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Professor, Department of Electrical Engineering,
Laser Technology Program,
Indian Institute of Technology, Kanpur
Prof. Utpal Das
http://www.iitk.ac.in/ee/faculty/det_resume/utpal.html
Lecture 8: Epitaxial growth - I
(Techniques)
Semiconductor Optical Communication
Components and Devices
Synthesis & Processing: Much of the processing and synthesis of semiconductor
lasers parallels that used in conventional Integrated Circuits.
Patterning, as in IC’s, is done primarily through
photolithography. Ion implantation and metallization are also
similar to that in IC’s, but different temperature constraints and
material properties of GaAs or InP.
A more significant departure is required for growing thin
epitaxial alloy films often required for compound semiconductor
devices. Techniques such as Liquid Phase Epitaxy (LPE),
Molecular Beam Epitaxy (MBE), and Metal-Organic Chemical
Vapor Deposition (MOCVD) are employed in growing epitaxial
heterostructures for compound materials including GaAs,
AlGaAs, InGaAs, InP, InGaAsP, etc. For Si mostly VPE is used.
EPITAXY: Epi (top)-Taxis (to deposit)
Growing a crystalline layer over a crystalline substrate.
Overview of the competing technologies
Epitaxial Growth Techniques
Epitaxial Growth (CBE)
LPE VPE MBE MOCVD CBE
A)Excellent
Quality,
Simple
Setup.
A)Quality not
great but
moderate,
Rugged
A)Extremely
narrow Layers,
Quality is good,
Characterizing
instruments can
be mounted on the
chamber.
A)Good
Quality not as
thin a layer as
MBE but close,
Infinite Source
A)Best
compromise
between MBE &
MOCVD
B)Thin
Structure is
not possible.
Surface
uneven.
B)High
temperature
Growth.
Sharp
interfaces not
possible.
B) Expensive,
Limited Source,
Not production
oriented.
P Compounds very
difficult.
B) Highly toxic
gases,
Precautions
needed
B) Expensive,
Carbon
Contamination,
Not many
Disadvantages.
example, one bin might hold gallium (Ga), another aluminum (Al), and another
gallium arsenide (GaAs). The substrate is placed in contact with each bin in turn,
the temperature is reduced, and an exact thickness of material is crystallized.
A crystalline layer of material is
grown from a saturated liquid
solution. The process takes place
in a high-purity carbon boat, which
contains the substrate in the lower
part and a series of bins with
melted materials in each bin. For
Liquid-Phase Epitaxy (LPE)H2
H2
Thermocouple
Mo Push Rod
Furnace HeaterFurnace
Control
Mo Fixed Rod
Gasket Seal
O-Ring Seal
Quartz
Growth Furnace
Temperature ramp
Mo Push
Rod
Graphite
Crucible
SubstrateGraphite
Substrate
Carrier
Etch and Growth
Solution Liquids Graphite
Cover
Typical VPE Epitaxial Growth systems
Gas Showerhead
SubstratesGas Inlet
Carrousel
Water cooled
RF Induction
Heating
Pumped
Gas Outlet
Carrousel
rotation
In vapor-phase epitaxy (VPE), the material to be deposited is
transported as part of a gaseous compound, a halogen such as gallium chloride
(GaCl3), or an organometallic compound, such as trimethyl gallium
[(CH3)3Ga]. When the vapor touches the substrate, it reacts, depositing the
material to grow the crystal. When the vapor touches the substrate, it reacts,
depositing the material to grow the crystal.
VPE
Kinetics of Growth for III-V compounds
Inverse Temperature
Gro
wth
Rate
(L
og)
Limited
By
Chemical
Kinetics
Mass
Transport
LimitedDesorption
~ 1/500~ 1/850
Review questions
1. Which system should one use for the growth of InxGa(1-x)AsyP(1-y) ?
What are the disadvantages of this growth system?
2. Why is VPE system not popular for the growth of InxGa(1-x)AsyP(1-y)
communication device applications?
3. Which growth system is suitable for obtaining highest quality
material ? What are the disadvantages of this system?
4. How should one select the growth temperature for a particular
semiconductor?
5. Between MBE and MOCVD, which is more suitable in obtaining
better electronic devices (Should have less non-compensated
unintentional doping)
6. Which growth system should one choose if both optical devices and
electronic devices are to be integrated on the same chip?
