<s>
The	O
heterojunction	B-Algorithm
bipolar	I-Algorithm
transistor	I-Algorithm
(	O
HBT	O
)	O
is	O
a	O
type	O
of	O
bipolar	O
junction	O
transistor	O
(	O
BJT	O
)	O
which	O
uses	O
differing	O
semiconductor	O
materials	O
for	O
the	O
emitter	O
and	O
base	O
regions	O
,	O
creating	O
a	O
heterojunction	O
.	O
</s>
<s>
Detailed	O
theory	O
of	O
heterojunction	B-Algorithm
bipolar	I-Algorithm
transistor	I-Algorithm
was	O
developed	O
by	O
Herbert	O
Kroemer	O
in	O
1957	O
.	O
</s>
<s>
Due	O
to	O
the	O
need	O
to	O
manufacture	O
HBT	O
devices	O
with	O
extremely	O
high-doped	O
thin	O
base	O
layers	O
,	O
molecular	B-Algorithm
beam	I-Algorithm
epitaxy	I-Algorithm
is	O
principally	O
employed	O
.	O
</s>
<s>
In	O
addition	O
to	O
base	O
,	O
emitter	O
and	O
collector	O
layers	O
,	O
highly	O
doped	O
layers	O
are	O
deposited	O
on	O
either	O
side	O
of	O
collector	O
and	O
emitter	O
to	O
facilitate	O
an	O
ohmic	O
contact	O
,	O
which	O
are	O
placed	O
on	O
the	O
contact	O
layers	O
after	O
exposure	O
by	O
photolithography	B-Algorithm
and	O
etching	O
.	O
</s>
<s>
IBM	O
and	O
others	O
use	O
ultra-high	O
vacuum	O
chemical	O
vapor	O
deposition	O
(	O
UHVCVD	O
)	O
for	O
SiGe	O
;	O
other	O
techniques	O
used	O
include	O
MOVPE	B-Algorithm
for	O
III-V	O
systems	O
.	O
</s>
<s>
A	O
pseudomorphic	B-Algorithm
heterojunction	I-Algorithm
bipolar	I-Algorithm
transistor	I-Algorithm
developed	O
at	O
the	O
University	O
of	O
Illinois	O
at	O
Urbana-Champaign	O
,	O
built	O
from	O
indium	O
phosphide	O
and	O
indium	O
gallium	O
arsenide	O
and	O
designed	O
with	O
compositionally	O
graded	O
collector	O
,	O
base	O
and	O
emitter	O
,	O
was	O
demonstrated	O
to	O
cut	O
off	O
at	O
a	O
speed	O
of	O
710GHz	O
.	O
</s>
