Monday, November 6, 2017 11:30 am
-
12:20 pm
EST (GMT -05:00)
The Waterloo Institute for Nanotechnology (WIN) presents a seminar by Dr. Philip Klipstein, from the Antimonide Based Compound Semiconductor Research Program (ABCS), Semiconductor Devices (SCD), Haifa, Israel
InAs/GaSb/AlSb Superlattice Detectors and Topological Superlattices
Abstract
As
first
predicted
by
Sai-Halasz,
Tsu
and
Esaki
in
1977,
type
II
superlattices
(T2SLs)
based
on
alternating
layers
of
InAs
and
GaSb
exhibit
rather
unique
properties,
including
a
zero
bandgap
at
a
critical
value
of
the
layer
thicknesses.
In
this
respect,
T2SLs
bear
a
close
relationship
to
the
alloy,
HgxCd1-xTe
(“MCT”),
where
the
bandgap
vanishes
at
a
critical
value
of
the
composition
parameter,
x.
MCT
photodiodes
are
widely
used
as
tunable
infrared
detector
elements,
because
they
offer
a
versatile
technology
that
can
match
the
characteristic
photon
wavelength
of
most
infrared
applications.
On
the
other
hand,
InAs/GaSb
photodiodes
have
suffered,
historically,
from
higher
dark
currents
and
fabrication
issues
that
have
severely
limited
their
uptake
in
similar
applications.This
position
has
changed
recently,
due
to
the
development
of
a
new
XBp
barrier
architecture
and
a
new
and
robust
passivation
process.
A
640
x
512
format,
15
μm
pitch
LWIR
focal
plane
array
detector
was
demonstrated
in
2016
by
SCD,
with
a
quantum
efficiency
of
>50%,
a
pixel
operability
of
>99%,
and
a
dark
current
only
about
one
order
of
magnitude
larger
than
the
state
of
the
art
Rule
07
value.
The
SCD
T2SL
XBp
detector
contains
both
an
InAs/GaSb
active
layer
(AL)
and
an
InAs/AlSb
barrier
layer.
The
physical
principles
of
the
detector
will
be
described,
together
with
simulation
methods
that
can
predict
the
detector
quantum
efficiency
and
dark
current
from
a
basic
definition
of
the
superlattice
period,
the
AL
stack
thickness
and
the
minority
carrier
lifetime.
For
layer
thicknesses
greater
than
the
zero
bandgap
values,
both
InAs/GaSb/AlSb
and
HgTe/CdTe
superlattices
undergo
a
transition
to
a
topological
insulator
phase
(TI).
Some
basic
properties
of
the
topological
phase
will
be
discussed,
including
a
graphene
like
dispersion
at
the
TI
transition
and
possible
advantages
of
the
TI
phase
for
low
temperature
spintronic
devices.
Between
1976
and
1982
Philip
Klipstein
received
his
B.A.and
Ph.D.
in
Physics
from
Oxford
and
Cambridge
Universities
respectively.
After
two
years
as
a
Junior
Research
Fellow
at
Cambridge,
he
moved
to
a
tenured
post
at
Imperial
College,
London.
Research
included
transport
and
optics
in
GaAs/AlAs
and
Si/Ge.
In
1990,
he
returned
to
Oxford,
adding
research
into
antimonide
heterostructures,
and
was
promoted
to
Reader
in
2000.
Following
a
sabbatical
at
the
Weizmann
Institute,
Israel,
in
1998,
he
joined
Semiconductor
Devices
(SCD)
in
2001,
where
he
is
currently
principal
investigator
of
the
Antimonide
Based
Compound
Semiconductor
research
program
(ABCS).
He
is
author
to
more
than
140
publications
including
5
patents.