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5 InGaN/GaN Multiple Quantum Wells Materials …
5.5.2 Semi-polar and Non-polar Materials
As shown in Fig. 5.5, both the (0001) Ga plane and the (000-1) N plane are c-plane in
the nitride semiconductors. The c-plane nitride material is a kind of polar material, in
which the surface of epitaxial material thin film is a polar surface. If the surface of the
film material is neither parallel nor perpendicular to the c-axis but an angle between
0° and 90°, the film is a semi-polar material. If the surface of the film material is the
m-plane or the a-plane parallel to the polar axis (i.e., the c-axis), the material has no
polarization effect along the growth direction, and the material is a nonpolar material
[33].
As shown in Fig. 5.6, non-polar and semi-polar GaN materials can be achieved by
epitaxy on a heterogeneous substrate with a specific crystal plane, e.g., a-plane GaN
grown on a r-plane sapphire substrate, a-plane and m-plane GaN grown on a-plane
Fig. 5.5 Polar, semi-polar and non-polar plane of wurtzite structure GaN
Fig. 5.6 Non-polar and semi-polar GaN materials grown on different epitaxial substrates