Lecture 30: Kinetics of Epitaxial Growth: Surface Diffusion and
Nucleation
Today’s topics
• Understanding the basics of epitaxial techniques used for surface growth of crystalline
structures (films, or layers).
• The kinetics of epitaxial growth is determined by the surface diffusion and nucleation.
• Understanding the three thermodynamic modes of epitaxial growth: competition between the
three interface energies.
Basics of Epitaxial Growth:
• Epitaxy refers to the method of depositing a mono-crystalline film on a mono-crystalline substrate.
The deposited film is denoted as epitaxial film or epitaxial layer. The term epitaxy comes from the
Greek roots --- epi, meaning "above", and taxis, meaning "in ordered manner". So, “epitaxial” can be
translated "to arrange upon".
growing film
1D View:
substrate
• Epitaxial films may be grown from gaseous or liquid precursors. Because the substrate acts as a seed
crystal, the deposited film takes on a lattice structure and orientation identical to those of the substrate.
This is different from other thin-film deposition methods which deposit polycrystalline or amorphous
films, even on single-crystal substrates.
• Epitaxial films can be classified into two categories: homoepitaxy, for which the film is deposited on a
substrate of the same composition; and heteroepitaxy, for which the film is deposited on a substrate of
different.
• Homoepitaxy is a kind of epitaxy performed with only one material. In homoepitaxy, a crystalline film
is grown on a substrate or film of the same material. This technology is used to grow a film which is
more pure than the substrate and to fabricate layers having different doping levels. In academic
literature, homoepitaxy is often abbreviated to "homoepi".
• Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In
heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material. This
technology is often used to grow crystalline films of materials for which single crystals cannot
1
, otherwise be obtained and to fabricate integrated crystalline layers of different materials. Examples
include gallium nitride (GaN) on sapphire or aluminum gallium indium phosphide (AlGaInP) on
gallium arsenide (GaAs).
Applications of Epitaxial Growth:
• Epitaxy is used in nanotechnology and in semiconductor fabrication. Indeed, epitaxy is the only
affordable method of high quality crystal growth for many semiconductor materials, including
technologically important materials as silicon-germanium, gallium nitride, gallium arsenide, indium
phosphide and graphene.
• Epitaxy is also used to grow layers of pre-doped silicon on the polished sides of silicon wafers, before
they are processed into semiconductor devices. This is typical of power devices, such as those used in
pacemakers, vending machine controllers, automobile computers, etc.
• Recently, epitaxy has been used to deposit organic molecules onto crystalline substrate to form
organized layer molecular electronics!
Ag(111) surface by STM, 13X13 nm, T:5K
2
Nucleation
Today’s topics
• Understanding the basics of epitaxial techniques used for surface growth of crystalline
structures (films, or layers).
• The kinetics of epitaxial growth is determined by the surface diffusion and nucleation.
• Understanding the three thermodynamic modes of epitaxial growth: competition between the
three interface energies.
Basics of Epitaxial Growth:
• Epitaxy refers to the method of depositing a mono-crystalline film on a mono-crystalline substrate.
The deposited film is denoted as epitaxial film or epitaxial layer. The term epitaxy comes from the
Greek roots --- epi, meaning "above", and taxis, meaning "in ordered manner". So, “epitaxial” can be
translated "to arrange upon".
growing film
1D View:
substrate
• Epitaxial films may be grown from gaseous or liquid precursors. Because the substrate acts as a seed
crystal, the deposited film takes on a lattice structure and orientation identical to those of the substrate.
This is different from other thin-film deposition methods which deposit polycrystalline or amorphous
films, even on single-crystal substrates.
• Epitaxial films can be classified into two categories: homoepitaxy, for which the film is deposited on a
substrate of the same composition; and heteroepitaxy, for which the film is deposited on a substrate of
different.
• Homoepitaxy is a kind of epitaxy performed with only one material. In homoepitaxy, a crystalline film
is grown on a substrate or film of the same material. This technology is used to grow a film which is
more pure than the substrate and to fabricate layers having different doping levels. In academic
literature, homoepitaxy is often abbreviated to "homoepi".
• Heteroepitaxy is a kind of epitaxy performed with materials that are different from each other. In
heteroepitaxy, a crystalline film grows on a crystalline substrate or film of a different material. This
technology is often used to grow crystalline films of materials for which single crystals cannot
1
, otherwise be obtained and to fabricate integrated crystalline layers of different materials. Examples
include gallium nitride (GaN) on sapphire or aluminum gallium indium phosphide (AlGaInP) on
gallium arsenide (GaAs).
Applications of Epitaxial Growth:
• Epitaxy is used in nanotechnology and in semiconductor fabrication. Indeed, epitaxy is the only
affordable method of high quality crystal growth for many semiconductor materials, including
technologically important materials as silicon-germanium, gallium nitride, gallium arsenide, indium
phosphide and graphene.
• Epitaxy is also used to grow layers of pre-doped silicon on the polished sides of silicon wafers, before
they are processed into semiconductor devices. This is typical of power devices, such as those used in
pacemakers, vending machine controllers, automobile computers, etc.
• Recently, epitaxy has been used to deposit organic molecules onto crystalline substrate to form
organized layer molecular electronics!
Ag(111) surface by STM, 13X13 nm, T:5K
2
