GaN substrates are desirable for fabricating ultra-violet LEDs and LDs, and high-power and high-frequency transistors.
High-quality GaN single crystals can be obtained by using Na flux method, but the growth habit of bulk crystals must be
controlled. In this study, we investigated the effects of additives (Ca, Ba) on the growth habit and impurity concentration
in the crystals. The aspect ratio (c/a) of the crystals was increased by increasing the amount of additives, showing that the
growth habit could be changed from the pyramidal shape to the prism shape. Ba concentration was below the detection
limit (1x1015 atoms/cm3).
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