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All the commercial semiconducting light-emitting diodes (LEDs) and laser diodes (LDs) are currently made of III-V compound thin films produced by the metalorganic chemical vapor deposition (MOCVD) technique. These III-V compounds can be grouped into the families of the antimonides, arsenides, phosphides and nitrides. The first three have mainly a cubic lattice structure, while the nitrides have a hexagonal lattice structure.
The materials in LEDs need superior electronic properties and high light emission efficiencies by eliminating the crystalline perfection such as stacking faults and dislocations. Defect degradation in LEDs is dominated by the motion of dislocations in the active region with the creation of the so-called dark-line defects.
Figure 2244 shows bandgap and chemical bond length for semiconductors used in visible LEDs (light emitting devices).
Figure 2244. Bandgap and chemical bond length for semiconductors used in visible LEDs (light emitting devices). Adapted from [1]
Table 2244 shows the lattice mismatch (%) between the substrates and epitaxial layers, and the resulting misfit dislocation separation (in Å) corresponding to complete misfit relaxation for the basal plane interfaces.
Table 2244. The lattice mismatch (%) between the substrate and epitaxial layers, and the resulting misfit dislocation separation (in Å).
Crystalline Properties |
|
6H-SiC |
α-A1203 |
InN |
AlN |
GaN |
Lattice mismatch with |
Sapphire |
11.5% |
-- |
25.4% |
12.5% |
14.8% |
SiC
|
-- |
-11.5% |
14.0%
|
1.0%
|
3.3% |
GaN |
-3.3% |
-14.8% |
10.6% |
-2.4% |
-- |
Dislocation distance on |
Sapphire |
21.9 |
-- |
10.6 |
20.3 |
17.2 |
SiC |
-- |
21.9 |
20.4 |
276.7 |
80.9 |
GaN |
80.9 |
17.2 |
27.3 |
114.4 |
-- |
[1] Ponce, F. A. and Bour, D.P., Nature, 386, (1997) 351.
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