4.3 Group III Nitride LED Epitaxial Technology
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4.3.2 MBE Method
MBE is an abbreviation for Molecular Beam Epitaxy, which is a technique for growth
of high quality crystal films on a substrate. The material vapor under ultra-high
vacuum conditions, which is generated by heating the boat containing various desired
components and is collimated, become molecular beam or atomic beam. The beams
are directly sprayed onto a substrate. Simultaneously controlling the molecular beam
to scan the substrate, the molecules or atoms can be grown on the substrate to form
a thin film. The advantages of this technology are: (1) the substrate temperature is
low; (2) the growth rate of the film is low; (3) the beam intensity is easy to control,
and (4) the film composition and doping concentration can be quickly adjusted as the
source changes. With this technique, it is possible to prepare a single crystal film as
thin as several tens of atomic layers. An ultrathin layer quantum well microstructure
material can be grown by alternately growing different compositions and doped thin
films.
The characteristics of MBE include: (1) The growth rate is extremely slow, about
1 m/hr, which is equivalent to grow a single atomic layer per second. This facilitates
the precise control of thickness, structure and composition, and formation of steep
heterostructures. In fact, MBE is an atomic processing technology. It is particularly
suitable for growing superlattice materials. (2) The temperature of epitaxial growth
is low. This thereby reduces the lattice mismatch effect introduced by thermal expansion at the interface and the effect of substrate impurities on the self-doping diffusion
of the epitaxial layer. (3) Since the growth is carried out in an ultra-high vacuum, the
surface of the substrate can be completely cleaned by treatment. The contamination
can be avoided during the epitaxial process so that an excellent quality epitaxial layer
can be grown. Generally, there is in situ instrument in molecular beam epitaxy for
detecting surface structure, composition and vacuum residual gas. The composition
and structural integrity of the epitaxial layer can be monitored at any time, which is
beneficial to scientific research. (4) MBE is a dynamic process of growing incident
neutral particles (atoms or molecules) one-by-one on a substrate rather than a thermodynamic process. It can therefor grow films that are difficult to grow according
to ordinary thermal equilibrium growth methods. (5) MBE is an ultra-high vacuum
physical deposition process that does not require intermediate chemical reactions
and is not affected by mass transfer. The use of shutters can also instantaneously
control and interrupt the growth process. Therefore, the composition and doping
concentration of the film can be rapidly adjusted as the source changes.
4.3.3 MOCVD Method
Metal Organic Chemical Vapor Deposition (MOCVD) was developed by Amano
et al. [3] in 1968 to prepare a compound semiconductor single crystal thin film
material. It is a chemical vapor deposition technology widely used in compound
39
4.3.2 MBE Method
MBE is an abbreviation for Molecular Beam Epitaxy, which is a technique for growth
of high quality crystal films on a substrate. The material vapor under ultra-high
vacuum conditions, which is generated by heating the boat containing various desired
components and is collimated, become molecular beam or atomic beam. The beams
are directly sprayed onto a substrate. Simultaneously controlling the molecular beam
to scan the substrate, the molecules or atoms can be grown on the substrate to form
a thin film. The advantages of this technology are: (1) the substrate temperature is
low; (2) the growth rate of the film is low; (3) the beam intensity is easy to control,
and (4) the film composition and doping concentration can be quickly adjusted as the
source changes. With this technique, it is possible to prepare a single crystal film as
thin as several tens of atomic layers. An ultrathin layer quantum well microstructure
material can be grown by alternately growing different compositions and doped thin
films.
The characteristics of MBE include: (1) The growth rate is extremely slow, about
1 m/hr, which is equivalent to grow a single atomic layer per second. This facilitates
the precise control of thickness, structure and composition, and formation of steep
heterostructures. In fact, MBE is an atomic processing technology. It is particularly
suitable for growing superlattice materials. (2) The temperature of epitaxial growth
is low. This thereby reduces the lattice mismatch effect introduced by thermal expansion at the interface and the effect of substrate impurities on the self-doping diffusion
of the epitaxial layer. (3) Since the growth is carried out in an ultra-high vacuum, the
surface of the substrate can be completely cleaned by treatment. The contamination
can be avoided during the epitaxial process so that an excellent quality epitaxial layer
can be grown. Generally, there is in situ instrument in molecular beam epitaxy for
detecting surface structure, composition and vacuum residual gas. The composition
and structural integrity of the epitaxial layer can be monitored at any time, which is
beneficial to scientific research. (4) MBE is a dynamic process of growing incident
neutral particles (atoms or molecules) one-by-one on a substrate rather than a thermodynamic process. It can therefor grow films that are difficult to grow according
to ordinary thermal equilibrium growth methods. (5) MBE is an ultra-high vacuum
physical deposition process that does not require intermediate chemical reactions
and is not affected by mass transfer. The use of shutters can also instantaneously
control and interrupt the growth process. Therefore, the composition and doping
concentration of the film can be rapidly adjusted as the source changes.
4.3.3 MOCVD Method
Metal Organic Chemical Vapor Deposition (MOCVD) was developed by Amano
et al. [3] in 1968 to prepare a compound semiconductor single crystal thin film
material. It is a chemical vapor deposition technology widely used in compound