We are reporting on stress engineering utilizing AlN/GaN superlattices (SLs) for epitaxy of GaN layers on 200 mm silicon substrates carried out in Veeco's Propel™ rotating disk, single wafer metal organic chemical vapor deposition (MOCVD) reactor. The Turbodisc® reactor is designed to have homogeneous alkyl/hydride flow distribution and uniform temperature profile, which translate into excellent uniformity and concentric symmetry in epilayer thickness and alloy composition. This feature results in uniform and controllable stress in epilayers across large-size substrates. Crack-free 2 μm GaN layers were grown on 200 mm Si using uniformly strained AlN/GaN SLs with periods of 3–5 and 10–30 nm, respectively. Compressive and tensile stress can be precisely adjusted by changing the thickness of the AlN and GaN layers in the SLs, resulting in controllable wafer curvature/bow after cool down. For a fixed period thickness structure, the effects of growth conditions, such as growth rate of GaN, AlN V/III ratio, and growth temperature, on wafer stress were investigated.

This review focuses on in situ functionalization of gallium nitride (GaN) with different adsorbates in the presence of an etchant. The low-temperature aqueous nature of this process provides a safe, environmentally friendly technique for tailoring the semiconductor's properties for various applications. Surface binding to GaN relies on a native oxide layer or direct attachment to the metal center present on the etched surface. The specifics of the binding mechanism are based on the functional groups present on the adsorbate. The effects of the GaN surface polarity and quality on the modification approach are analyzed. The review summarizes the alteration of GaN properties after the in situ treatment. Quantitative data until now have shown changes in morphological, surface chemical, optical, electronic, and aqueous stability properties. The review concludes with a short outlook on future studies associated with this surface modification approach.

AlGaN-based quantum well (QW) heterostructures grown by plasma-assisted molecular beam epitaxy on c-Al2O3 substrates have been studied. The high-temperature (785 °C) synthesis of AlN buffer layer nucleated by a migration-enhanced epitaxy and including several ultrathin GaN interlayers was the optimum approach for lowering the threading dislocations density down to 108–109 cm−2. High-angle annular dark-field scanning transmission electron microscopy (HAADF STEM) has revealed the step-like roughness of the AlN/Al2O3 interface. Also, the formation of Al-rich barriers induced by temperature-modulated epitaxy and the spontaneous compositional disordering have been found in the AlxGa1−xN (x > 0.6) barrier layers. The origin of these phenomena and their influence on parameters of the mid-UV stimulated emission observed in the QW heterostructures were discussed. The fine structure of the QWs formed by a submonolayer digital alloying technique has been displayed by HAADF STEM, and optical properties of the QW structures were studied by temperature- and time-dependent photoluminescence spectroscopy.

A fast and nondestructive method for polarity determination of wurtzite GaN crystals based on x-ray photoelectron diffraction (XPD) has been demonstrated. Photoelectron emission from N 1s core level excited by Mg Kα source was found sufficient for the polarity determination of GaN crystals. XPD polar plots from polar GaN {0001} and semipolar GaN$\{ 10\bar 11\}$, $\left\{ {20\bar 21} \right\}$, $\left\{ {11\bar 22} \right\}$ crystals have been analyzed. Due to dominant electron forward scattering along N–Ga directions, photoelectron intensities either increase or decrease within a relatively narrow emission polar angle range. The slopes of polar plots are found noticeably different in the polar angle range of 20°–25° for (0001) or $\left( {000\bar 1} \right)$ crystals, respectively. The semipolar GaN substrates can be divided into two groups, depending on whether m-plane or a-plane is perpendicular to the semipolar surface. It was found that the slopes of the polar plots are different in the angular range of 20°–27° for semipolar GaN$\left\{ {10\bar 11} \right\}$, 10°–22° for GaN$\left\{ {20\bar 21} \right\}$ substrates, while for the GaN$\left\{ {11\bar 22} \right\}$ semipolar planes, the slopes are different in the range of 0°–15° with respect to the surface normal.

