This document discusses gallium arsenide (GaAs), including its history, properties, manufacturing processes, applications, and cost. GaAs is a compound of gallium and arsenic atoms arranged in a cubic lattice. It has excellent electronic properties such as high electron mobility and saturated velocity. Its direct bandgap allows efficient light emission, making it useful for solar cells and optoelectronics. GaAs is manufactured through processes like Czochralski growth and epitaxy to produce wafers for devices. Though expensive, GaAs has applications in areas like wireless communication, satellites, and solar energy due to its high performance capabilities.

1. By:
Nhi Mai, Ricardo Lopez, Eric Leal,
Hector Leal Brol, James Lillian
ENGR2300 – Materials Engineering
November 2011

2.  Introduction
 History
 Properties
 Manufacturing Processes
 Cost
 Applications
 Conclusion

3.  Gallium Arsenide (GaAs)
is a combination of one
gallium atom (atomic no.
31) and one arsenic atom
(atomic no. 33). The
atoms are arranged in a
cubic sphalerite lattice. It
has a FCC symmetry. The
unit cell contains four
GaAs molecules. Gallium
atoms bond to four arsenic
and each arsenic atom
bonds to 4 gallium atoms.

4.  Elemental Gallium does
not occur naturally in
nature but in trace
amounts with bauxite and
zinc. It is a byproduct
during those ores’
processing. In its pure
form gallium is a soft,
brittle and silvery metallic
in color. Elemental gallium
melts slightly above room
temperature and will melt
in your hand.

5.  Arsenic is a highly toxic
element that is found
with many minerals,
especially sulfur, and
can be found naturally
as a pure substance.
Its main industrial use
is as a strengthener in
alloys with copper and
lead. Arsenic is also in
declining use in
pesticides and
herbicides.

6.  Dmitri Mendeleev
predicted all
elements’
properties on the
periodic table
 1875, Lecoq de
Boibaudran
discovered Gallium
in the Pyrenees
Mountains
 Method to retrieve
Gallium:
electrolysis

7.  Been known since
the Bronze Age
 1250, discovered
by Albert the Great
 Used as an
impurity in bronze
 Later found that
Arsenic was
poisonous
 Has symptoms that
were difficult to
distinguish

8.  Discovered by Victor
Goldschmidt
 First to combine these
elements
 1954, produced a large
amount for research on
use of this compound
 Since 1960s, used in
many devices such as
solar cells, light-emitting
diodes, lasers, and
optoelectronic devices

9.  Gallium, a poor metal, has atomic number 31 and it
is located in group 13, period 4, and block “p”. Its
mas is 69.72 amu, and has no electronegativity
according to Pauling.
 Arsenic, a metalloid, has atomic number 33 and it is
located in group 15, period 4, and block “p”. Its mas
is 74.92 amu, and has an electronegativity of 2.18
according to Pauling.

10. Electrical Properties
 Band gap (eV) = 1.42
 Electrical conductivity
1X10-6 (Ω*m)-1
 Electron mobility 7.7 m2 /
V*s
 Hole mobility .07 m2 / V*s
 Electron thermal velocity
4.4X105 m/s
 Hole thermal velocity
1.8X105 m/s
Thermal Properties
 GaAs has a thermal
conductivity of 0.55 W/cm-
C
 Melting point 1238 °C
 Specific heat 0.33 J g-1°C
-1
 Thermal diffusivity 0.31
cm2s-1
 Thermal expansion, linear
5.73X10-6 °C -1

11. The GaAs crystal is
composed of two
sublattices.
Each sublattice are face
centered cubic (fcc)
lattice.
They offset with respect
to each other by half the
diagonal of the fcc cube.
This crystal
configuration is known
as cubic sphalerite or
zinc blende.

12.  GaAs has basically
outdone silicon in
every imaginable
way due to its
incredible
characteristics.
 These
characteristics
make GaAs and
ideal candidate for
use in mobile
phones, satellite
communications,
microwave point-to-
point links, and
some radar
systems.
GaAs Properties
(Room
Temperature)

13. GaAs
 Higher saturated
electron velocity and
higher electron mobility.
 GaAs devices generate
less noise than silicon
and have higher
breakdown voltages.
 It has a direct bandgap
which means that it can
be used to emit light.
Silicon
 Considerably cheaper
than GaAs
 Existence of silicon
dioxide (one of the best
known insulators of any
kind)
 Posses a much higher
hole mobility which allows
for the construction of
higher-speed P-channel
field effect transistors.

14.  Ingot is a mold or cast of
a substance in bulk
quantity ex: gold bars
 Ingots can be grown 2
ways: Bridgman Method,
or Czochralski Method
 CM: Molten GaAs is
slowly pulled upwards
with a seed crystal while
cooling
 BM: melting pure GaAs
and cooling it from one
side. No pulling.
Centromax.net

15.  GaAs wafers are cut
from ingots.
 Requires mechanical
and chemical steps
such as etching,
cropping, thermal
treatment and
polishing.
 Single crystal wafers
are then used for
another process,
Epitaxy.

16.  Epitaxy- gowing a thin single
crystal layer over a single
crystal substrate
 Molecular Beam Epitaxy
(MBE)
 Molecular beams sending
molecules to the substrate
through a vacuum, substrate
is heated exciting molecules
eventually sticking to
substrate
 Metal Organic Vapor
Chemical Deposition
(MOVCD)
 Similar to MBE except layer
is formed by chemical
reactions rather than
physical placement

17. Expensive
Gallium is rare
Attempts to lower cost
by recycling
substrates or using
cheaper substrates
such as germanium or
silicon
Silicon max efficiency
25%
GaAs efficiency 30%

18.  Limit cost
 Improve integrated circuits in all
aspects of technologies.
 Due to its unique qualities, GaAs
can be used in computers, lasers,
solar cells, aerospace technology,
medical devices etc.

19. Solar panels consist of photovoltaic solar cells
Leading focus in respect to applying it to solar
cells
Used in photovoltaic solar cells for numerous
reasons:
– GaAs has a high absorption rate
– Very thin
– Records for highest efficiency (25%)
 Has a direct band gap, because of efficiency rate,
leads to shrinking of solar cell sizes thus reduction
in area
 Photovoltaic applications include:
– Satellites, cars, calculators highway signs

20. Projects such as the Rovers Spirit and
opportunity, which are exploring Mars’ surface,
have used GaAs for its solar cell power source
Radiation hardness. “Single effect events,”
(SEEs) associated with the transit of heavy ions
through semiconductor junctions have to be
minimized to reduce failure risk. Radiation
effects from particles can cause degradation,
and also failure of the electronic systems in
space vehicles or satellites
GaAs has promising future aerospace
applications in satellites, space crafts, signal
devices, sensors

21. Having a higher electron mobility, this allows
flow of electricity in transistors to flow much
faster and can lead to many future
applications such as:
– faster computers
– better wireless communication devices
Faster response times for transistors from
GaAs
Less propagation delay, less noise to date
using molecular beam epitaxial GaAs FETs

22.  GaAs power amplifiers operate at higher power
levels, have higher linearity and sharper edges,
can be operated at higher power levels because
they have higher breakdown voltages and allow
maximum channels to be used
 More efficient solar cells
 GaAs technologies allows to design at lower
frequencies, with less power consumption, over a
smaller area, providing a size and power
advantage to multi-function integrated solutions
for circuits and many more technologies

23.  Cost expensive, but hopefully will decrease over
the years
 GaAs has excellent electronic properties.
(It is superior to Silicon.)
 Powerful in the electronic industry:
 Aerospace
 Transistors
 Solar Cells