and power added efficiency of devices. This article demonstrates the improved surface properties of InAlN/GaN HEMTs through forming gas (FG) annealing, resulting in a significantly improved electrical properties. The X-ray photoelectron spectra reveals a reduction of surface native oxide after FG H 2 /N 2 annealing whereby the amount of Ga–O bonds is decreased. Compared with N 2 annealing, an on-resistance of 1.68 Ω·mm, a subthreshold swing of 118 mV/dec, a transconductance peak of 513 mS/mm, a gate diode breakdown voltage of surpassing 42 V, and a high current/power gain cutoff frequency (f T / f max) of 165/165 GHz are achieved by the 50-nm InAlN/GaN HEMT on Si substrate. [ABSTRACT FROM AUTHOR]

GaN-on-Si high-electron-mobility transistors (HEMTs) exhibit excellent properties for efficient power conversion. Nevertheless, a considerable energy loss associated with the charging and discharging of the output capacitance (COSS) in these transistors severely limits their application at high switching frequencies. In this work we report the observation of unexpected resonances in GaN-on-Si HEMTs. These high-frequency resonances lead to considerable energy losses in fast charging and discharging of the COSS during switching transients. We propose a simple wafer-level measurement technique to evaluate such losses at the epitaxy level, prior to the transistor fabrication. Experimental results from this technique revealed that the Silicon substrate is the main origin of these losses. Such wafer-level evaluation of COSS losses opens opportunities to characterize and optimize epitaxies for future power devices, especially those operating at high switching frequencies. [ABSTRACT FROM AUTHOR]

Currently, the GaN-on-silicon high electron mobility transistor (HEMT) is a promising candidate to replace the Si Metal Oxide Semiconductor Field Effect Transistor (MOSFET) for high power electronics circuits. However, self-heating is still a challenging issue to be addressed, especially for high-current applications. In this paper, a GaN-on-Si HEMT with a diamond (Dia) heat spreader is proposed to suppress the self-heating effect. The performance of the proposed device is analyzed and compared with conventional GaN-on-Si and also GaN-on-SiC devices. The analysis was carried-out using technology computer aided design. The GaN-on-Si with diamond heat spreader suppresses the self-heating in the device and achieves higher saturation drain current than conventional GaN-on-Si. In addition, GaN-on-Si with Diamond heat spreader yields a higher transconductance and cut-off frequency than GaN-on-Si. This improved structure will provide a low cost device with enhanced thermal characteristics for higher power applications. [ABSTRACT FROM AUTHOR]

Device surface properties are critical for its performance such as channel electron density, leakage current, subthreshold swing (SS), and noise in gallium nitride high-electron-mobility transistors (HEMTs). In this article, the improved surface property of InAlN/GaN HEMTs with forming gas (FG, 5% H2, and 95% N2) annealing is demonstrated. X-ray photoelectron spectra (XPS) show that the number of Ga–O bonds decreases while that of the Ga–N bonds increases, an indication of the surface native oxide removal after FG annealing. Compared with N2 annealing, an increase of two-dimensional electron gas (2DEG) electron density with FG annealing is determined by both energy band simulation and capacitance–voltage measurement. Transmission line measurement (TLM) shows that N2 annealing offers a lower ohmic contact resistance (RC) while FG annealing features a lower sheet resistance (Rsheet). Herein, a FG/N2 two-step ohmic contact annealing is developed to achieve a SS of 110 mV/dec, a transconductance (gm) peak of 415 mS/mm, a record low drain-induced barrier lowing (DIBL) of 65 mV/V, and a record high power gain cutoff frequency (ƒmax) of 270 GHz on a 50-nm InAlN/GaN HEMT on Si. [ABSTRACT FROM AUTHOR]

Raman shift is one of the most important parameters in Raman spectroscopy and is theoretically calculated from the difference in the wavenumbers of excitation and Raman scattering. At present, there are no standard procedures available to reliably estimate the Raman shift and evaluate its uncertainty from experimental results. In this study, we reliably estimated the Raman shift and evaluated its uncertainty for a non‐doped crystalline Si substrate (NMIJ CRM5606‐a) using a He‐Ne laser and its plasma lines (Ne emission lines). The Raman scattering wavenumber of NMIJ CRM 5606‐a was estimated by the bracket calibration method using the wavenumbers of the closest Ne emission lines. The Raman shift was determined from the differences in the theoretical wavenumbers of a He‐Ne laser and the observed Raman scattering. To evaluate the combined standard uncertainty, we considered the uncertainty originating from the He‐Ne laser and the Ne emission lines, the repeatability of experimental results, inhomogeneity of measuring points and spectral dispersion. The estimated Raman shift was 520.45 cm−1 ± 0.28 cm−1 (coverage factor k = 2). The Raman shift was validated by the other estimated Raman shifts obtained with other two Raman spectrometers. [ABSTRACT FROM AUTHOR]

