Na-flux Method Research Articles

Conditions for seeded growth of GaN crystals by the Na flux method

Conditions for seeded growth of GaN crystals by the Na flux method were investigated. Seeded growth in the Na flux could be achieved under temperature–N 2 pressure conditions between the condition of GaN formation without seeding and the condition of GaN decomposition. GaN single crystals with a maximum area of 3.0×1.5 mm 2 and thickness of 1.0 mm were grown from seeds at 850 °C and 2 MPa of N 2 for 200 h. The crystal growth occurred selectively on the (0001) Ga-polar surface of the platelet seed crystals. The growth rate in the c direction was higher than those of other directions and increased with growth temperature and N 2 pressure. The maximum growth rate in the c direction was about 4 μm/h at 850 °C and 2 MPa of N 2.

Influence of pressure control on the growth of bulk GaN single crystal using a Na flux

We investigated the influence of N 2 pressure control on the growth of bulk GaN crystals by using a Na flux. GaN single crystals with a maximum dimension of 3 mm could be obtained by this method, though smaller crystals of 0.5–2 mm in size have been grown without pressure control. This suggested significant effects of additional NH 3 gas on growth of GaN crystals in the Na flux method.

Morphology and Polarity of GaN Single Crystals Synthesized by the Na Flux Method

The correlation between morphology and polarity was investigated for GaN single crystals synthesized by the Na flux method. The polarity was identified by using anomalous X-ray dispersion. Colorless transparent prismatic single crystals were classified into three types. The first had a smooth basal plane face and no hexagonal pyramidal faces, the second had smooth pyramidal faces, and the third had a rough basal plane face and rough pyramidal faces. The prismatic crystals with smooth surfaces had N-polarity and grew in the −c direction, whereas the crystals having rough surfaces had Ga-polarity and grew in the +c direction. In colorless transparent platelet single crystals, one side of the basal planes had a mirror smooth surface, while the other side had many step edges and hexagonal pits. The smooth basal plane and the rough basal plane were the (0001̄) N-face and (0001) Ga-face, respectively. Black pyramidal crystals had a smooth (0001) basal plane face corresponding to the Ga-face.

Growth of AlxGa1xN and InyGa1yN Single Crystals Using the Na Flux Method

The bulk crystal growth of Al x Ga 1-x N and In y Ga 1-y N was investigated by the Na flux method using NaN 3 , Ga, and Al or In. The crystal size and the yield of the crystal growth were different between Al x Ga 1-x N and In y Ga 1-y N. According to Vegard's law, the largest Al composition x in Al x Ga 1-x N and the largest In composition y in In y Ga 1-y N were 0.22 and 0.7, respectively.

Growth of AlxGa1-xN and InyGa1-yN Single Crystals Using the Na Flux Method

The bulk crystal growth of Al x Ga 1-x N and In y Ga 1-y N was investigated by the Na flux method using NaN 3 , Ga, and Al or In. The crystal size and the yield of the crystal growth were different between Al x Ga 1-x N and In y Ga 1-y N. According to Vegard's law, the largest Al composition x in Al x Ga 1-x N and the largest In composition y in In y Ga 1-y N were 0.22 and 0.7, respectively.

Growth Conditions and Morphology of GaN Single Crystals Fabricated by the Na Flux Method.

GaN single crystals were synthesized by using the Na-Ga melt at 700-850°C and 1-5 MPa of N2 for 200h. The formation of GaN was not observed at 800°C under 1 MPa of N2, and at 850°C and 1.5MPa of N2. GaN single crystals were obtained lower temperatures and/or the higher N2 pressures. The morphology of the crystals tended to change from prismatic to platelet by decreasing the growth temperature and/or increasing N2 pressure. Colorless transparent prismatic single crystals with a size of about 1.0±0.5±0.5mm3 were obtained by adopting a three-step heating process in which the temperature was increased from 750°C at 0.5°C/h to 800°C under 3MPa of N2.

Growth of nitride crystals, BN, AlN and GaN by using a Na flux

Bulk crystals of BN, AlN and GaN were grown by means of Na flux. All these crystals were grown at a temperature of 800°C and a nitrogen pressure of 100 atm, relatively lower than that required by many flux and melt growth methods. High-quality GaN single crystals as large as 0.5 mm were obtained. Furthermore, the oriented GaN crystals were obtained by means of the seeded Na flux method with the addition of oriented AlN (0001) film in the growth ambient. The nucleation of bulk GaN was spatially confined on top of the AlN film and grown with the GaN [0001] axis parallel to the AlN [0001] axis. In addition, the h-BN polycrystals were confirmed by the h-BN (0002) peak of X-ray diffraction (XRD) at 2θ=26.700. A hexagonal grain with a size as large as 2 μm was observed by scanning electron microscopy (SEM). Likewise, AlN crystals were also obtained from Al wires.