A Presentation on Molecular Beam Epitaxy for college students . BTech 3rd Year Electronics and Communication Branch. Helping the students to make them free to do something productive rather than wasting time PPTs

1. DEPARTMENT OF ELECTRONICS AND
COMMUNICATION ENGINEERING
Molecular Beam Epitaxy
Presented By:
Aditya Kumar (1809731012)
Guided By:
Mr. Gaurav Mehra

2. Outline
 What is Epitaxy ?
Types of Epitaxy
Appratus for Epitaxy
Molecular Beam Epitaxy (MBE)
Advantages of MBE doping

3. What is
Epitaxy?
• The term Epitaxy means “arranged upon”.
Epi : “upon” and
Taxies: “ordered”
• Basically deals with the ordered placement of
atoms, carefully, on the surface of a substrate.
• Substrate acts ass a seed crystal.

4. Types of
Epitaxy
Epitaxy having two Types:
Homoepitaxy : Overgrowth of a layer of same material
such as silicon grown on silicon.
Hetroepitaxy : Material grown on substrate is of
different material.

5. Apparatus for
Epitaxy
There are a number of methods to achieve epitaxial growth these
are :
• Vapour phase epitaxy (VPE)
SiCl4+2H2 Si+4HCl (1200C)
•Liquid phase epitaxy (LPE)
Growth of epitaxial layers on crystalline substrates by direct
precipitation from the liquid phase. This technique is mainly
used for growing gallium arsenide and other III-V compunds.
• Molecular beam epitaxy (MBE)
1) Uses an evaporation method
2) MBE is also a low temperature process
3) In MBE Substrate is held in a high vacuum while molecular
or atomic beams of the constituents impinge upon its
surface.

6. Molecular
Beam Epitaxy
(MBE)
This process is used to achieve precise control of chemical
compositions and doping profiles.
Fig. Schematic Diagram of MBE System

7. Molecular
Beam Epitaxy
(MBE)
 Uses vacuum evaporation technique to grow epi-taxial
layers with very high degree of control.
 A conventional temperature range for MBE is from 400 to
800 degree C.
 Growth rates in the range 0.10 to 0.3um/min
 High temperature baking between 1000-1200 degree C
decomposes the nature oxide.
 Growth process can be better understood by studying the
kinetic theory of gases in a vacuum system.
 Beams are thermally generated effusion cells
Temperature is accurately controlled to maintain the
required intensity of the beam

8. Molecular
Beam Epitaxy
(MBE)
Fig. Schematic of practical MBE system

9. Molecular
Beam Epitaxy
(MBE)
 Molecular beam epitaxy systems are very expensive
 The quality of the films is very good with precise control
of doping.
 Again vacuum system is an important part of the
apparatus.
 The condensation of the source molecules takes place at
the substrate is at a lower temperature.
 For monitoring the whole process sophisticated
analytical techniques are used.

10. Advantages of
MBE Doping
 MBE doping is not affected by time constant
consideration.
 More control of doing profile is possible.
 MBE is not complicated by boundary layer effect as in
CVD process.
 MBE is very adaptable to ion-implant doping due to its
vacuum process.
 MBE is a low temperature processing.

11. Thank You !