The properties of iodine-doped (211) CdTe layers grown on (211) Si substrates by metalorganic vapor-phase epitaxy at high substrate temperatures from 325°C to 450°C were studied. The growth rate of the doped layer increased with increasing substrate temperature before reaching a maximum value of 2.6 μm/h at 425°C, after which it decreased slightly. On the other hand, the room-temperature electron density showed a strong dependence on the Te/Cd precursor flow-rate ratios, where the electron density increased with a decreasing Te/Cd ratio. The highest electron density of 2.5×1018 cm−3 was obtained by growing the epilayer at a substrate temperature of 400°C and Te/Cd ratio of 0.05. This was considered to be due to decreased donor compensation at a small Te/Cd ratio. Good correspondence was observed between the results obtained from Hall measurements and photoluminescence measurements. [ABSTRACT FROM AUTHOR]

Rhombohedral La:BiFeO 3 films were successfully prepared on Si substrates by using Radio frequency magnetron sputtering method. The LaNiO 3 as buffer layer is beneficial for improving the quality of the film, reducing surface roughness, and getting rid of the impure phase. The Bi 0.9 La 0.1 FeO 3 /LaNiO 3 /Si film has the largest piezoelectric coefficient with d 33 reaching 4.76 pm/V, which is about 2.5 times larger than that of BiFeO 3 /LaNiO 3 /Si. The saturation magnetization and the MCD signal of BiFeO 3 films are significantly enhanced by doping La3+. The MCD ellipticity of La:BiFeO 3 film at 555 nm increase with the increase of La3+ concentration. Bi 0.7 La 0.3 FeO 3 /LaNiO 3 /Si film show strong magneto-optical effect with the high MCD ellipticity of 850 deg./cm, which is more than about 1.7 times larger than that of BiFeO 3 film. This film is expected to be developed into a new multifunctional material with multi-field coupling of electro-opt-magnetism. • Successful integration of magneto-optical film with Semiconductor Si substrates. • La3+ doping improved piezoelectric and magneto-optical properties of BiFeO 3 films. • LaNiO 3 as the buffer layer improves the quality of films and optical properties. [ABSTRACT FROM AUTHOR]

Visible light communications with InGaN-based light-emitting diodes (LEDs) grown on large-diameter (6-inch) and cost-effective Si (111) substrates are investigated experimentally. During epitaxial growth, the transition layers consisted of the step-graded AlGaN buffers incorporated with three low-temperature-grown (~900 °C) AlN interlayers on AlN/Si substrates that are used to compensate for thermally induced tensile stress and to maintain a reasonable crystalline quality of GaN-on-Si LEDs. Strong light absorption from Si can be prevented by fabricating a Si substrate-free InGaN LED with a composite metal coating of Al/Ag/Al multilayer, providing improved adhesive strength and reflectivity comparable to the unitary Ag film. In comparison with GaN-on-Si LEDs, stripping Si substrates combined with the use of a highly reflective bottom mirror (Al/Ag/Al multilayer) reflected a more intense emission pattern corresponding to a 2.2 times (@ 190 mA) increase in light output power in thin-film LEDs. In addition, a 1.8 times (@ 160 mA) increase in optical channel bandwidth is achieved by using thin-film LEDs as optical transmitters. A direct line-of-sight optical link using the proposed thin-film LEDs achieved data transmission rates of up to 100 Mb/s over a distance of 100 cm, indicating that the proposed LEDs have potential for use as optical transmitters in indoor visible light communications.

