In situ characterization of GaN quantum dot growth with reflection high-energy electron diffraction and line-of-sight mass spectrometry
We have investigated the Ga-adlayer mediated growth of GaN quantum dots at 707 degrees C on AlN (0001) by simultaneous use of in situ reflection high-energy electron diffraction and line-of-sight quadrupole mass spectrometry during rf-plasma assisted molecular beam epitaxy (PA-MBE). We have found that the Ga-adsorbate coverage of 1.0 ML (monolayer) is critical in the mediation of a fundamental change in the GaN Stranski-Krastanov (SK) growth mode on AlN. When the Ga-adsorbate coverage was less than 1.0 ML, the SK transition occurred during GaN growth. For larger Ga-adsorbate coverages, the SK transition occurred after the desorption of the Ga coverage in excess of 1.0 ML. We performed variable GaN coverage growth experiments followed by desorption of the Ga adsorbate and subsequent GaN thermal decomposition to determine that the critical GaN coverage for the SK transition was less than 2.0 ML under Ga-droplet PA-MBE growth conditions.