A quantitative analysis of In concentration in InGaN/GaN multiquantum wells in light-emitting diodes was carried out using high-resolution transmission electron microscopy (HRTEM) and high-angle annual dark-field scanning TEM (HAADF-STEM). The In composition in InGaN was evaluated by the precise measurement of c-lattice parameters in the HRTEM micrographs, which increase with increasing In composition. The reliability of the results was confirmed by high-resolution x-ray diffraction measurements and Rutherford backscattering spectrometry. Quantitative In compositions can, therefore, be determined using HRTEM. We tried to determine the quantitative In compositions in InGaN by analyzing the intensity profiles of the HAADF-STEM images. However, several problems were encountered, such as differences in the thickness of the region observed, carbon contamination, and ion beam damage during specimen preparation. Therefore, relative differences in composition were observed in the HAADF-STEM images.

In situ curvature measurements were used to compare the stress evolution of GaN films grown directly on 6H-SiC via a two-step temperature growth to films grown with an AlN buffer layer. The two-step temperature growth consisted of an initial low-temperature and a main high-temperature GaN layer. In the case of GaN grown directly on 6H-SiC, the high-temperature layer initiated growth under compressive stress which transitioned to tensile stress. Films grown directly on 6H-SiC exhibited a reduction in the threading dislocation (TD) density and an improvement in the surface roughness compared to growth on the AlN buffer layer. Furthermore, transmission electron microscopy of the GaN grown directly on 6H-SiC revealed predominant (a + c)-type TD along with basal plane stacking faults and $\left\{ {11\bar 20} \right\}$ prismatic stacking faults. Channeling cracks were observed in the GaN film when the AlN buffer layer was not utilized. This was attributed to tensile stress induced from the thermal expansion coefficient mismatch.

This work focused on the modification of milled GaN powder. Successful attachment of a porphyrin derivative to a GaN powder was performed via in situ functionalization in the presence of phosphoric acid. The GaN powder was imaged using scanning electron microscopy and was found to be heterogeneous in nature, adopting no consistent geometry in the aggregates. The aqueous stability of the porphyrin used was observed in deionized water and a solution of phosphoric acid using ultraviolet–visible spectroscopy. Surface chemistry was characterized with x-ray photoelectron spectroscopy and infrared spectroscopy, which identified evidence of successful functionalization through the presence of characteristic peaks. The interface stability of the covalent bond between GaN and porphyrin was evaluated using fluorescence spectroscopy and demonstrated no leaching of dye in water solutions for 20 days.

Ca0.98Eu0.02Al1−4δ/3Si1+δN3 (δ = 0–0.36) red-emitting phosphors were prepared by carbothermal reduction and nitridation method with stable and inexpensive CaCO3 as Ca source. Optimal nominal composition was obtained at δ = 0.18, showing intense emission peaked at 625 nm and high external quantum efficiency of 71%. The emission wave length could be successfully tuned from 630 to 606 nm with increasing δ value. Ca0.98Eu0.02Al1−4δ/3Si1+δN3 phosphors provided two coordinated environments for Eu2+ ions, resulting in two fitted Gaussian peaks. Energy transfer from Eu2+ sites in Si-rich environments to those in Si/Al-equivalent modes has been confirmed by analysis of the decay curve of each peak. The decay behaviors suggested that energy transfer effect slowed with higher δ value. Finally, warm white light was created by combining as-prepared red-emitting Ca0.98Eu0.02Al0.76Si1.18N3 and yellow-emitting YAG:Ce3+ phosphors with a blue-emitting chip, exhibiting a color rendering index Ra of 91 at a low correlated color temperature of 3500 K with a luminous efficiency of 79 lm/W.

Recent efforts have demonstrated enhanced tailoring of material functionality with mixed anion materials, yet exploratory research with mixed anion chemistries is limited by the sensitivity of these materials to synthesis conditions. Synthesis of a particular metal oxynitride compound by traditional reactive annealing requires specific, limited ranges of both oxygen and nitrogen chemical potentials to establish equilibrium between the solid-state material and a reactive atmosphere. Using Ta–O–N as an example system, we describe a combination of reactive sputter deposition and rapid thermal processing (RTP) for synthesis of mixed anion inorganic materials. Heuristic optimization of reactive gas pressures to attain a desired anion stoichiometry is discussed, and the ability of RTP to enable amorphous to crystalline transitions without preferential anion loss is demonstrated through the controlled synthesis of nitride, oxide, and oxynitride phases.