• The cut-off angle of Si substrate is conducive to deposition of Ge film. • The substrate temperature of magnetron sputtering determines the density and the surface morphology of deposited film. • The RTA treatment has optimum duration for the recrystallization of Ge film. • Ge (1 1 1) appears the preferred orientation in all crystal planes of Ge film. In the deposition progress of heterogeneous germanium thin film, a single crystalline silicon with suitable cut-off angle can reduce lattice mismatch between the film and substrate, and a certain substrate temperature can reduce thermal mismatch. The highly crystallized Ge thin films have been fabricated by magnetron sputtering and rapid thermal annealing (RTA) on substrates with cut-off angle, including Si (1 0 0), Si (1 0 0) misorients (1 1 0) 6° and 10°, Si (1 0 0) misorients (1 1 1) 8° monocrystalline wafers. Ge film grown on Si substrate with a cut-off angle of 8° at 450 °C has achieved the best preferred orientation of Ge (1 1 1), I Ge (1 1 1) /I Ge (2 2 0) average value is greater than 3 after RTA treatment at 800 °C for 150 s. Ge (1 1 1) has occupied a proportion of 69% in total diffraction intensity of all crystal plane. The mechanism of the Ge films crystallization on the substrate with different cut-off angels is also analyzed. [ABSTRACT FROM AUTHOR]

The Ga Si interdiffusion during (Al)GaN/AlN growth on Si substrate by plasma assisted molecular beam epitaxy (PA-MBE) is studied. The epilayers were grown using a combination of different III/V ratios for GaN and AlN layers. The columnar morphology of the nitrogen-rich (III/V < 1) AlN nucleation layer allows the migration of Ga metal into Si, leading to the interdiffusion. The presence of less Ga at the GaN/AlN interface and the two-step growth process of AlN with different column sizes on the top and bottom AlN completely eliminates the possibility of Ga Si interdiffusion. Alternatively, a thin silicon nitride as a nucleation layer for the growth of (Al) GaN layers was also found to prevent the Ga Si interdiffusion thereby circumventing the process of melt-back etching. • Evolution and prevention of Ga Si interdiffusion in (Al)GaN/AlN growth on Si by PAMBE • Ga Si interdiffusion leads to microcrystals and voids on the (Al)GaN surface. • Ga diffuses through the spaces between the AlN columns causing meltback etching of Si. • A combination of two-step grown AlN and GaN results in microcrystal-free surface. • SiN x as a nucleation layer acts as an effective barrier layer for Ga Si interdiffusion. [ABSTRACT FROM AUTHOR]

We have explored the role of growth temperature as well as Al/N flux ratio on the microstructural evolution of high quality AlN grown by Plasma Assisted Molecular Beam Epitaxy. During the transformation process of AlN, lowest full widths at half maximum value of 15 arcmin has been achieved corresponding to lowest screw dislocation density of 8.5 × 108 cm−2. The results determine that AlN films with such low dislocation density can be fruitful as a buffer layer for various III-Nitride structures along with several optoelectronic applications like laser diodes, vacuum UV photodetectors, etc. • Investigated the role of growth temperature & Al/N flux on AlN microstructures. • Realized the lowest FWHM value of 15 arcmin for AlN grown on Si (1 1 1) substrate. • Significantly reduced screw dislocations up to 8.5 × 108 cm−2. • Examined the interplay between temperature & N 2 flow for eliminating metallic Al. The morphological evolution of AlN microstructures by varying the growth temperature and Al/N flux ratio on Si (1 1 1) substrate via plasma-assisted molecular beam epitaxy has been investigated. The transformations in microstructures of AlN grown along the c-plane were explored as a function of N 2 -flow rate, growth temperature and Al-flux. The structural analysis carried out using high resolution X-ray diffraction reveals single crystalline quality with reduced full widths at half maximum value of 15 arcmin corresponding to a screw dislocation density of 8.5 × 108 cm−2. The topographical study of AlN grown by modulating growth conditions revealed an average surface roughness of 6.9 nm. It was exemplified that interplay between higher growth temperature and nitrogen flow rate is desired to prevent condensation of metallic Al on the surface. Also, the AlN pertaining less screw dislocation density leads to lower dark current which can be fruitful for various optoelectronic applications like vacuum-UV photodetectors. [ABSTRACT FROM AUTHOR]

Abstract GaN-based light-emitting diodes (LEDs) on Si substrates are promising to replace conventional lamps due to the advantages of energy-saving and low-cost of LEDs grown on large-size Si substrates. However, high-density dislocations and cracks of GaN epitaxial films are usually formed that limit the further development and application of GaN-based LEDs. To circumvent the issues, the step-graded AlGaN buffer layers are carefully designed to grow GaN epitaxial films on Si substrates. The mechanisms of dislocations and stresses for GaN epitaxial films controlled by step-graded AlGaN buffer layers are also investigated by analyzing dislocations evolution and stresses relaxation at the hetero-interfaces. Afterwards, 3.0 μm-thick high-quality GaN epitaxial films grown on Si substrates have been obtained, and high-quality GaN-based LED wafers are obtained accordingly with small full-width at half-maximums (FWHMs) for GaN(0002) and GaN(10–12) X-ray rocking curves of 272 and 297 arcsec, respectively. The corresponding vertical-structure LED chips reveal high-performance with a high light output power of 592 mW and a small working voltage of 2.77 V @ 456 nm, at a current of 350 mA. This work provides an effective approach for the growth of high-quality crack-free GaN epitaxial films on Si substrates for the fabrication of high-performance GaN-based devices. Graphical abstract Image 1 Highlights • High-quality GaN epitaxial films have been grown on Si substrates by designing the step-graded AlGaN buffer layers. • The mechanisms of stress and dislocation density of GaN epitaxial films on 4-inch Si substrates have been revealed. • High-performance vertical-structure LEDs with high light output power of 592 mW @350 mA have been obtained. [ABSTRACT FROM AUTHOR]

