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(0 0 0 1) oriented GaN epilayer grown on [formula omitted] sapphire by MOCVD
Ist Teil von
Journal of crystal growth, 2001-09, Vol.231 (1), p.41-47
Ort / Verlag
Amsterdam: Elsevier B.V
Erscheinungsjahr
2001
Quelle
Elsevier Journal Backfiles on ScienceDirect (DFG Nationallizenzen)
Beschreibungen/Notizen
Since the major advantage of
(1
1
2
̄
0)
sapphire substrate is the ability to easily form cleaved facets, which is important for the fabrication of edge-emitting lasers, it is meaningful to investigate the GaN epilayer grown on
(1
1
2
̄
0)
sapphire substrate. X-ray diffraction (XRD) measurement indicates that the GaN growth is still along (0
0
0
1) direction even on
(1
1
2
̄
0)
sapphire substrate. However, compared with the GaN grown on (0
0
0
1) sapphire substrate, the GaN layer on
(1
1
2
̄
0)
sapphire substrate shows a larger
c-axis lattice constant and smaller
a-axis lattice constant, which indicates that there exists an enhanced lattice-mismatch compared with the case on (0
0
0
1) sapphire substrate. The detailed XRD measurement indicates that the strain exerted on the GaN on
(1
1
2
̄
0)
sapphire substrate is increased by 0.03% compared with that on (0
0
0
1) sapphire substrate. Furthermore, the low-temperature photoluminescence indicates that the GaN on
(1
1
2
̄
0)
sapphire substrate shows a 4.5
meV blue-shift compared with the GaN on (0
0
0
1) sapphire substrate, which is in a good agreement with our calculation based on the lattice-mismatch induced strain model. A crystallographic depict is proposed for a good explanation of a GaN layer growth on
(1
1
2
̄
0)
sapphire substrate. By selective-area diffraction (SAD) and high-resolution transmission electron microscopy measurement (HREM), the in-plane orientation relationship is determined to be
(1
1
2
̄
0)
GaN
∥(1
1
̄
0
0)
sapphire
and
(1
1
̄
0
0)
GaN
∥(0
0
0
1)
sapphire
, which also shows that a larger lattice-mismatch between (0
0
0
1) GaN and
(1
1
2
̄
0)
sapphire substrate occurs and thus gives rise to an enhanced compressive strain. In turn, it supports our above discussion.