<s>
Metalorganic	B-Algorithm
vapour-phase	I-Algorithm
epitaxy	I-Algorithm
(	O
MOVPE	B-Algorithm
)	O
,	O
also	O
known	O
as	O
organometallic	O
vapour-phase	O
epitaxy	O
(	O
OMVPE	B-Algorithm
)	O
or	O
metalorganic	B-Algorithm
chemical	I-Algorithm
vapour	I-Algorithm
deposition	I-Algorithm
(	O
MOCVD	B-Algorithm
)	O
,	O
is	O
a	O
chemical	B-Algorithm
vapour	I-Algorithm
deposition	I-Algorithm
method	O
used	O
to	O
produce	O
single	O
-	O
or	O
polycrystalline	O
thin	O
films	O
.	O
</s>
<s>
In	O
contrast	O
to	O
molecular-beam	B-Algorithm
epitaxy	I-Algorithm
(	O
MBE	O
)	O
,	O
the	O
growth	O
of	O
crystals	O
is	O
by	O
chemical	O
reaction	O
and	O
not	O
physical	O
deposition	O
.	O
</s>
<s>
This	O
takes	O
place	O
not	O
in	O
vacuum	B-General_Concept
,	O
but	O
from	O
the	O
gas	O
phase	O
at	O
moderate	O
pressures	O
(	O
10	O
to	O
760Torr	O
)	O
.	O
</s>
<s>
In	O
MOCVD	B-Algorithm
ultrapure	O
precursor	O
gases	O
are	O
injected	O
into	O
a	O
reactor	O
,	O
usually	O
with	O
a	O
non-reactive	O
carrier	O
gas	O
.	O
</s>
<s>
As	O
the	O
precursors	O
approach	O
the	O
semiconductor	B-Architecture
wafer	I-Architecture
,	O
they	O
undergo	O
pyrolysis	O
and	O
the	O
subspecies	O
absorb	O
onto	O
the	O
semiconductor	B-Architecture
wafer	I-Architecture
surface	O
.	O
</s>
<s>
In	O
the	O
mass-transport-limited	O
growth	O
regime	O
in	O
which	O
MOCVD	B-Algorithm
reactors	O
typically	O
operate	O
,	O
growth	O
is	O
driven	O
by	O
supersaturation	O
of	O
chemical	O
species	O
in	O
the	O
vapor	O
phase	O
.	O
</s>
<s>
MOCVD	B-Algorithm
can	O
grow	O
films	O
containing	O
combinations	O
of	O
group	O
III	O
and	O
group	O
V	O
,	O
group	O
II	O
and	O
group	O
VI	O
,	O
group	O
IV	O
.	O
</s>
<s>
The	O
diffusion	O
of	O
atoms	O
on	O
the	O
substrate	B-Architecture
surface	O
is	O
affected	O
by	O
atomic	O
steps	O
on	O
the	O
surface	O
.	O
</s>
<s>
The	O
vapor	O
pressure	O
of	O
the	O
group	O
III	O
metal	O
organic	O
source	O
is	O
an	O
important	O
control	O
parameter	O
for	O
MOCVD	B-Algorithm
growth	O
,	O
since	O
it	O
determines	O
the	O
growth	O
rate	O
in	O
the	O
mass-transport-limited	O
regime	O
.	O
</s>
<s>
In	O
the	O
metal	B-Algorithm
organic	I-Algorithm
chemical	I-Algorithm
vapor	I-Algorithm
deposition	I-Algorithm
(	O
MOCVD	B-Algorithm
)	O
technique	O
,	O
reactant	O
gases	O
are	O
combined	O
at	O
elevated	O
temperatures	O
in	O
the	O
reactor	O
to	O
cause	O
a	O
chemical	O
interaction	O
,	O
resulting	O
in	O
the	O
deposition	O
of	O
materials	O
on	O
the	O
substrate	B-Architecture
.	O
</s>
<s>
A	O
substrate	B-Architecture
sits	O
on	O
a	O
susceptor	O
which	O
is	O
at	O
a	O
controlled	O
temperature	O
.	O
</s>
<s>
The	O
susceptor	O
is	O
made	O
from	O
a	O
material	O
resistant	O
to	O
the	O
temperature	O
and	O
metalorganic	O
compounds	O
used	O
,	O
often	O
it	O
is	O
machined	O
from	O
graphite	B-Application
.	O
</s>
<s>
For	O
growing	O
nitrides	O
and	O
related	O
materials	O
,	O
a	O
special	O
coating	O
,	O
typically	O
of	O
silicon	O
nitride	O
or	O
tantalum	O
carbide	O
,	O
on	O
the	O
graphite	B-Application
susceptor	O
is	O
necessary	O
to	O
prevent	O
corrosion	O
by	O
ammonia	O
(	O
NH3	O
)	O
gas	O
.	O
</s>
<s>
One	O
type	O
of	O
reactor	O
used	O
to	O
carry	O
out	O
MOCVD	B-Algorithm
is	O
a	O
cold-wall	O
reactor	O
.	O
</s>
<s>
In	O
a	O
cold-wall	O
reactor	O
,	O
the	O
substrate	B-Architecture
is	O
supported	O
by	O
a	O
pedestal	O
,	O
which	O
also	O
acts	O
as	O
a	O
susceptor	O
.	O
</s>
<s>
Only	O
the	O
susceptor	O
is	O
heated	O
,	O
so	O
gases	O
do	O
not	O
react	O
before	O
they	O
reach	O
the	O
hot	O
wafer	B-Architecture
surface	O
.	O
</s>
<s>
The	O
reaction	O
chamber	O
walls	O
in	O
a	O
cold-wall	O
reactor	O
,	O
however	O
,	O
may	O
be	O
indirectly	O
heated	O
by	O
heat	O
radiating	O
from	O
the	O
hot	O
pedestal/susceptor	O
,	O
but	O
will	O
remain	O
cooler	O
than	O
the	O
pedestal/susceptor	O
and	O
the	O
substrate	B-Architecture
the	O
pedestal/susceptor	O
supports	O
.	O
</s>
<s>
This	O
may	O
be	O
necessary	O
for	O
some	O
gases	O
to	O
be	O
pre-cracked	O
before	O
reaching	O
the	O
wafer	B-Architecture
surface	O
to	O
allow	O
them	O
to	O
stick	O
to	O
the	O
wafer	B-Architecture
.	O
</s>
<s>
As	O
MOCVD	B-Algorithm
has	O
become	O
well-established	O
production	O
technology	O
,	O
there	O
are	O
equally	O
growing	O
concerns	O
associated	O
with	O
its	O
bearing	O
on	O
personnel	O
and	O
community	O
safety	O
,	O
environmental	O
impact	O
and	O
maximum	O
quantities	O
of	O
hazardous	O
materials	O
(	O
such	O
as	O
gases	O
and	O
metalorganics	O
)	O
permissible	O
in	O
the	O
device	O
fabrication	O
operations	O
.	O
</s>
<s>
The	O
safety	O
as	O
well	O
as	O
responsible	O
environmental	O
care	O
have	O
become	O
major	O
factors	O
of	O
paramount	O
importance	O
in	O
the	O
MOCVD-based	O
crystal	O
growth	O
of	O
compound	O
semiconductors	O
.	O
</s>
