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We studied the growth technique for the dislocation reduction in a-plane GaN grown by metal organic chemical vapour deposition (MOCVD) using AlInN buffer layer, high temperature atomic layer epitaxy, and trenched r-sapphire technique. By using these techniques, the crystal quality was much improved. We also fabricated blue light emitting diodes (LEDs) on a-plane GaN film over r-sapphire substrate and on a-plane bulk GaN substrate. The electroluminescence (EL) characteristics of the LED samples were examined, and we found that the EL near field pattern from homo-epitaxially grown a-GaN based LED was spatially uniform, although the pattern from the LED on r-sapphire substrate was not uniform. The output power at the wavelength of 430nm was 0.72mW at the 20mA injection current for the sample on a-plane bulk GaN. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigated the effect of a middle temperature intermediate layer (MTIL) of AlGaN and A1N/AlGaN super lattice structure (SLS) on the crystal quality of AlGaN epilayers grown by low-pressure metalorganic chemical vapor deposition (LP-MOCVD). MTIL-Al 0-17 Ga 0.83 N layers could enhance the lateral growth area at 950 °C, and the dislocations made dislocation loop. The full-width at half-maximum from (1012) X-ray rocking curve peak of HT-Al 0.17 Ga 0.83 N epilayers grown on MTIL decreased from 1220 to 525 arcsec. The dislocation density evaluated by atomic force microscopy density decreased from 1.0 x 10 10 to 1.3 x 10 9 cm -2 , respectively. These results reveal that MTIL technique is very useful to further improve the quality of AlGaN-based films, and to fabricate the high-efficiency ultraviolet light emitting diode (UV-LED).

A technique to grow low-dislocation-density AlGaN films is presented in this paper. The Al 0.17 Ga 0.83 N films using middle temperature (MT)-intermediate layer technique grown by metalorganic chemical vapor deposition on c-plane patterned sapphire were confirmed. The AlGaN films have been investigated by means of X-ray diffraction, scanning electron microscopy and transmission electron microscopy techniques. MT-intermediate layer technique can effectively reduce the dislocation density in the AlGaN films.

With the advantages of low cost, simplicity, and scalability, a direct reaction using gallium (Ga) and ammonia (NH3) has been employed to deposit GaN film on a (0001) sapphire substrate. We find that only GaN crystallites with diameters in the range of 0.4–5 µm are sparsely deposited on a bare (0001) sapphire substrate. To increase the density of the GaN nucleation site and thus form continuous GaN film, a 50-nm-thick AlN layer [grown on the (0001) sapphire substrate by metalorganic chemical vapor deposition (MOCVD) at 1150 °C in a pulsed manner] is used as a template layer. Plan-view scanning electron microscopy (SEM) and cross-sectional SEM experimental results show that the GaN film has a specular smooth surface and that the film thickness is about 10 µm after 1 h deposition. X-ray diffraction (XRD) and cathodoluminescence (CL) experimental results indicate that the formed GaN film is of single crystals with a hexagonal structure. The full widths at half-maximum (FWHM) of the (002) and (102) X-ray rocking curves are 420 and 556 arcsec, respectively. Our experimental results demonstrate that the growth of high-quality and thick GaN film via a direct reaction is possible.

We investigated the structural and optical properties of AlInGaN/AlGaN quantum wells (QWs) and the quaternary AlInGaN epilayers as a function of V/III flux ratio (flow rate of NH3). From the photoluminescence and cathodoluminescence (CL) measurements, the emission wavelengths of the AlInGaN/AlGaN QWs linearly became blueshifted and the intensities decreased with increasing the flow rate of NH3. In the X-ray rocking curve, a pattern of the sample grown at lower NH3 flow rate gives an indication of the good crystalline quality of the films. The monochromated scanning CL image of the AlInGaN epilayers measured at around 80 K showed that more densely and uniformly distributed bright spot densities, indicating In segregation regions, increased at lower NH3 flow rate. Therefore, these results suggest that the relatively decrease of NH3 flow rate results in the increase of In composition fluctuations into the AlInGaN alloys, which generate exciton localized states, and thereby enhances the emission. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Bulk growth by direct synthesis method was carried out. Thick GaN films with smooth surfaces were obtained on metalorganic chemical vapor deposition (MOCVD) GaN films. Surface became worse when bare sapphire was used as a substrate. A buffer layer was introduced and a GaN film with the thickness of about 70 μ m was obtained on sapphire in 1-hour growth. The crystallinity of the grown layer on sapphire with buffer is comparable to that on a MOCVD film.

