AlN films were grown on AlN/sapphire templates at 1400–1500 °C using low‐pressure hydride vapor phase epitaxy (LP‐HVPE). Compared to the step‐flow growth of AlN film at 1200 °C with growth rate of 2.1 μm/h, AlN films with atomic steps were obtained at 1400–1500 °C even with high growth rate. For the AlN film grown at 1450 °C with growth rate of 14.3 μm/h, the RMS value is 0.75 nm and the FWHM values of (0002) and (10‐12) X‐ray rocking curve (XRC) are 351 and 781 arcsec, respectively. Since the FWHM value of (10‐12) XRC for the AlN/sapphire template is 1492 arcsec, the crystal quality of HVPE‐grown AlN is greatly improved compared with the AlN/sapphire template, which is also confirmed by TEM observation. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

A novel method, using metal ethylenediamine tetraacetic acid (EDTA) complexes as starting materials, is proposed to synthesize III-nitride microcrystals. Ga (Zn, Ga)-EDTA·NH 4 and In-EDTA·NH 4 complexes were reacted with NH 3 in the temperature range of 1020-1150 o C and 300-620 o C, respectively. SEM observation and X-ray diffraction patterns show that pure phase hexagonal GaN and InN are obtained. The CL peak intensity of GaN increases as the synthesis temperature increases up to 1100 o C. The dependence of CL peak intensity on Zn doping content indicates good doping control. For InN synthesis, the temperature window is very narrow and the reaction evolves from In 2 O 3 to InN.1 Introduction III-nitride microcrystals are promising materials for field emission display (FED), vacuum fluorescent display (VFD) and many other applications due to the advantages covering high reliability, low electricity consumption and controllable emission wavelength by doping with various elements. For GaN microcrystal, the conventional synthesis methods include nitridation of Ga metal by NH 3 [1], but the reaction efficiency is low. Another method is nitridation of Ga 2 S 3 in NH 3 [2], however, a by-product in this method, H 2 S, is not favourable. A two-stage method was also proposed [3], where the first step is a direct reaction of Ga with NH 3 to form seed GaN crystal, and a reaction of Ga with HCl to form GaCl, respectively. The second step is a reaction of GaCl with NH 3 on seed GaN. Although this method can enhance the reaction speed using vapour phase synthesis, the equipment and the procedures are complicated. For InN microcrystal synthesis, various starting materials were reported. For instances, direct reaction of In metal with NH 3 [4], reaction of In 2 S 3 and NaNH 2 [5], which produces H 2 S, and reaction of InCl 3 and Li 3 N [6], which yields mixed phases. The above methods for fabricating III-nitride microcrystals suffer from low reaction efficiency or complicated processes, and difficulty in doping control. Therefore, it is necessary to search for high efficient and environmentally friendly method of synthesis with easily control of metal compositions. Since ethylenediamine tetraacetic acid (EDTA: C 10 H 16 N 2 O 8 ) forms stable and water-soluble metal complexes, homogeneous mixture of several metal-EDTA complexes can be obtained from solution and be transferred into solid powder using a spray-dry technique, which was reported to fabricate Ba, Sr, Ti, Y and Cu-EDTA complexes and to further synthesize metal oxide powders such as (Ba, Sr) TiO 3 and YBa 2 Cu 3 O 7 with them [7,8].In this work, we propose a method adopting metal-EDTA complexes as starting materials to fabricate III-nitride microcrystals. Ga (Ga, Zn)-EDTA·NH 4 and In-EDTA·NH 4 are reacted with NH 3 , respectively. The pure phase hexagonal GaN, Zn-doped GaN, and InN microcrystals are obtained, respectively.

InGaN/GaN stripe structures and hexagonal pyramid structures were grown on sapphire (0001) by lowpressure metalorganic vapor phase epitaxy (LP-MOVPE). It was observed that the indium composition at (0001) was greater than that at {11 2 2}. For InGaN/GaN stripe and pyramid structures with {10 1 1}, the thickness, CL peak wavelength and CL intensity gradually increased from the bottom to the top of the facet. It is considered that this behavior on the facet is due to the indium diffusion mechanism or indium composition pulling effect.