4. Epitaxy is the process of growing a thin crystalline layer on a crystalline
Epitaxial layer is always thinner than the substrate
Epitaxial grow techniques:
What is epitaxy?
Vapor-Phase Epitaxy Liquid Phase-Epitaxy Molecular Beam Epitaxy
VPE is a modification of chemical vapor
LPE is a method to grow semiconductor
crystal layers from the melt on solid
MBE is based on an UHV(Ultra High
Chemical reactions involved Chemical reactions involved No chemical reactions involved.
The deposition substrate is the same material as we are depositing from the beam.
(e.g Si on Si)
Substrate and material are of different composition in order to fabricate integrated
crystalline layers of different materials. (e.g GaAs on Si)
6. There are three main growth modes that can occur depending upon the
substrate temperature, the deposition rate and available surface energy
8. • Pumping Systems
• Growth Chamber, epitaxial growth
• Load lock facilitates the
introduction and removal of
• Auxiliary chamber host analytical
and process equipment
9. Gas sources are heated in separate k-cells or
electron beam evaporators to achieve
molecular or atom beams.
No interaction with each other until they
reach the Surface.
During the deposition, the interactions of the
atoms produce the epitaxial growth.
MBE Growth process
10. Controlling , via shutters and the
temperature of the source, will
control the rate of impinging
The temperature of the substrate will
control the rate of diffusion and
Background gases help to avoid
MBE Growth process
11. Deposition rate (𝜇𝑚/ℎ𝑟): 1-5 s
Growth temperature (℃): 550
Thickness control (Å): 5
Interface width (Å): 5
Shuttering control: 0.1 s
12. Reflection High Energy Electron Diffraction (RHEED)
Observe removal of contaminants from the substrate surface
Calibrate growth rates
Estimate the substrate temperature
Determine the stoichiometry
Analyze surface morphology – RHEED pattern
Study growth kinetics – RHEED intensity oscillations
In Situ Monitoring
14. Materials used on MBE
Different materials are used depending the type of MBE, but we will focus on
Solid Source MBE type.
Molecular Beams Substrate target
Group III – V molecular beams III-V Semiconductors
Group II – VI molecular beams II-VI Semiconductors
Others IV-VI Semiconductors, Heusler alloys,
silicides, metals ...
Typically, the substrate target is a semiconductor material with useful electronic properties.
The molecular beam quite often is composed of evaporated elemental substances such as
gallium and arsenic
15. Materials used on MBE
III-V semiconductors offer high
electron mobility and a direct high
II-VI semiconductors exhibit direct
large band gaps , but have some
problems with conductivity.
IV – VI Semiconductors also offer a
narrow band gap.
17. Clean surfaces.
Monitoring in situ.
Independent vaporization of each
Multiple sources are used to grow
alloy films and heterostructures.
Deposition is controlled at
Extremely flexible technique since
growth parameters are varied
Benefits/Problems of MBE
Very low deposition rates: 1um –
100nm per hour are used.
High equipment cost and long set
Extreme Flexibility (uncontrolled
flexibility = chaos!).
Many Boring Evenings!
Mostly Broken Equipment!
21. Very well controlled and clean result.
High equipment cost and long setup time
In situ monitoring
High Speed electronic and optoelectronic applications
III-V semiconductors as GaAs are the most common used in Electronic
and OptoElectronics devices.