p-GaN were grown on a nano-patterned n-GaN fabricated by nanoimprint lithography (NIL). Originality of this paper is to grow the p-GaN layer on a nano-patterned GaN. The regrowth mechanism of p-GaN on nano-processing n-GaN was identified. The carrier concentrations by capacitance-voltage characteristics of GaN p-n junction are measured, and the high in 1018 cm-3 is measured in the nano-processed sample, while it is in the middle of 1017 cm-3 in the un-processed one. The reason comes from the dangling bonds on the tilted planes from the c-axis. Therefore, a GaN p-n nano-structured sample is not a good idea, but the n-n or p-p nano-structure is a very promising, because it can improve the crystal quality by the nano-processing (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

For the first time, this paper reports a novel kind of three-flow reactor which can be developed for metal-organic chemical vapor deposition (MOCVD) system to grow GaN-based structures. Two parallel carrier gas-flow for Group-III sources and NH3 separated by a quartz plate which are also parallel to the substrate are used. The N2, which is used as a sub-flow, flows through a quartz filter perpendicular to the substrate where it meets the two parallel group III and group V source flows. This new flow arrangement enhances the mixture of group III–V sources at the contacting substrate, compared with the previous three parallel laminar gas MOCVD systems due to the perpendicular direction of the N2 sub-flow. Based on this MOCVD system with this special configuration, a mirror-like epitaxial GaN layer on sapphire substrate is obtained with an excellent uniformity. Also, the quality of the GaN layers are characterized by room temperature photoluminescence (PL) and X-ray diffraction (XRD) measurements, where the full-width at half-maximum (FWHM) of 41.12 meV for PL spectra and FWHM of about 220 arcsec for XRD rocking curve were measured, respectively. In addition, the carrier concentration and Hall mobility are found to be 2.6×1017/cm3 and 300 cm2/V s, respectively.

In the present article we report on the selective fabrication of InGaN nanostructures on Si coated GaN/sapphire substrates using the focused ion beam (FIB)/metalorganic chemical vapor deposition (MOCVD) process. InGaN quantum dots and InGaN quantum wires have been fabricated. The process combines window openings in the Si mask layer with localized highly energetic Ga+ FIB irradiation, subsequent photo-assisted wet chemical etching in a solution of KOH:H2O2 (3:1 by mole) and finally the growth of InGaN/GaN nanostructures using MOCVD. This technique proved to be efficient in realizing practically damage-free etching, hence preventing the deterioration of the nanostructure’s crystal quality. The density, size, and positions of the nanostructures could be well designed and controlled using the above process. Structural characterization by transmission electron microscopy, atomic force microscopy observations, and optical investigation by cathodoluminescence were carried out.

AlGaN growth using epitaxial lateral overgrowth (ELO) by metalorganic chemical vapor deposition on striped Ti, evaporated GaN on sapphire, has been investigated. AlGaN/AlN films growth on GaN/AlGaN superlattices (SLs) structure on the Ti masks, with various SLs growth temperature (1030, 1060 and 1090 °C) were grown. With increasing the growth temperature, AlGaN surface became flat. The AlGaN film had a cathodoluminescence peak around 345 nm. However, in secondary ion mass spectrometry (SIMS) measurement, Ti signal was detected on the top of AlGaN surface when GaN/AlGaN SLs was grown on Ti striped masks. By inserting the AlN blocking layer on SLs, Ti diffusion was stopped at the AlN layer, and the AlGaN crystalline quality was improved.

This paper reports for the first time the successful growth of a single GaN layer on an amorphous glass substrate using metal organic chemical vapor deposition (MOCVD) technique. The layers were characterized by room temperature photoluminescence and X-ray diffraction measurements. In addition, the lateral overgrowth of GaN on this substrate was also tried, which could provide an effective method to obtain high-quality GaN substrates in the near future. In comparison to the overgrowth on sapphire substrate, the lateral overgrowth on our substrate is independent of the mask stripe direction, which could indicate a different growth mechanism.

BP with the size of 50 µm to 3 mm was synthesized by the Cu flux method. The BP crystals have a zincblend structure, and the lattice constant and the cathodoluminescence peak wavelength were 4.557 A and 370 nm, respectively. GaN and AlN were grown by metalorganic chemical vapor deposition on BP. It was found that AlN grown at 1150 °C on (100)BP was grown smoothly but that grown on (111)BP had a rough surface. GaN, however, was irregularly grown on both (100) and (111)BP. It was demonstrated that AlN on (100)BP is another candidate as a substrate for a UV-light-emitting diode.

The inversion domain (ID) formed in the Al 0.17 Ga 0.83 N layer grown by metalorganic chemical vapor deposition on c-plane patterned sapphire was confirmed by transmission electron microscopy. The IDs were found to be generated at the sapphire/AlGaN interface. Most of IDs vanish in the grown layer but some IDs propagate to the surface. Contriving the growth process remarkably reduced the density of IDs.

