Growth and properties of GaSb, Ga1-xInxSb and Ga1-xAlxSb epilayers by MOCVD

0146-3535/90 $0.00 + .50 @ 1990 Pergamon Press plc

Prog. Ctysta/ Growth and Charact. 1990, Vol. 20. pp. 285-312 Printed in Great Britain. All rights reserved

GROWTH Gal_Jn,Sb

AND PROPERTIES OF GaSb, AND Ga,_,Al,Sb EPILAYERS BY MOCVD

Fuh Shyang Juang and Yun Kuin Su Department

of Electrical

Engineering, National Cheng Taiwan, R.O.C.

Kung University,

Tainan,

ABSTRACT

compound

GaSb-based

low-noise diodes

avalanche

vapor

of GaSb,

deposition

GaInSb

ratio,

electrical

and AlGaSb growth

quality,

distribution

and

growth

epitaxial

organic

and the properties the effects growth

and

surface

properties,

laser

the metal

including

pressure

for

wavelength

conditions

layers,

temperature,

optical

long

we review

In this paper, (MOCVD)

materials

are suitable

photo-diodes(APD's)

and photodetectors.

chemical

III/V

semiconductors

rate

morphology

of on

and solid

coefficients.

I. Introduction Gallium-antimonide-based GaSb the wide 41.

substrates direct

wavelength GaSb and

bandgap

spectral There

are of

substrates low

have

range

So,

candidate

for

received

of their from

increasing

alloys

1.24um

two GaSb-based

is between

the

region

attention

corresponds

(AlGaAsSb) alloys:

(11 to

system

1.24 and 1.72~~1 which for optical

AlGaAsSb/GaSb

applications

fiber

system

in 285

long

lattice-matched recently

to

because

to wavelengths

AlGaAsSb

alloy

the AlxGal_xAsySbl_y

dispersion

fibers[S].

semiconductors

compound

over

a

4.3um(InGaAsSb)[2InGaAsSb.

The

lattice-matched

to

and

covers

communication

is a promising wavelength

low-loss

the in

silica

alternative lasers

and

286

F. S. Juang

photodetectors fluoride

glass

region,

l-2 orders

silica

fibers

fibers.

composition

of

matched

GaSb

cover

to

spectral

is

ratio[5]. factor

a

higher

It

is

in effect

a well

energy

very

composition

x.

equal

holes

hole

the excess the

splitting

Epitaxial

layers

(GaSb[12-161,

noise

Since

with MOCVD

impact

only

been or

is a very

ionization

for alloy

of the order

of the

impact

ionization bandill].

making

the

APD

MBE(GaSb[22],

This

the

approximately

(300K) where

liquid

can

ratio

B/a varying

is

to the bandgap

energy

phase

the

Eg[lll.

epitaxy

Gal_xInxSb[251,

in the literature

good method

(8

desirable

For example,

by

strongly

AlGaAsSb

20 for x=0.065

grown

noise

coefficients

valence

low.

>lum,

avalanche

In the

large,

rate,

a few reports

quantum

germanium

low

is extremely

of a AlxGal_xSb

usually

quantum

region and

ionization

split-off

equal

high

of an APD depends

gain.

would

high

to the

the resonant

and exceeds

lattice-

as an optical

the

the excess

is very

very

A is nearly

have

due

ratio

ionization

Gal_xAlxSb[17-211)

Gal_xAlxSb[23,24]) MOCVD.

the

8/a ratio

to 2 for x=O.28[5]

spin-orbit

by

from

in an enhanced and

that

at high

so that

(APD)

efficiency

8/a ratio

splitting

Eg[9-111, by

high,

fact

A large

spin orbit

initiated

noise

the

in the 1.3-1.6um

in the spectral

low quantum

and hole

operation

avalanche-noise

band-gap

attractive

in

wavelength

communication photodiode

of the best

grown

speed,

compound-APDs,

the signal-to-noise

(Y , respectively)[8].

