We report on the polarity control of GaN
regrown on pulsed-laser-deposition-grown N-polar AlN on a
metalorganic-vapor-phase-epitaxy-grown Ga-polar GaN template. The polarity of
the regrown GaN, which was confirmed using aqueous KOH solutions, can be
inverted from that of AlN by inserting a low-temperature GaN (LT-GaN) buffer
layer. We hypothetically ascribe the Ga-polarity selection of GaN on the LT-GaN
buffer layer to the mixed polarity of LT-GaN grains and higher growth rate of
the Ga-polar grain, which covers up the N-polar grain during the initial stage
of the high-temperature growth. The X-ray rocking curve analysis revealed that
the edge-dislocation density in the N-polar regrown GaN is 5 to 8 times smaller
than that in the Ga-polar regrown GaN. N-polar GaN grows directly on N-polar
AlN at higher temperatures. Therefore, nucleus islands grow larger than those
of LT-GaN and the area fraction of coalescence boundaries between islands,
where edge dislocations emerge, becomes smaller.
Source:IOPscience
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