AlxGa1-xN (x ≤0.1) epilayers grown on (0001) sapphire substrates by low-pressure metalorganic chemical vapor deposition with low-temperature (LT)-GaNP buffer have been characterized using X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is found that the full width at half maximum (FWHM) values of the GaNP-buffer-based AlxGa1-xN (x ≤0.1) epilayers decrease are lower than that of the conventional GaN-buffer-based AlxGa1-xN (x ≤0.1) epilayers, but the difference becomes smaller as the Al composition increases. These results could be mainly attributed to a longer diffusion length with the GaNP buffer layer than with the GaN buffer layer.

The growth of bulk GaN by sublimation method and a homoepitaxial growth by MOCVD are reported. A photo-pumped stimulated emission is obtained from a homoepitaxial layer. The source powder used as a source in the sublimation method is investigated in detail, and it is shown that the powder contains many kinds of compounds consisting mainly of gallium, nitrogen and hydrogen. Growth nucleation control is performed by partly covering an MOCVD-GaN or a scratched-sapphire (0001) by Si02. Hexagonal columns of the size of about 200 μm in diameter and about 200 μm in height are selectively and uniformly grown at the window sites. This technique enables the device processing of crystallites and also helps to increase crystal size by increasing growth time, since it prevents the nucleation of new crystallites which work as sink of the growing species.

The effect of oxygen mixed in nitrogen on p-type activation in Mg-doped GaN epilayers grown by metalorganic chemical vapor deposition (MOCVD) was investigated. The samples annealed in N2/O2 (1%) ambient exhibited the best electrical properties with respect to hole concentration. SIMS data suggested that oxygen reacted with hydrogen present in the Mg-doped GaN samples during the thermal annealing process, thereby enhancing the activation of Mg acceptors.

Plan-view transmission electron microscopy (TEM) and cathodoluminescence (CL) images were taken for the same sample at exactly the same location in n-type GaN grown on sapphire substrate by metalorganic chemical vapor deposition (MOCVD). There was a clear one to one correspondence between the dark spots observed in CL images and the dislocations in TEM foils, indicating that the dislocations are non-radiative recombination centers. The hole diffusion length in n-type GaN was estimated to be neighboring 50 nm by comparing the diameters of the dark spots in thick samples used for CL and samples that were thinned for TEM observation. The efficiency of light emission is high as long as the minority carrier diffusion length is shorter than the dislocation spacing.

Homoepitaxial growth of GaN on bulk GaN prepared by the sublimation method was performed by metalorganic chemical vapor deposition (MOCVD). Two kinds of bulk substrates were used for homoepitaxial growth: (i) a polished bulk GaN C-face, selectively grown on MOCVD-GaN on a sapphire (0001) substrate which was partly covered by SiO2 (“quasi-bulk” GaN) and (ii) a bulk GaN spontaneously nucleated on the source powder used in the sublimation method (“free-standing” bulk GaN). A smooth surface and strong CL band-edge emission from the homoepitaxial layer were obtained when proper surface pretreatment of the substrate, such as H3PO4 etching, RIE and photoassisted wet chemical etching (PAW), was adapted before loading into the MOCVD reactor. The CL intensity of the band-edge emission was stronger and the CL image more uniform for homoepitaxial GaN compared to that of heteroepitaxial GaN on sapphire. The dislocation density of the homoepitaxial layer was also decreased after proper surface treatment of the substrate.

Nucleation of GaN crystallites by sublimation method on sapphire (0001), scratched sapphire (0001), SiO2, Si (111), and metalorganic chemical vapor deposition(MOCVD)-GaN/sapphire (0001) was investigated. The density of the nuclei on SiO2 and Si (111) was estimated to be 6 × 103/cm2. On the other hand, a continuous film rather than discrete crystallites was obtained on both the MOCVD-GaN and the scratched sapphire. Growth nucleation control was performed by partly covering the MOCVD-GaN or scratched sapphire (0001) with SiO2. As a result, hexagonal columns about 200 µm in diameter and 200 µm high were selectively and uniformly grown at the window sites. The diameter of each hexagonal column was much larger than the width of each window. This method can be used for device processing utilizing the crystallites.

A GaN film with nominal thickness of 0.6 µ m was homoepitaxially deposited on a sublimation-grown GaN single-crystal substrate. An electron-transparent area of 10 µ m×10 µ m prepared by focused Ga ion beam machining was examined by transmission electron microscopy. In addition to the dislocations on the basal plane of the wurtzite unit cell, another type of dislocation, near pure edge in character and aligned close to the c-axis direction, was found in the GaN substrate crystal. Neither type of dislocation threaded to the top surface. Dislocation-free growth was achieved in the GaN homoepitaxial film.