Self-energy correction density functional theory local density approximation–1/2 (LDA-1/2) method was successfully applied to predict the electronic structure and optical properties of the N-doped, Ti-vacant Ti3−δO4N oxynitride [G. Hyett et al., J. Am. Chem. Soc.129, 15541–15548 (2007)], which was shown experimentally to be more photocatalytic than titania. The procedure takes into consideration of the two possible types of Ti vacancies (with different numbers of nitrogen and oxygen neighbors) and their formation energies, according to the experimental data on fractional occupancies, with potential effects on the electronic structure and photocatalyst mechanisms analyzed. Different defective model structures were calculated for optimal final configuration, whose optical calculations revealed massive damping in infrared spectrum, while transparency in green region. The band gap determined by our methodology is 2.5 eV, in close agreement to the experimental value of 2.6(1) eV. Results presented in this work represent the first report of an electronic structure modeling of Ti3−δO4N, which is a starting point to help provide an understanding of its photocatalytic activity.

Lithium thio-phosphorus oxynitride glasses, LiPOSN, have been prepared by mechanical milling process from the mixture of Li2S and LiPON glass. The anionic substitution of oxygen by sulphur and nitrogen in the phosphate glass structure has been confirmed by 1D 31P solid state nuclear magnetic resonance and x-ray photoelectron spectroscopy. The study of thermal and electrical properties reveals a decrease in the glass transition temperature, likely due to the depolymerization of glass network by the decrease of bridging oxygens and sulphurs, along with a sharp increase in the ionic conductivity when lithium sulphide is incorporated into the oxynitride glasses. The improvement of chemical durability by the introduction of nitrogen, together with the increase in ionic conductivity up to values closed to the value of commercial LiPON thin film electrolyte, suggests that these LiPOSN glasses could be good candidates as solid electrolytes for lithium microbatteries.

A series of (HfN)1−x(TaN)x, ceramics with x representing the starting powder blend compositions of 0.0, 18.8, 28.1, and 46.7 at.%, have been fabricated by vacuum plasma spraying. During the plasma spraying, the mixture lost approximately 25 at.% nitrogen facilitating the precipitation of metallic and metal-rich nitride phases. These specimens underwent static air oxidation exposure up to 1700 °C. In general, it was found that the addition of tantalum nitrides to the hafnium nitrides resulted in poorer oxidation behavior. However, the 18.8 at.% specimen deviated from this trend and had the lowest observed mass change. This specimen formed a dark-colored oxide scale, indexed as Hf6Ta2O17, which acted as a passivation layer. Within the scale, hafnium oxynitride phases were observed. A transformation pathway in forming these rhombohedral oxynitride phases is proposed by the filling in of oxygen in the light element interstitial locations of the rhombohedral ε-Hf3N2 and ζ-Hf4N3 structures.

Carbon dioxide (CO2) capture is regarded as one of the biggest challenges of the 21st century; therefore, intense research effort has been dedicated in the area of developing new materials for efficient CO2 capture. Here, we report high CO2 capture capacity in the low region of applied CO2 pressures observed with ultramicroporous silicon nitride-based material. The latter is synthesized by a facile one-step NH3-assisted thermolysis of a polysilazane. Our newly developed material for CO2 capture has the following outstanding properties: (i) one of the highest CO2 capture capacities per surface area of micropores, with a CO2 uptake of 2.35 mmol g−1 at 273 K and 1 bar (ii) a low isosteric heat of adsorption (27.6 kJ mol−1), which is independent from the fractional surface coverage of CO2. Furthermore, we demonstrate that the pore size plays a crucial role in elevating the CO2 adsorption capacity, surpassing the effect of Brunauer–Emmett–Teller specific surface area.

This work studies the nitridation of Ta by laser irradiation by means of x-ray photoelectron spectroscopy. The study has been carried out under “in situ” conditions by controlling the nitrogen partial pressure, the presence of traces of oxygen, and the irradiance of the laser. It is found that a thin layer of Ta2O5 is directly obtained when irradiating in the presence of oxygen, while a Ta3N5 surface compound and some minor contributions of nonstoichiometric phases are formed in the presence of nitrogen. For O2:N2 mixtures at 0.1 Pa, preferential nitride formation occurs up to a ratio of 1:4, while Ta2O5 starts to be predominant for ratios above this value. The air stability of the tantalum nitride layer formed by laser irradiation and the surface topography of the irradiated metal are also studied. The possible factors determining this behavior are discussed.