Epitaxy is the process of depositing a mono-crystalline film on a mono-crystalline substrate, classified into homoepitaxy, heteroepitaxy, and their pseudo variants. Various methods such as liquid phase epitaxy and molecular beam epitaxy are utilized for this process, each offering specific advantages like high growth rates and controlled film thickness, while also presenting limitations such as reproducibility issues and high costs. Applications include semiconductor fabrication, nanotechnology, and producing high-quality crystal layers.

1. PRESENTED BY:
RUCHI SHARMA:14105A0007
RUTUJA SOLKAR:14105A0008

2. •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 means “above” and taxis means
“deposition in ordered manner”.
•Epitaxial films may be grown from gaseous or
liquid precursors.
•The substrate acts as a seed crystal, the
deposited film takes on a lattice structure
and orientation identical to those of the
substrate.

3. Types of Epitaxial films
Epitaxial films can be classified into two broad categories:
Homoepitaxy
-The film and the substrate are the same material.
-Epitaxially grown layers are purer than the substrate and can
be doped independently o f it.
Pseudo-homoepitaxy: Epi film and substrate are of same material
but doping in epi layer can be different from that of substrate
(doped Si/undoped Si)
Heteroepitaxy-
Film and substrate are of different materials
Pseudo heteroepitaxy : chemical commonality between film and
substrate

4. Applications of Epitaxial Growth
• Nanotechnology
• semiconductor fabrication
• high quality crystal growth(silicon –germanium, gallium-nitride)
• to grow layers of pre-doped silicon (in pacemakers, vending
machine)
•To deposit organic molecules onto crystalline substrate.

5. Liquid Phase Epitaxy
• Liquid phase epitaxy (LPE) is a method to grow semiconductor crystal
layers from the melt on solid substrates
• This happens at temperatures well below the melting point of the
deposited semiconductor
• The semiconductor is dissolved in the melt of another material. At
conditions that are close to the equilibrium between dissolution and
deposition the deposition of the semiconductor crystal on the substrate is
slowly and uniform
• The equilibrium conditions depend very much on the temperature and
on the concentration of the dissolved semiconductor in the melt

6. ADVANTAGES
• High growth rates. These are typically
0.1–10μm/h, i.e. faster than in VPE or
MBE
• Favorable segregation of impurities into
the liquid phase
• Ability to produce very flat surfaces and
excellent structural perfection
• Wide selection of dopants
• Growth can be made to occur over a
wide range of temperatures
• Absence of highly toxic precursors or
byproducts.
LIMITATIONS
• To control of layer thickness, alloy
compositions,doping,interface
smoothness and difficulties in growing
certain combinations of interest for hetero
structure devices.
• Poor reproducibility, problems with
scaling up in size or throughput

7. • Atomic layer deposition (ALD) is a thin film deposition technique
that is based on the sequential use of a gas phase chemical process
• ALD is considered a subclass of chemical vapour deposition. The
majority of ALD reactions use two chemicals, typically
called precursors
• These precursors react with the surface of a material one at a time in
a sequential, self-limiting, manner
• Through the repeated exposure to separate precursors, a thin film is
slowly deposited

8. Advantages
• VPE provides a very controlled method to produce a film to an
atomically specified thickness. Also, the growth of different multilayer
structures is straightforward.
• Due to the sensitivity and precision of the equipment, it is very
beneficial to those in the field of microelectronics and nanotechnology
in producing small, but efficient semiconductors
Disadvantages
• High purity of the substrates is very important, and as such, high costs
will ensue
• Once the layer has been made and the process is complete, there may
be a requirement of needing to remove excess precursors from the
final product

9. • To make an interesting new crystal using MBE, you start off with a base material
called a substrate, which could be a familiar semiconductor material such as silicon,
germanium, or gallium arsenide
• First, you heat the substrate, typically to some hundreds of degrees (for example,
500–600°C or about 900–1100°F in the case of gallium arsenide)
• Then you fire relatively precise beams of atoms or molecules (heated up so they're
in gas form) at the substrate from "guns" called effusion cells
• The molecules land on the surface of the substrate, condense, and build up very
slowly and systematically in ultra-thin layers, so the complex, single crystal you're
after grows one atomic layer at a time
• That's why MBE is an example of what's called thin-film deposition
Molecular Beam Epitaxy

10. • Basic elements of MBE
system:
• Heated substrate
• Effusion cells and shutter
• Reflection High Energy
Electron
• Diffraction (RHEED system-
RHEED gun & screen)
• Ultra High Vacuum (UHV)
• Liquid Nitrogen cryopanelling

11. • The solid source material sublimates
• They provide angular distribution of atoms or molecules in beam
• The substrate is heated to the necessary temperature
• The gaseous elements then condense on the wafer where they may
react with each other to form a layer
• Atoms on clean surface are free to move until
finding correct position in the crystal
lattice to bond

12. Advantages:
It's particularly good for making high-quality (low-defect, highly uniform)
semiconductor crystals from compounds or from a number of different
elements, instead of from a single element
It also allows extremely thin films to be fabricated in a very precise, carefully
controlled way
Disadvantages:
It's a slow and laborious method (crystal growth rate is typically a few microns
per hour), which means it's more suited for scientific research laboratories than
high-volume production, and the equipment involved is complex and very
expensive (partly because of the difficulty of achieving such clean, high-
vacuum conditions)
Advantages and
Disadvantages of MBE