12.2 Heteroepitaxy
361
Fig. 12.14 SEM
cross-sectional image of
GaN grown on a structured
Si(111) substrate. The
laterally grown wings
extend about 2.5 µm over
the grooves. The thickness
of the GaN layer is 0.5 µm
on the bottom of the
grooves, while it is 1.4 µm
on top of the ridges.
Reprinted with permission
from [1148], ©2001 AIP
(a)
(b)
(c)
(d)
GaN
sapphire
GaN
SiN mask
Fig. 12.15 SEM images of GaN a growing through the openings of a random SiN mask, b laterally overgrowing the
mask and coalescing and c eventually forming a flat film. Bar widths are 2 µm, 1 µm and 10 µm. d Cross-section TEM
image. Adapted from [1149]
Using patterned substrates with stripe-like mesas and promoting the growth on a sidewall of the
mesa, the direction of GaN growth front can be steered into a semipolar direction (cmp. Sect. 16.4.3).
The r-plane sapphire substrate with etched mesa stripes oriented along the [11.0] direction exposes
[00.1]-oriented sidewall facets on which the GaN grows along its c-axis; The angle of 57.6
◦ between
the r- and the c-planes of sapphire is very close to the angle (3.22c) of 58.4
◦ between the GaN semipolar
(11.2) and the (00.1) plane. The flat growth front represents a (11.2) facet [1151] (Fig. 12.16). After
coalescence of grains from various mesas, a flat (11.2) surface arises, allowing the reduction of various
defects including basal stacking faults [1152, 1153].
361
Fig. 12.14 SEM
cross-sectional image of
GaN grown on a structured
Si(111) substrate. The
laterally grown wings
extend about 2.5 µm over
the grooves. The thickness
of the GaN layer is 0.5 µm
on the bottom of the
grooves, while it is 1.4 µm
on top of the ridges.
Reprinted with permission
from [1148], ©2001 AIP
(a)
(b)
(c)
(d)
GaN
sapphire
GaN
SiN mask
Fig. 12.15 SEM images of GaN a growing through the openings of a random SiN mask, b laterally overgrowing the
mask and coalescing and c eventually forming a flat film. Bar widths are 2 µm, 1 µm and 10 µm. d Cross-section TEM
image. Adapted from [1149]
Using patterned substrates with stripe-like mesas and promoting the growth on a sidewall of the
mesa, the direction of GaN growth front can be steered into a semipolar direction (cmp. Sect. 16.4.3).
The r-plane sapphire substrate with etched mesa stripes oriented along the [11.0] direction exposes
[00.1]-oriented sidewall facets on which the GaN grows along its c-axis; The angle of 57.6
◦ between
the r- and the c-planes of sapphire is very close to the angle (3.22c) of 58.4
◦ between the GaN semipolar
(11.2) and the (00.1) plane. The flat growth front represents a (11.2) facet [1151] (Fig. 12.16). After
coalescence of grains from various mesas, a flat (11.2) surface arises, allowing the reduction of various
defects including basal stacking faults [1152, 1153].