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High-electron-mobility transistors (HEMTs) based on AlGaN/GaN epitaxial heterostructures are a promising element base for the fabrication of high voltage electronic devices of the next generation. This is caused by both the high mobility of charge carriers in the transistor channel and the high electric strength of the material, which makes it possible to attain high breakdown voltages. For use in high-power switches, normally off-mode GaN transistors operating under enhancement conditions are required. To fabricate normally off GaN transistors, one most frequently uses a subgate region based on magnesium-doped p-GaN. However, optimization of the p-GaN epitaxial-layer thickness and the doping level makes it possible to attain a threshold voltage of GaN transistors close to V = +2 V. In this study, it is shown that the use of low temperature treatment in an atomic hydrogen flow for the p-GaN-based subgate region before the deposition of gate-metallization layers makes it possible to increase the transistor threshold voltage to V = +3.5 V. The effects under observation can be caused by the formation of a dipole layer on the p-GaN surface induced by the effect of atomic hydrogen. The heat treatment of hydrogen-treated GaN transistors in a nitrogen environment at a temperature of T = 250°C for 12 h reveals no degradation of the transistor's electrical parameters, which can be caused by the formation of a thermally stable dipole layer at the metal/ p-GaN interface as a result of hydrogenation. [ABSTRACT FROM AUTHOR]

The composition and structure of silicon surface layers subjected to combined gallium and nitrogen ion implantation with subsequent annealing have been studied by the X-ray photoelectron spectroscopy, Rutherford backscattering, electron spin resonance, Raman spectroscopy, and transmission electron microscopy techniques. A slight redistribution of the implanted atoms before annealing and their substantial migration towards the surface during annealing depending on the sequence of implantations are observed. It is found that about 2% of atoms of the implanted layer are replaced with gallium bonded to nitrogen; however, it is impossible to detect the gallium-nitride phase. At the same time, gallium-enriched inclusions containing ∼25 at % of gallium are detected as candidates for the further synthesis of gallium-nitride inclusions. [ABSTRACT FROM AUTHOR]

The aim of this work is to demonstrate the fundamental possibility of Si-doped GaN nanowires growth on the buffer layer of silicon carbide on silicon substrate and to investigate the optical characteristics of this structures. [ABSTRACT FROM AUTHOR]

High-quality nonpolar m-plane GaN-based light-emitting diode (LED) wafers on LiGaO(100) substrates have been grown in this work by the combination of pulsed laser deposition and molecular beam epitaxy technologies. This work systemically studies the crystalline quality, surface morphology, as well as optoelectronic properties of as-grown nonpolar m-plane GaN-based LED wafers. The as-grown nonpolar m-plane GaN-based LED wafers on LiGaO(100) substrates show good structural properties with estimated dislocation density ∼10 cm and abrupt InGaN/GaN interfaces. A photoluminescence peak at approximately 446 nm with full-width at half-maximum (FWHM) of 21.2 nm is identified at room temperature. A strong electroluminescence (EL) peak observed at 446 nm with FWHM of 20.7 nm is obtained at an injection current of 20 mA. Furthermore, there is a slight blue shift in the EL emission wavelength with increase in the injection current, while the EL FWHM can be kept stable thanks to the absence of the quantum confined Stark effect. This study of high-quality nonpolar m-plane GaN-based LEDs is of paramount importance for future application of high-efficiency GaN-based devices. [ABSTRACT FROM AUTHOR]

Intrinsic and extrinsic gallium nitride (GaN) nanostructures, due to their size tunable photo-physical and photo-chemical behavior, have attracted great interest for the fabrication of various smart optoelectronic devices. In the present paper, GaCoN (0 ≤ x ≤ 0.1) nanocrystals have been synthesized by facile solvothermal method. Crystallographic characterization of synthesized materials has been done using powder X-ray diffraction technique. Recorded diffraction patterns reveal the formation of wurtzite (hexagonal) structured GaN nanocrystals. Electron microscopic studies have been carried for the detailed topographical and morphological analyses of synthesized nanomaterials. Recorded electron micrographs indicate the formation of nearly mono-disperse nanoparticles having average size ~4 nm. Spectroscopic studies like energy dispersive X-ray spectroscopy, UV-visible absorption, Fourier transform infra-red spectroscopy, X-ray photoelectron spectroscopy and steady state energy resolved and time resolved photoluminescence spectroscopy studies have been opted for the investigation of quantitative, qualitative and optical behavior of synthesized nanomaterials. [ABSTRACT FROM AUTHOR]

