EPITAXY GROWTH TOPIC MADE BY- ASHISH JOSHI PONDHICHERRY UNIVERSITY DEPARTMENT OF ELECTRONICS ENGINEERING

1. HIGH SPEED SEMICONDUCTOR DEVICES:
TOPIC : EPITAXY
NAME: ASHISH JOSHI
ROLL NO: 21304025
SUBMITTED TO :DR. PROFESSOR K.ANUSUDHA MAM
BRANCH : ELECTRONICS AND COMMUNICATION ENGINEERING
COURSE: MTECH. 1ST YEAR
BATCH YEAR : 2021-2023
DEPARTMENT OF ELECTRONICS AND COMMUNICATION , PONDHICHERRY
UNIVERSITY

2. INTRODUCTION:
 Epitaxy refers to a type of crystal growth or material deposition in which new crystalline layers are formed
with one or more well-defined orientations with respect to the crystalline seed layer. The deposited
crystalline film is called an epitaxial film or epitaxial layer. The relative orientation(s) of the epitaxial layer to
the seed layer is defined in terms of the orientation of the crystal lattice of each material. For most epitaxial
growths, the new layer is usually crystalline and each crystallographic domain of the overlayer must have a
well-defined orientation relative to the substrate crystal structure.
 Epitaxy can involve single-crystal structures, although grain-to-grain epitaxy has been observed in granular
films. For most technological applications, single domain epitaxy, which is the growth of an overlayer
crystal with one well-defined orientation with respect to the substrate crystal, is preferred. Epitaxy can also
play an important role while growing superlattice structures.
 The term epitaxy comes from the Greek roots epi (ἐπί), meaning "above", and taxis (τάξις), meaning "an
ordered manner".

3. TYPES OF EPITAXIAL FILMS:
 Homoepitaxy is a kind of epitaxy performed with only one material, in which a crystalline film is
grown on a substrate or film of the same material. This technology is often 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“ .
 Homotopotaxy is a process similar to homoepitaxy except that the thin-film growth is not limited
to two-dimensional growth. Here the substrate is the thin-film material.
 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 crystals cannot otherwise be
obtained and to fabricate integrated crystalline layers of different materials.
 Heteroepitaxy occurs when a film of different composition and/or crystal structure than the
substrate is grown.

4. TYPES OF EPITAXIAL FILMS:
 Pendeo -epitaxy is a process in which the heteroepitaxial film is growing vertically and
laterally at the same time.
 Grain-to-grain epitaxy involves epitaxial growth between the grains of a multi crystalline
epitaxial and seed layer. This can usually occur when the seed layer only has an out-of-plane
texture but no in-plane texture. In such a case, the seed layer consists of grains with different
in-plane textures. The epitaxial overlayer then creates specific textures along each grain of the
seed layer, due to lattice matching. This kind of epitaxial growth doesn't involve single-crystal
films.

5. APPLICATIONS:
 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.
 In surface science, epitaxy is used to create and study monolayer and multilayer films of
adsorbed organic molecules on single crystalline surfaces.
 In contrast, surface defects and their geometry have significant influence on the adsorption of
organic molecules.
 Epitaxy is used in silicon-based manufacturing processes for bipolar junction transistors (BJTs)
and modern complementary metal–oxide–semiconductors (CMOS), but it is particularly
important for compound semiconductors such as gallium arsenide.

6. VAPOUR PHASE EPITAXY:
 Epitaxial silicon is usually grown using vapor-phase epitaxy (VPE), a modification of chemical vapor
deposition. Molecular-beam and liquid-phase epitaxy (MBE and LPE) are also used, mainly for compound
semiconductors. Solid-phase epitaxy is used primarily for crystal-damage healing.
 Vapor-phase:
 Silicon is most commonly deposited by doping with silicon tetrachloride and hydrogen at approximately
1200 to 1250 °C
 SiCl4(g) + 2H2(g) ↔ Si(s) + 4HCl(g)
 where (g) and (s) represent gas and solid phases, respectively. This reaction is reversible, and the growth
rate depends strongly upon the proportion of the two source gases. Growth rates above 2 micrometres per
minute produce polycrystalline silicon, and negative growth rates (etching) may occur if too much
hydrogen chloride byproduct is present. (In fact, hydrogen chloride may be added intentionally to etch the
wafer.) An additional etching reaction competes with the deposition reaction:
 SiCl4(g) + Si(s) ↔ 2SiCl2(g)

7. REPRESENTATION OF VAPOUR PHASE
EPITAXY:

8. LIQUID 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 relatively fast and uniform. The most used substrate
is indium phosphide (InP). Other substrates like glass or ceramic can be applied for special
applications. To facilitate nucleation, and to avoid tension in the grown layer the thermal
expansion coefficient of substrate and grown layer should be similar.
 Centrifugal liquid-phase epitaxy is used commercially to make thin layers of silicon,
germanium, and gallium arsenide. Centrifugally formed film growth is a process used to form
thin layers of materials by using a centrifuge. The process has been used to create silicon for
thin-film solar cells and far-infrared photodetectors. Temperature and centrifuge spin rate are
used to control layer growth. Centrifugal LPE has the capability to create dopant
concentration gradients while the solution is held at constant temperature.

9. REPRESENTATION OF LIQUID EPITAXY:

10. MOLECULAR BEAM EPITAXY:
 In molecular beam epitaxy (MBE), a source material is heated to produce an evaporated beam
of particles. These particles travel through a very high vacuum (10−8 Pa; practically free space)
to the substrate, where they condense. MBE has lower throughput than other forms of
epitaxy. This technique is widely used for growing periodic groups III, IV, and V semiconductor
crystals.
 MBE systems can also be modified according to need. Oxygen sources, for example, can be
incorporated for depositing oxide materials for advanced electronic, magnetic and optical
applications, as well as for fundamental research.

11. DOPING:
 An epitaxial layer can be doped during deposition by adding impurities to the source gas,
such as arsine, phosphine, or diborane.
 The concentration of impurity in the gas phase determines its concentration in the deposited
film. As in chemical vapor deposition (CVD), impurities change the deposition rate.
 Additionally, the high temperatures at which CVD is performed may allow dopants to diffuse
into the growing layer from other layers in the wafer ("out-diffusion"). Also, dopants in the
source gas, liberated by evaporation or wet etching of the surface, may diffuse into the
epitaxial layer ("autodoping").
 The dopant profiles of underlying layers change as well, however not as significantly.

12. Advantages of Epitaxy:
 The use of epitaxial growth, therefore reduces the growth time, wafering
cost and eliminates the wastages caused during growth, cutting, polishing
etc. The major advantage of the epitaxy is the uniformity in the
composition, controlled growth parameters and better understanding of
the growth itself.
Disadvantages of Epitaxy:
 For overall perfect and pure film, it is necessary to maintain a very low
pressure of the order of 10-10 Torr which is slightly difficult.
 This process is very expensive as compared to CVD process.

13. THANK YOU
WITH REGARDS
ASHISH JOSHI