Off‐angle dependence of void formation and defect behavior in a ‐plane MOVPE‐GaN on r ‐plane sapphire substrate

Abstract

AbstractTransmission electron microscope (TEM) observation was performed to analyze microstructures in a (11$ \bar 2 $0)‐plane GaN thin films grown by metal‐organic vapor‐phase epitaxy (MOVPE) on a r (1$ \bar 1 $02)‐plane sapphire substrate Special attention was paid to an influence of small off‐angle of the substrate plane to morphology of defects in the thin films. From the TEM observation, the following results were drawn. (1) The crystallographic orientation relationship between GaN and sapphire substrate is (11$ \bar 2 $0)[0001][$ \bar 1 $100]GaN // (1$ \bar 1 $02)[$ \bar 1 $101][11$ \bar 2 $0]sapphire. The direction of +c ‐polarity coincides with that reported previously. (2) The pits on the surface are formed on the grain boundaries of GaN. (3) The density of pits is related with the density of nucleation of GaN‐islands on the substrate. The increase in density of pits with the off‐angle can be explained by the increase of nucleation sites provided by atomic steps on the substrate. (4) The side‐wall planes of pits and voids are considered to be closed to ±(0001), ±(11$ \bar 2 $4), and (11$ \bar 2 $2). (5) The formation of pits and voids are attributable to the trend that such inclining planes as (11$ \bar 2 $2) and (11$ \bar 2 $4) are stable compared with +c (0001). A possible technique for reduction of defects is also discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)