Recently, wide band-gap III-Nirtride (III-N) materials and its alloys have attracted much research due to its unique properties and diverse field of applications. In the present study, GaN with various concentration of iron (Fe) in the range 0-5 at% nanostructures were prepared by facile solution process using (Ga(NO)·9HO), iron (III) chloride hexahydrate (FeCl·6HO) at mild temperature for the first time. The microstructure was analyzed by means of X-ray diffraction and atomic force microscopy. The detailed studies demonstrate that the as-synthesized nanoparticles are well crystallined GaN with a hexagonal wurtzite structure and having the average size of 31 nm in diameter. The optical properties of as the prepared GaN are investigated for Fe doping concentrations ranging from 0.1 to 5 at%. The optical band gap value increases with increasing Fe concentration. These results suggest that the Fe doped-GaN is a promising candidate for optoelectronics and spintronics devices. [ABSTRACT FROM AUTHOR]

We report improvement of improvement effectiveness of the light extraction efficiency of 10 W operated InGaN-based vertical light-emitting diodes via n-GaN surface roughening, using a commercial photoresist (PR) developer as an etching solution, which was compared with a conventional KOH-based solution. With the conventional KOH-based solution for n-GaN surface roughening, although both the depth and density of the etch pyramid initially increased with etching time, the depth eventually decreased and the density also decreased gradually, resulting in degradation in improvement effectiveness of extraction efficiency. Using the commercial PR developer for etching, however, after an initial increase in both the depth of the etch pyramid and its density, the depth and density were maintained without degradation, confirming the improvement in improvement effectiveness of extraction efficiency as well as the improvement in run to run fabrication uniformity. This may be due that with developer the GaN surface is etched only along the dislocation and is not etched over the non-defect region even as etching time goes on. [ABSTRACT FROM AUTHOR]

Hydride vapor phase epitaxy (HVPE) is used for the growth of low-defect GaN. We have grown undoped films on sapphire and investigated them using steady-state and time-resolved photoluminescence (PL). One of the dominant PL bands in high-quality GaN grown by HVPE is the green luminescence (GL) band with a maximum at 2.4 eV. This PL band can be easily recognized in time-resolved PL measurements due to its exponential decay even at low temperatures (<50 K), with a characteristic lifetime of 1-2 μs. As the temperature increases from 70 K to 280 K, the PL lifetime for the GL band increases by an order of magnitude. This unusual phenomenon can be explained on the assumption that the electron-capture coefficient for the GL-related defect decreases with temperature as T. [ABSTRACT FROM AUTHOR]

Helical gallium nitride nanowires were synthesized by chemical vapor deposition using a Pt catalyst. The prepared helical GaN nanowires with a single-crystalline hexagonal wurtzite structure have a coil diameter of 150-280 nm and lengths of up to tens of micrometers. The helical GaN nanowires have six equivalent 〈0 $$ \bar{1} $$ 11〉 growth directions along the [0001] axis. Field emission measurements show that helical GaN nanowire sheets possess excellent field emission properties, with a low turn-on field of ~4.5 V/ μm and a high field enhancement factor of ~2,751. It is believed that this material's excellent electron emission behavior can be attributed to its unique three-dimensional spiral structure. The growth mechanism of helical GaN nanowires has also been analyzed. [ABSTRACT FROM AUTHOR]

We examine the potentialities of heterosegregation processes in the synthesis of surface phases, as exemplified by the preparation of oriented GaN on single-crystal GaAs. A new phase has been obtained for the first time by reacting liquid gallium resulting from surface autosegregation on gallium arsenide with nitrogen gas at temperatures from 970 to 1050°C. The nanomorphology, elemental composition, and phase composition of the surface GaN layer produced by surface reactions have been assessed by high-resolution scanning electron microscopy, digital optical microscopy, and X-ray microanalysis. [ABSTRACT FROM AUTHOR]

Gallium nitride materials are at the forefront of nanoelectronic research due to their importance for UV optoelectronics. In this contribution, we present a facile and well-controlled synthesis of GaN nanodisks by rapid thermal ammonolysis of complex gallium fluoride precursor. We observed the formation of GaN nanodisks in 150 s at 800 °C. The structural properties of GaN were investigated by X-ray diffraction, Raman spectroscopy, and micro-photoluminescence. The morphology of GaN was investigated by scanning electron microscopy and the magnetic properties by superconducting quantum interference device (SQUID) techniques. The morphology of nanodisks was strongly influenced by the temperature of synthesis. The structure characterization shows a high concentration of defects related mainly to the vacancies of N and Ga. The magnetic measurement by SQUID shows paramagnetic behavior induced by structure defects. These findings have a strong implication on the construction of modern optoelectronic nanodevices. [ABSTRACT FROM AUTHOR]