Supertattices
and fl/licrostructures,
ELECTRIC
FIELD
EFFECTS
ON
QUANTUM K. Department
of
F.-Y.
Juang,
Bajema
and
Hong,
The
report
on
electrons The
theoretical peak
MI
resonances,
the
field.
is
the
to
been
properties
part
by
which
are
based
by
in
very
broadening
co+cl
is
to
of
heavy-hole
by
the
Stark
in
GaAs-AlxGa
tical
techniques.
In
on
Raman
this
exciton Experieffect I
_
x
has A
9,9,10
(RS)
[co(cl)
derived good
from
field and latter sh,>wn
in
due a
to
nearly
in
by
Al0 with
SGaQ 7As, thickness
Al0
3Ga0.7As
;;$.3Gao.
,
by
field-enhanced
lowest
Raman
co+cl
intensity
in
peak
with
inversion
field-independent
exciton
shifts
differs
from
resonancea,f?hi3iting broadening.
pumped
by
powers
layer
are
inferred
shows
the
the
electrode.
corded
in
symmetry,
normal The
[llO]
to and Figure
for V
ext.
a
is
a the
the
1) The
and
1
these
values of
coated
(~70%)
sample on
spectra
and
and
were
and
the off
re-
z(x',y')i where
x',
y'
z
are
is
along
directions. shows
RS
external peak
at
the
determination
configurations [liO]
ra-
density
QWS
intensity
layers
laser in
power
z(x',x');
the
at dye
range
the
Raman
different The
the
150Raman
200um
P:6-lOWcm-2; from
a
performed
laser. spot
in
scattering
backscattering
behavior
Art
between
of
and
an
estimated
interface
build
(pyridin
to
A
was
sample.
were
were The
to
the
LDS698
focused
applied width. the
a
reflectivity very
of
measurements CW
indicaundoped.
contact Au
top
scattering
clad
unless
nominally
T=2K
wells
0.19um
and
layer;
evaporating
using
GaAs
(198-A-thick
are
on
a
the
:;;~;pe;*Ig_um
Schottky
film
on
in
uncoupled
barriers),
by
experiments epitaxy
substrate
L=264A
5 ayers
was
our
;;;;;;
clad
defects
difference.
beam
thirty
As the
this
in
GaAs
semitransparent
the
associated are
used
structural
molecular
(001)
O.l-0.15w.
co+cl
Stark
account
sample
grown
dious;
theoretical
broken
finding
of struc-
for
laser,
ehotoexcited
measurements
The
increase
of
to
beam
a of
the
state band].
with
calculations.
exci-
independent
originated
shown
absorp-
of
of
denotes
our
agreement
parity-
by
is
on
investigation
well
conduction
have
report
dependence
(first-excited) the
Stark
infrared we
transitions
electrons
an
far
electric-field
intersubband
with
addition,
work,
scattering
the
to
;;;;:;;nsc;cs;e;;;; the
transitions
using
In
intersub-
due
effects
The
device
absorption,
intersubband
udied
the
Disorder
was
field.
excitonic
use
of
strucagreement
shown
nearly
formed (PL)
of field
A-thick shifts
photoexcited
good
intensity applied
of
optical
induced the
electric-field of
Si-doped
in
investigated
QWS's
of
the
attention.
shifts
resonances
are
attributed
(yWTgs;,ia;;_
motivated
mentally,
is
the
quantum-well
enhanced of
effect
~~~~~~~~:~;~,s~~s.,,high-speed pronounced
of
transitions
The
width
feature
of
electronic
much
terest
the
structures
attracted
June 1987)
with
the
Science,
Michigan,
A10.SGa0.7As
rapidly
Bhattacharya
Computer
48109-2122
shifts
to
P.K.
and
study
predictions.
perpendicular
the
GaAs-
Stark
This
studies
fields on
A
Michigan,
disorder.
Recently,
quantum-well
264
contrast
ton
29
of
and
of
scattering
increases In
Singh,
intersubband
measured
band
tural
layers
a
with mixing.
Raman co+cl
in
ture.
electric
a
of
48109-1120
University
(Received
dependence
MI
Arbor,
IN
Merlin
Engineering
Ann
We
R.
University
J.
Electrical
TRANSITIONS
STRUCTURES
The
Arbor,
S.-C. of
INTERSUBBAND
WELL
Physics, Ann
Department
685
Vol. 3, No. 6, 1987
at
18.9meV
data
of
d.c.
voltages (V,,t=O)
Q1987Academic
the
QWS is
Press
due
Limited
686
Superlattices
Cl
-3v
CO
and Microstructures,
Vol. 3, No. 6, 1987
2
E
c
2
J-L ;\
- 2K /A-oilZ(X',Y')Z
10
.1.5v
15
20
lL f v)
G t
u”
2'5
ELECTRIC FIELD (kVcm-1)
RAMAN SHIFT (meV) Fig.