Abstract The optical quality enhancement of a GaAs template grown on Silicon substrate using InGaAs/GaAs Dislocation Filters (DFs) combined with an annealing step have been assessed optically using Photoluminescence (PL) of embedded InAs/InGaAs QDs within a GaAs matrix. An annealing temperature after the growth of the DFs of 690 °C was shown to be optimum, giving an enhanced PL emission from the embedded InAs QDs in terms of intensity and Full Width at Half Maximum (FWHM). InAs quantum dots capped with GaAsSb grown at different temperatures were grown on the optimized GaAs template on Si. The prepared samples were characterized by PL, Atomic Force Microscopy (AFM), excitation power and dependent PL at 77 K and 300 K. At 77 K, the InAs/GaAsSb grown at 484 °C showed a type II band alignment with an emission wavelength of 1297 nm, which is shorter than the emission obtained from the reference sample, where the GaAsSb-capped dots were grown on GaAs (1357 nm). By reducing the GaAsSb capping layer growth temperatures to 465 °C and 450 °C, the wavelength at 77 K was extended to 1375 nm and 1480 nm respectively, resulting from an increased Sb content in the capping layer. At 300 K, a long wavelength emission of 1623 nm have been achieved. Highlights • GaAs template optimization on Si using dislocation filters and in-situ annealing. • Growth of InAs/GaAsSb QDs on the prepared GaAs template. • The InAs/GaAsSb QDs grown at 484 °C showed a type II emission with λ = 1297 nm at 77 K. • Extension of λ to 1375 nm and 1480 nm at 77 K for GaAsSb grown at 465 °C and 450 °C. • Emission wavelength of 1623 nm from InAs/GaAsSb QDs grown on Si substrate at 300 K. [ABSTRACT FROM AUTHOR]

Abstract To develop Aluminum Antimonide (AlSb) -based optoelectronic devices on Si substrates, AlSb films were investigated for a good crystalline quality and suitable optical and electrical properties. Under an optimized growth condition by RF-magnetron sputtering technique, the AlSb films were grown at a sputtering power of 250 W and a pressure of 0.01 mbar in argon atmosphere and a precursor Al:Sb ratio of about 88:12. The undoped AlSb films were found to have a cubic crystal structure with (111) preferred orientation and a lattice constant of 5.9985 Å under compressive strain. For the doped AlSb samples with optimized doping contents, the AlSb:Si and AlSb:Cu films with higher compressive strain were found to have a smaller lattice constant of 5.9588 Å and 5.9667 Å, respectively. Raman spectroscopy indicated strain states and lower crystalline quality induced by doping. The optical properties, analyzed by UV–Vis spectrophotometry, showed that the undoped AlSb film was transparent to IR at around 850 nm, where the doped films were transparent to IR at longer wavelengths. To evaluate the electrical properties of the AlSb films, n-type AlSb:Cu and p-type AlSb:Si films were characterized by Hall-Effect measurements. To develop AlSb-based optoelectronic devices, a PIN diode structure was grown on Si substrate. The smooth interfaces between the AlSb layers and with Si substrate were confirmed by cross-sectional TEM micrographs. Finally, I-V measurements showed diode characteristics with a turn-on voltage of about + 1.5 V for forward bias and −0.5 V for reverse bias. In summary, the AlSb-based diode structure on Si substrate had been successfully fabricated by optimized sputtering deposition. This is promising for future development of the AlSb-based optoelectronic devices. [ABSTRACT FROM AUTHOR]

A crack-free GaN film grown on 4-inch Si (111) substrate is proposed using two-step growth methods simply controlled by both III/V ratio and pressure. Two-step growth process is found to be effective in compensating the strong tensile stress in the GaN layer grown on Si substrate. The high-resolution X-ray diffraction (XRD) rocking curves of (002) and (102) planes for the GaN epitaxial layer with two-step growth method are 317 and 432 arcsec, while the corresponding values for the reference sample without two-step growth method are 550 and 1207 arcsec, respectively. The reduced threading dislocation of GaN film with two-step growth method is obtained to be ~2 × 108/cm2, which is attributed to effectively annihilate and bend threading dislocation.

