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Results of gallium nitride crystallization by ammonothermal method are presented. GaN crystals grown earlier by a HVPE method on an ammonothermal GaN substrate and an MOCVD-GaN/sapphire template were used as seeds. Structural and optical properties of the obtained materials are studied and compared. Large radius of curvature (>100 m) and low dislocation density (7×10 4 cm −2 ) can be reproduced in the ammonothermal method using an HVPE-GaN seed grown before on ammonothermal GaN. This proves that the use of HVPE-GaN grown on ammonothermal seeds allows to reproduce high crystallinity in a subsequent ammonothermal growth. It also demonstrates that a much more effective multiplication process of high quality GaN can be launched using a combination of the ammonothermal and HVPE methods. [ABSTRACT FROM AUTHOR]

• Round shape of seeds allowed to crystallize GaN without cracks at the edges. • 60 µm/day growth rate in ammonothermal crystallization is presented. • Etch pit density in laterally-grown GaN was of the order of 102 cm−2. • Stress Induced Polarization Effect (SIPE) was visible in Am-GaN crystals. Progress in basic ammonothermal gallium nitride crystallization is reported. In order to prevent the appearance of cracks in growing GaN a new shape of native seeds is proposed. Crystallization results on irregular (old) and round (new) shapes are compared in terms of growth rate and structural quality. The new type of seeds allowed to grow crystals twice as fast without losing the very high structural quality. Etch pit density in the new-grown material is examined and compared to that in the seeds. Material deposited in vertical <000–1> and lateral <11–20> directions is analyzed. In the latter case the etch pit density is as low as 102 cm−2. An influence of growth process parameters and crystal growth configuration on the structural quality of crystallized GaN is discussed. [ABSTRACT FROM AUTHOR]

Study on the sources of stress in HVPE-GaN layer crystallized on 1-in. ammonothermally grown GaN seed is presented in this paper. Characterization by means of X-ray diffraction and transmission electron microscopy is performed. HVPE-GaN samples of high quality and those with visible quality deterioration are investigated on c-plane and m-plane cross-sections. Special attention is paid to HVPE material growing in semi-polar and non-polar directions on the edges of the seed and the growing layer. It is shown that this material generates significant stress leading to a structural deterioration of HVPE-GaN growing in the c -direction. [ABSTRACT FROM AUTHOR]

GaN/AlGaN quantum wells (QWs) were grown by metal–organic vapor phase epitaxy (MOVPE) on c -, a -, m -, and (20.1)-plane GaN substrates obtained by the ammonothermal method in the same MOVPE process, i.e. a process with growth parameters optimized for c -plane GaN templates. The structural properties of GaN/AlGaN QWs were carefully investigated by high angle annular dark field scanning transmission electron microscopy. Sharp GaN/AlGaN interfaces were seen for QWs grown on the c -, a -, and m -plane GaN substrates, but very rough interfaces with {1-100} and {1-101} facets were observed on the (20.1)-plane GaN substrate. In addition, the Al-rich region of AlGaN and GaN transition was identified for each of the GaN/AlGaN QW samples deposited in this process. The thickness and composition of this region varied with the crystallographic orientation of GaN substrates. [ABSTRACT FROM AUTHOR]

One of the main advantages of the hydride vapor phase epitaxy (HVPE) method for crystallizing bulk gallium nitride is the crystallization of GaN with a relatively high growth rate (>100 μm/h). In this paper various growth rates in the c -direction during crystallization of GaN by HVPE on ammonothermally grown GaN crystals are determined and examined. The influence of the highest (380 μm/h) and the lowest (40 μm/h) growth rate on the structural quality and purity of the HVPE-GaN crystals is analyzed. The optimal macroscopically stable growth rate (without cracks and pits) and the way of achieving it are presented and discussed. [ABSTRACT FROM AUTHOR]

The results of the Hydride Vapor Phase Epitaxy (HVPE) on ammonothermal GaN seeds (Am-GaN) with various misorientations: 0.3, 0.5 and 1 degree to the [1 0 −1 0] and [1 1 −2 0] directions are presented. Growth rate and structural quality of the HVPE-GaN layers are analyzed. Morphology of the crystal growing surface at the beginning of the crystallization process (after one and two hours of growth) and at the end of it (after eight hours) is presented as a function of the Am-GaN seed misorientation. Based on these results a rough growth model is proposed and discussed in detail. [ABSTRACT FROM AUTHOR]

Abstract: GaN epilayers were grown by metalorganic chemical vapor deposition (MOCVD) on c-, m-, a-, and (20.1)-plane GaN substrates obtained by the ammonothermal method. The influence of (i) the surface preparation of substrates, (ii) MOCVD growth parameters, and (iii) the crystallographic orientation of substrates on the structural and optical properties of GaN epilayers was investigated and carefully analyzed. It was observed that the polishing of substrates and their misorientation have strong impact on the quality of GaN epilayers grown on these substrates. The MOCVD growth process was optimized for epilayers grown on m-plane GaN substrates. The best structural and optical properties were achieved for epilayers deposited at 1075°C and the total reactor pressure of 50mbar. These conditions were applied to grow GaN epilayers on substrates with other (c-, a-, and (20.1)-plane) crystallographic orientations in the same MOCVD process. Particularly good optical properties were obtained for GaN epilayers deposited on polar and non-polar (m- and a-plane) substrates, whereas slightly worse optical properties were observed for epilayers deposited on the semi-polar substrate. It therefore means that MOCVD growth conditions optimized for a given crystallographic direction (m-plane direction in this case) work rather well also for other crystallographic directions. [Copyright &y& Elsevier]

Abstract: In this paper we present progress made recently in the development of the growth of truly bulk GaN crystals by the ammonothermal method in basic environment. High quality 2-in c-plane GaN seeds are shown. Non-polar wafers can also be cut out from thick GaN crystals grown by ammonothermal method. Perfect crystallinity manifests in very narrow peaks in X-ray rocking curves (the full width at half maximum equals about 15arcsec). GaN epilayers deposited on these substrates exhibit intrinsic narrow exciton lines, which are very sensitive to the optical selection rules typical for hexagonal symmetry, proving the truly non-polar character of such AMMONO-GaN substrates. Other challenges like homogenous insulating properties or high p-type conductivity have been also accomplished by means of ammonothermal method. Semi-insulating crystals of resistivity up to 1011 Ωcm and p-type conductivity within hole concentration up to 1018 cm−3 are already available in diameters up to 1.5-in. [ABSTRACT FROM AUTHOR]