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

Abstract

Transmission 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)

Semipolar GaN grown on foreign substrates: a review

“…This was confirmed by Araki et al [50]. Consistently, several groups found a much smoother GaN surface when grown on a wafer with a miscut of about −0.5 • toward the c-plane [50][51][52]. Although we could confirm this observation, we found significantly better bulk properties of layers grown on the r-plane sapphire miscut just in the opposite direction by about the same amount, as revealed by smaller FWHMs of x-ray and PL lines [33].…”

Joint effect of miscut r-plane sapphire substrate and different nucleation layers on structural characteristics of non-polar a-plane GaN films

“…It was speculated that the insufficient migration of Ga adatoms in the LT-GaN NL on the MRSS with a miscut angle larger than 1.0°could generate excessive narrow steps that would finally cause a disordered lattice and additional misfit dislocations in the as-grown a-plane GaN film. 24 On the other hand, as shown in Fig. 6(b), the XRC FWHM values measured along both the [0001] and [11 ¯00] directions for the five series II samples S A1 -S A5 grown over the HT-AlN NLs are much smaller than those for the five series I samples S G1 -S G5 grown over the LT-GaN NLs.…”