Electric field effects on intersubband transitions in quantum well structures

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,

Rev.

Lett.

J.S.

Weiner, T.C. A.C.

(1985).

J.

Phys.

Schultheis, and

C

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D.S.

W. 1148

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Gaillard,

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G.

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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.

Phys.

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Mendez,

Phys.

Phys.

(1986).

localiza-

given

J.A.

Jpn.

island-

of

approximately

10.

broa-

in to

(1984).

Erman, tran-

simple;

due

Burrus,

2173

(1985).

intersubband is

also

under

va-

differen-

fluctuations

L

tlonz3is

clear

C.A.

Chemla,

field-dependent

argument to

well-width

a

and 53,

App.

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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D.A.B. Damen,

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This

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dening

4.

energy

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

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Harris,

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