1:
Raman spectra of the 264-A GaAs-AlO 3GaOezAs QWS show ng the on at intersub and transit co+c1 different external voltage S . The laser energy is w,=1.685eV Counting rates at-t!? maxima are typically - 400 c 5 W-l. The inset shows a schematic energy diagram (not to scale].
intersubband transitions of A calculation using the bandontinuities determined by Miller predicts c +c -18.4meV. In the 's inv!?st!gated range of V -3VSVextS0. ea3 , the FWHM (full-width at half maximum) of co+clremained nearly at r3meV. With increasing the intersubband peak growths in and shifts to higher energies, except for 05Vext"0.2V. Since the shift and intensity 'must be even functions of the electric field, it follows that -0.2V is the built-in voltage of the structure. The observation of the co+cI transition indicates that the lowest subband in occupied. This is the sample is partial1 I1 due to photoexcitation , as revealed by results on the P-dependence of the scattering (not shown). A crude estimate based on parameters from the literature7
to
elec
c
+c1
0rons.
Fig.
2:
Comparison between measured (full circles) and calculated cC+cI Stark shifts.
gives a ste dytate elect$on concentration 0-2x10 a cm -' (P=lOWcm). (I can also be determined from the positions of the intersubband peak in th (x1,x') and $2 The bare tran(x',y' ) configurations. sition energy is given by the latter, while (xl, x') exhibits a shift proporo o due to depolarization efOur data reveal no appreciable shifts (
tering mixing
states
have
different parithat the scatenhancement results from paritydue to the field as in field-inbsorption by forbidden exci-
-dependence of the shift of The 'ext is shown in Fig. 2, together with CO'C resu f ts of calculations. Theory and experiment are in very good agreement if a
Superlattices
and Microstructures,
length
2.7um
of
tages
into
the
is
the
were
of
due
to
our
case. width
of
of
differs ted8,12,13
significantly
our
of
a
exciton
is
in
by
most
cases
at
nishingly
high
fields;
small
In
defects
tiation
of
The due
roughness
and
and
9.
Struc-
conditions
the
average
11.
Kash,
E.E.
Horikoshi,
Y.
=w-6L
12.
by
of
E
,
the
the
15
field
corre$ponding
ercitc,ns'I>I, for
give
using and
kVcm_I). other
E.J.
Austin
and
6L
to
work
Lightwave
was
Science
as
impurity
Polland,
Kuhl,
E.O.
15.
L.
55,
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J.S.
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C
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14.
while
T=O.jmeV
do$g
mechanism:
1 0 8 0 .3
(one
and
L1091
Ploog:
For E
parameters
monolayers,'
tering]
energy
transitions.
the
(E=O)
Since 3-4
the
with
6L=2.838
T=G.4meV
ceed
increases
intersubband
Calculations strilcture
is
excitation.
r
decreases
Q
173
(1986).
(II
and
H.
46,
Fischer,
Rev.
Bhattacharya,
13. where
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A.
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Mendez,
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(1986).
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given
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island-
of
approximately
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broa-
in to
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Erman, tran-
simple;
due
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2173
(1985).
intersubband is
also
under
va-
differen-
fluctuations
L
tlonz3is
clear
C.A.
Chemla,
field-dependent
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a
and 53,
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T.C.
Wiegmann,
Lett.
Appl.
are
W.
Wood,
Wood,
structure).
to
the
excitons
sItions.
they
our
lead
between
8.
rela ivel 2-&,7-la,Y?%0;;dnt
studled
very
is
ro ghness 1Y (tun-
fluctuations
are
7.
which
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T.H.
l8, broa-
interface
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6.
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the
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(1985).
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D.A.B. Damen,
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a
This
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effects
dening
4.
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negligible
from
determined
ridthe.
used
to
the
nearly
cO+cI
reslllts.
inter-well
tural
11
to
field--induced
neling
We
Ref.
are
of
feature
cept
in
observaton
dependent
mainly
electron
corrections which
3.
5.
The
ar'd
quasibound numerically.
tunneling,
dening
vol-
687
calculations,
described
imaginary
convert
the
obtained
procedure
avoid
to
In
ergenenergies
states
in
used
fields.
Vol. 3, No. 6, 1987
J.S. 50,
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