GaN Microcrystals Research Articles

Observation of Dark Spots and Dark Lines of GaN Microcrystals Grown by Nitridation of Gallium Sulfide

High-spatial-resolution (50 nm) cathodoluminescence images in the ultra-violet region (365 nm) and in the yellow region (570 nm) were taken at room temperature for GaN bulk crystals under a scanning electron microscope equipped with a monochromator and a real-time RGB-separation detector. The crystals were grown by nitridation of Ga 2 S 3 and had a c-facet and side facets with Miller indices of [110x] or [112y]. Dark spots were observed only on the side facets while dark lines only on a c-facet. Dark lines stretch in the direction of (1100) or (11200) and end as a dark spot on side facets. Dark spot density was 10 9 cm -2 . The nonuniformity of yellow luminescence and its irrelevance to the existence of dark lines suggest an extrinsic defect for the origin of yellow luminescence, such as carbon impurity.

Observation of Dark Spots and Dark Lines of GaN Microcrystals Grown by Nitridation of Gallium Sulfide

High-spatial-resolution (50 nm) cathodoluminescence images in the ultra-violet region (365 nm) and in the yellow region (570 nm) were taken at room temperature for GaN bulk crystals under a scanning electron microscope equipped with a monochromator and a real-time RGB-separation detector. The crystals were grown by nitridation of Ga2S3 and had a c-facet and side facets with Miller indices of 10x or 11y. Dark spots were observed only on the side facets while dark lines only on a c-facet. Dark lines stretch in the direction of 〈100〉 or 〈1100〉 and end as a dark spot on side facets. Dark spot density was 109 cm—2. The nonuniformity of yellow luminescence and its irrelevance to the existence of dark lines suggest an extrinsic defect for the origin of yellow luminescence, such as carbon impurity.

Catalytic growth of high quality GaN micro-crystals

GaN micro-crystals were catalytically grown using Ni-mesh in direct reaction of gallium and ammonia. At 1100°C, the growth rate of the GaN crystals in the presence of Ni catalyst was almost ten times higher than in the absence of the catalyst. The use of the catalyst induced the increase of GaN crystal size. The structural characterization of the GaN crystal showed the growth of dislocation free hexagonal GaN single crystal. PL spectrum showed a strong band edge emission at the energy position of ∼3.35 eV with FWHM of ∼115 meV. The time-resolved photoluminescence measurements also revealed the growth of high quality GaN micro-crystal grains. The catalytic activity for the growth of the GaN crystals was discussed based on the in situ analyzed gas composition during the growth.

Characterization of Mg-Doped GaN Micro-Crystals Grown by Direct Reaction of Gallium and Ammonia

Mg-doped GaN micro-crystals were prepared by the direct reaction of metal gallium and ammonia using magnesium chloride (MgCl2) as Mg doping source. The growth of microcrystalline hexagonal GaN was clearly found from scanning electron microscopy and TEM measurements. The grain size of Mg-doped GaN crystals was larger than that of undoped GaN. Room temperature PL and CL spectra for Mg-doped GaN micro-crystal showed the blue emission at 2.75 and 2.85 eV, respectively.

STM excited electroluminescence of GaN microcrystals

We report on a system of GaN crystallites grown onto Si substrates with and without preconditioning of the surface layer by Si implantation. Upon electronic excitation by the tip of a scanning tunneling microscope (STM), site-dependent luminescence spectra are obtained, implying the possibility to correlate structural and optical properties at the nanometer scale. Voltage-polarity-dependent measurements lead to a simple model for the excitation mechanism.