4.6 Epitaxial Technology of High Quality GaN on SiC Substrate
65
Fig. 4.19 The regular
tetrahedron unit of SiC [40]
bonds, indicating that SiC has a structure with stabilized combination energy. This
is reflected by a high atomic energy value of 1250 kJ/mol. SiC has a high Debye
temperature of 1200–1400 K. Therefore, SiC has excellent mechanical and chemical
properties such as good stability, high hardness, wear resistance, and high melting
temperature under normal pressure.
The Si atomic layer and the C atomic layer in the single crystal SiC constitute
a basic diatomic layer. Si–C diatomic layers are alternately stacked in a certain
sequence to form SiC crystals. The difference in the stacking sequence of the diatomic
layers leads to different crystal structures, i.e., the formation of polyisomers of SiC,
or homogenous polymorphisms. More than 250 crystal structural morphologies have
been discovered [41]. The most important one are 3C, 2H, 4H, 6H, 8H, 9R, 10H,
14H, 15R, 20H, 21H, 24R, etc., belonging to three basic crystallography types:
cubic (C), hexagonal (H), diamond (R). Generally, the polytypes of hexagonal and
rhomboid structures are collectively referred to as α-SiC; the SiC of cubic structure is
collectively referred to as β-SiC. Due to the different butting of the SiC tetrahedron,
the SiC material shows a difference in cubic structure or hexagonal structure. As
shown in Fig. 4.20, the different butts of the SiC tetrahedron form the cubic and
hexagonal phases respectively [42].
The crystal form of hexagonal phase SiC substrate is the same as the group III
nitride. Thus, the hexagonal Si surface of SiC substrate is selected for epitaxial
growth of the nitride. Due to the polytype characteristics of SiC materials, the crystal
structure is more complex than the elemental semiconductors Si and Ge. The defects
in SiC can be very complex as well. So far, researchers have measured the distribution
Fig. 4.20 The cubic and hexagonal phases are respectively formed due to the different joint of the
SiC tetrahedrons [42]
65
Fig. 4.19 The regular
tetrahedron unit of SiC [40]
bonds, indicating that SiC has a structure with stabilized combination energy. This
is reflected by a high atomic energy value of 1250 kJ/mol. SiC has a high Debye
temperature of 1200–1400 K. Therefore, SiC has excellent mechanical and chemical
properties such as good stability, high hardness, wear resistance, and high melting
temperature under normal pressure.
The Si atomic layer and the C atomic layer in the single crystal SiC constitute
a basic diatomic layer. Si–C diatomic layers are alternately stacked in a certain
sequence to form SiC crystals. The difference in the stacking sequence of the diatomic
layers leads to different crystal structures, i.e., the formation of polyisomers of SiC,
or homogenous polymorphisms. More than 250 crystal structural morphologies have
been discovered [41]. The most important one are 3C, 2H, 4H, 6H, 8H, 9R, 10H,
14H, 15R, 20H, 21H, 24R, etc., belonging to three basic crystallography types:
cubic (C), hexagonal (H), diamond (R). Generally, the polytypes of hexagonal and
rhomboid structures are collectively referred to as α-SiC; the SiC of cubic structure is
collectively referred to as β-SiC. Due to the different butting of the SiC tetrahedron,
the SiC material shows a difference in cubic structure or hexagonal structure. As
shown in Fig. 4.20, the different butts of the SiC tetrahedron form the cubic and
hexagonal phases respectively [42].
The crystal form of hexagonal phase SiC substrate is the same as the group III
nitride. Thus, the hexagonal Si surface of SiC substrate is selected for epitaxial
growth of the nitride. Due to the polytype characteristics of SiC materials, the crystal
structure is more complex than the elemental semiconductors Si and Ge. The defects
in SiC can be very complex as well. So far, researchers have measured the distribution
Fig. 4.20 The cubic and hexagonal phases are respectively formed due to the different joint of the
SiC tetrahedrons [42]