This study investigates the crystallographic polarity transition of AIN layers grown by high temperature metalorganic chemical vapor deposition (HT-MOCVD), with varying trimethylaluminum (TMAI) pre-flow rates. AIN layers grown without TMAI pre-flow had a mixed polarity, consisting of Al- and N-polarity, and exhibited a rough surface. With an increasing rate of TMAI pre-flow, the AIN layer was changed to an Al-polarity, with a smooth surface morphology. Finally, AIN nano-pillars and nano-rods of Al-polarity were fabricated by etching a mixed polarity AIN layer using an aqueous KOH solution.

The self-compensation effect in Si-doped Al 0.55 Ga 0.45 N layers was investigated using different SiH 4 /III ratios. The degree of compressive strain changed with SiH 4 flow rate during growth. With a low SiH 4 /III ratio of 2.46 ' 10 %6 , compressive strain was increased in comparison with the un-doped case. However, above this SiH 4 /III ratio, compressive strain decreased from ε xx = %5.07 ' 10 %3 to 4.28 ' 10 %3 when the ratio was increased to 4.1 ' 10 %5 . For higher SiH 4 /III ratios, the compressive strain again increased, which is attributed to the self-compensation effect of Si atoms. A similar tendency was observed in Photo-luminescence (PL) results. While the UV-to-violet ratio (I UV /I VL ) of room-temperature PL remained to be almost constant for SiH 4 /III ratios below 8.2 ' 10 %5 , I UV /I VL decreased rapidly above this value, as a result of self-compensation of Si atoms. These results were in good agreement with the Hall effect measurements.

In this study, we suggest a polarity-selective in-situ thermal etching and re-growth process for the fabrication of high quality Al terminated AIN epilayers by high temperature metalorganic chemical vapor deposition. Mixed-polar AIN layers grown on a thin (5 nm) buffer layer at a high temperature (950 degrees C) exhibited high crystalline quality. Surface morphologies of in-situ thermally etched AIN layers depended on the grain size and distance between grains. Increasing the initial grain size and diminishing the space between grains increased etching depth and width. During re-growth, threading dislocations were bent and annihilated in the vicinity of voids, which were formed by lateral growth of Al-polar AIN regions after thermal etching. Finally, a high quality Al-polar AIN template, as verified by an aqueous KOH solution, was successfully fabricated.