Improved surface morphology in GaN homoepitaxy by NH3-source molecular-beam epitaxy

Abstract

Effects of hydrogen on the morphology and electrical properties of GaN grown by plasma-assisted molecularbeam epitaxy Appl. Phys. Lett. 86, 121914 (2005); 10.1063/1.1890482 Effect of template morphology on the efficiency of InGaN ∕ GaN quantum wells and light-emitting diodes grown by molecular-beam epitaxy Appl. Phys. Lett. 86, 121110 (2005); 10.1063/1.1884745Effect of N to Ga flux ratio on the GaN surface morphologies grown at high temperature by plasma-assisted molecular-beam epitaxy GaN homoepitaxial layers of improved surface morphology were obtained by a NH 3 -source molecular-beam epitaxy method supplying a proper reactive NH 3 -to-Ga flux ratio ͑V/III ratio͒ on the growing surface, combined with a procedure to prevent the surface roughening of the GaN/ ͑0001͒ Al 2 O 3 epitaxial templates, which were prepared by metalorganic vapor-phase epitaxy. In situ monitoring on the heated templates revealed their thermal decomposition above 700°C in ultrahigh vacuum, which gave rise to surface unevenness of both initially atomically flat templates and the homoepitaxial layers. The surface flatness was maintained by depositing the ''flux-modulated'' GaN prior to the high-temperature growth, where Ga flux was supplied intermittently during heating the template under continuous NH 3 flow. The increase in V/III ratio greatly improved the surface flatness. As a result of the epilayer/template interface control and growth optimization, the epilayers exhibited higher mobility, smaller full width at half-maximum value ͑34 meV͒ of excitonic photoluminescence ͑PL͒ peak, and longer PL lifetime of 180 ps at 293 K.

Growth regimes during homoepitaxial growth of GaN by ammonia molecular beam epitaxy

“…Koida et al reported that decomposition of the GaN template during heating prior to growth resulted in degraded surface morphology of subsequent ammonia MBE GaN. 19 We believe that this was not a contributing factor here for three reasons: first, because the GaN template was prevented from decomposition during heating by starting the ammonia flow at a low temperature, and the RHEED was monitored to confirm a smooth starting surface; second, because a smooth starting surface of the GaN template can be seen in Fig. 7, indicating that pits were not formed prior to initiation of ammonia MBE GaN growth; and finally, because the same surface features were observed for GaN buffer layers grown on SiC substrates with AlN nucleation layers as on MOCVD templates.…”