[Display omitted] • Au nanowires grow by thermal evaporation on the Si substrate irradiated with Ar ion. • Nanowires are well arranged in specific locations by limiting the region irradiated. • The length and diameter of the nanowires can be controlled by tuning the irradiation area. • The structure under the Au nanowire is revealed by cross-sectional microscopic analysis. • A growth model of the Au nanowire by surface migration of Au adatoms was developed. This study aims to clarify the mechanism of site-selective Au-nanowire (NW) growth on Si substrates irradiated with Ar ions. Au NWs are grown by Au evaporation at specific regions in the boundary zones between the ion-irradiated and unirradiated areas of Si substrates. The NW growth area are restricted by placing a grid mesh with a certain hole size within the boundary zone to limit the irradiation area. The length and diameter of the NWs can be controlled by controlling the hole size. Cross-sectional microscopic analyses reveal the presence of a thin Si-oxide layer as well as an Au–Si buried layer beneath the NWs. A site-selective Au NW growth model is developed by modifying the already-existence model. By fitting the Au NW length calculated using our model to the experimental data, the surface diffusion length of Au adatoms (λ s) is estimated to be approximately 7 μm, close to the radius of the irradiated area R w (6 μm). This validates our model that assumes that the NWs are grown at the bottom from the Au adatoms migrating onto the substrate. The Au-NW growth mechanism is discussed along with the role of the oxide layer and surface diffusion of Au adatoms. [ABSTRACT FROM AUTHOR]

This paper presents a simple and optimized metal organic chemical vapor deposition (MOCVD) protocol for the deposition of perovskite BiFeO3 films on silicon-based substrates, in order to move toward the next generation of lead-free hybrid energy harvesters. A bi-metal mixture that is composed of Bi(phenyl)3, and Fe(tmhd)3 has been used as a precursor source. BiFeO3 films have been grown by MOCVD on IrO2/Si substrates, in which the conductive IrO2 functions as a bottom electrode and a buffer layer. BiFeO3 films have been analyzed by X-ray diffraction (XRD) for structural characterization and by field-emission scanning electron microscopy (FE-SEM) coupled with energy dispersive X-ray (EDX) analysis for the morphological and chemical characterizations, respectively. These studies have shown that the deposited films are polycrystalline, pure BiFeO3 phase highly homogenous in morphology and composition all over the entire substrate surface. Piezoelectric force microscopy (PFM) and Piezoelectric Force Spectroscopy (PFS) checked the piezoelectric and ferroelectric properties of the film.

This paper reports on an initial assessment of the direct growth of In(Ga)As/GaAs quantum dots (QDs) solar cells on nanostructured surface Si substrate by molecular beam epitaxy (MBE). The effect of inserting 40 InAs/InGaAs/GaAs QDs layers in the intrinsic region of the heterojunction pin-GaAs/n+-Si was evaluated using photocurrent spectroscopy in comparison with pin-GaAs/n+-Si and pin-GaAs/GaAs without QDs. The results reveal the clear contribution of the QDs layers to the improvement of the spectral response up to 1200 nm. The novel structure has been studied by X ray diffraction (XRD), photoluminescence spectroscopy (PL) and transmission electron microscopy (TEM). These results provide considerable insights into low cost III-V material-based solar cells.

A comparative study on characteristics and performance of optical ring resonator architectures, i.e. circular, racetrack, and triangular‐shaped optical resonators, have been carried out here. Constituent material used for designing these resonators is an silicon on insulator wafer consisting of thin silicon (Si) layer on silica (SiO2) layer carried on a thick Si substrate having group index of 2.379. All the resonators are so designed that all provide equal free spectral range (FSR) of 25.2 THz. All these double‐ring architectures have been analysed using delay line signal processing technique in z‐domain and Mason's gain formula. FSR expansion has been achieved employing the Vernier principle. Various performance defining parameters have been also investigated. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, because of increased carbon dioxide emissions problem, the air pollution has been attracting attention. For example, the exhaust fumes produce nitrogen oxide and sulfur oxide. Therefore, these gases should be detected and measured. In this paper, we propose a novel moisture‐insensitive sensor consisting of a comb‐shaped electrode on a Si substrate. We also suggest a new measurement method, using complex impedances, for distinguishing between NO2 and SO2 at low concentrations. It is shown that propose oxidizing‐gas sensor, fabricated on a Si substrate, is moisture‐insensitive for humidity of 40% to 80%. Furthermore, we determine that it is possible to measure mixed gases in the range of 0.1–0.9 ppm for nitrogen dioxide and 0.6‐1.4 ppm for sulfur dioxide owing to the difference in the complex‐impedance change pattern. [ABSTRACT FROM AUTHOR]

A combined buffer layer growth process was developed to grow crack-free GaN layers on 8-inch Si(111) wafers and so light-emitting diodes (LEDs). The combined buffer layer consisted of 2 nm-thick low-temperature (LT, 850 °C)-AlN, 8 nm-thick graded-temperature AlN, and 200 nm-thick high-temperature (HT, 1100 °C)-AlN layers. The X-ray diffraction (XRD) results showed that the LT-HT-AlN buffer layer exhibited better crystal quality than the HT-AlN buffer layer. The atomic force microscopy (AFM) images revealed that compared to the LT-HT-AlN buffer layer, the HT-AlN buffer layer had a rough surface with numerous bright spots, which correspond to N-polar AlN hillocks. Scanning electron microscopy (SEM) results showed many pits in the HT-AlN buffer layer. Transmission electron microscopy (TEM) results showed that the HT-AlN buffer layer contained about 1.3 nm-thick amorphous Si x N y layer at the interface, while the LT-HT-AlN buffer layer showed a relatively smooth interface. It was further shown that using the LT-HT-AlN buffer layer, high-quality crack-free n -GaN layers (2.5 μm-thick) were grown on the 8-inch Si(111) substrate, which was confirmed by the XRD and cathodoluminescence results. Subsequently, packaged vertical LEDs (chip size: 1400 × 1400 μm 2 ) grown on the LT-HT-AlN buffer layers showed higher light output power and chip yield than LEDs with the HT-AlN buffer layer. [ABSTRACT FROM AUTHOR]

In this letter, InAlN/GaN high electron mobility transistors (HEMTs) with 40–200 nm rectangular gates and 300–700 nm source-to-drain distances were fabricated on Si substrates. The device with 40-nm gate and 300-nm source-to-drain distance exhibited a high drain current of 2.66 A/mm, a transconductance ( g m ) of 438 mS/mm, and a high current gain cutoff frequency ( f T ) of 250 GHz. To the best of our knowledge, this is the highest f T value reported so far for GaN-based transistors on Si. An effective electron velocity of 1.1 \times 10^7 cm/s was extracted, which is comparable with those reported for InAlN/GaN HEMTs on SiC. These excellent results indicate that GaN HEMTs on Si have a great potential for low-cost emerging mm-Wave applications. [ABSTRACT FROM AUTHOR]

ε-Ga2O3 (002) thin films were successfully grown on Si (100) substrate by metalorganic chemical vapor deposition (MOCVD). The crystal structure, chemical composition, and surface morphology of ε-Ga2O3 (002) thin films were analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). The lattice mismatch between Si and ε-Ga2O3 was effectively reduced by inserting Molybdenum (Mo) buffer layer. Quasi-vertical ε-Ga2O3 Schottky barrier diode (SBD) solar-blind photodetectors grown on Si (100) substrate with the Mo buffer layer were fabricated and characterized. The device has a photo-to-dark current ratio (PDCR) of 1.57 × 103, a responsivity (R) of 243.14 A·W-1, a detectivity (D*) of 1.83 × 1017 Jones (cm·Hz1/2 W−1), and an excellent response time due to improved crystal quality and the vertical device structure. This work provides an important reference for the heteroepitaxial growth of ε-Ga2O3 on Si, which is beneficial to the development of low-cost, high-performance ε-Ga2O3 optoelectronic and power electronic devices. • This work proves that the crystal quality of Mo films increases with the increase of annealing temperature. • High quality gallium oxide crystal thin films have been successfully epitaxial grown on Si. • The epitaxial relationship between Mo and ε-Ga 2 O 3 was demonstrated to be consistent with ε-Ga 2 O 3 (002)//Mo (110) and ε-Ga 2 O 3 (101)//Mo (211). • ε-Ga 2 O 3 photodetectors with a Schottky barrier diode (SBD) structure have been fabricated and excellent optical performance were obtained. [ABSTRACT FROM AUTHOR]