the

For high

loss

wavelength

choice

system,

The emission

fiber

III-V

known

of electron

system,

alloy

multiplication

and

results

a suitable

have a very

the ratio

be

with

In

on

low

be reached

them more

APDs

in the 2-4um

that at 1.55um

1.7 to 4.3umf3.6.71.

low

Extremely

than

the use of an avalanche

makes

have

losses

substrates(y/x%0.9).

desired.

silicon

APDs

can

system.

lower

and low loss optical

efficiency where

of magnitude

from

range,

receiver

minimum

the InxGal_xAsySbl_y

the range

efficiency,

may have

This

and Y. K. Su

the InGaAsP/InP

besides

for growing

of growth

stable

solid

GaSb,GaAlSband GalnSb by MOCVD solutions

in

the miscibility

characterization

gap,

of GaSb-based

we review

compound

II. GaSb In 1979, Manasevit of producing

established.

MOCVD

growth

Then

in 1987

measured

characteristics

,

Schirar

growth

temperature, rate

inlet etc,

electrical

were

quality

photoluminescence material

by

MOCVD

they

with

photoluminescent crystalline

for the first

concentration

layers

time,

by Kaneko

They

not

data on

the

1982[27].

ratio

with

surface Hall

growth

pressure,

and total

mobility) window

GaSb

for

first

multi-quantum

well

mismatch[32].

quantum on GaSb

and

the

energy-gap

grown

gas

morphology,

also demonstrated

for GaAs/GaSb

more

In 1988, rate,

and

data

reflectivity

from a 7% lattice

been

have

in

III/V

and

well

strained

have

on InAs

the MOCVD

quantum

the

extensive

growth

correlated

strain

transitions

as

GaAs and InAs

conditions

by MOCVD[29].

of the cell,

et a1[30-311.

studied

growth

on infrared

grown

to establish

high

and

the feasibility

on sapphire,

epilayers

such

GaAs/GaSb/GaAs

heterostructures

single

layers

carefully

data

to determine

et al published

et al reported

(carrier

Haywood

grown

1989,

decided

of GaSb

geometry

growth

Growth

epilayers

parameters,

MOCVD

materials.

the optimum

Cooper

on GaSb epitaxial

detailed

flow

but

by MOCVD[26],

been

first

GaSb binary-compound

substrates yet

and Hess

287

the

In

structures

and

wells[47].

GaSb

substrates

by MOMBE.

et al in 1989[49].

Experiments It

was demonstrated,

trimethyl(TF-) be

used

source sources

and triethyl(TE-)

for preparing

mainly

by Manasevit

because

usually

used

GaSb.

et al in 1979[26],

metalorganic

They

preferred

of its low vapor for GaSb

growth

Ga and Sb sources to employ

pressure. were

TMGa

Since

the

that both

could

TEGa as the then,

Ga

the alkyl

and TMSb[27-321.

TMSb

.

TG ('C)

-9, 25- 50

'C, seem

0, 25-50

0, 75 -150

'C, seem

TMSb

InAs

(111)s

(100) (111)

0.6- 18,

GaA8 GaSb (0001) Al,O,

(100)2' InAs*

(111)A GaAs GtIAs (100) (0001) Al,O,

GaAs

(111)B

Substrate

2.16, 0.036

umlhr,Ew/min.

Growth rate

0.5 -2

1-3

Jff/V

Table

1: The growth

plane

conditions

* 2" toward (110) from the (100)

of GaSb

epilayers.

(100)2'GaSb:Te* l- 5, GaAs:Si 0.8-1.5 o-017-0.083 GaAs:Cr i550-650'~)

16

*c, seem

TEGa

llaywood 580-650 L30-321

12

7.5

(SLM)

TMGa

O.Ol- 0.3

530-640

total H, flow

C7.91

Schirar

coOper[271 500 -600

1261

Manascvit 475 -625

Ref.

GaSb Growth

P

8x 10"

3x 10“

t-l.5 x10"

3 x 10Lb

(cm-')

% P rc Ic

k 2

n v,

p 670-1000 (300K) 4850(7710

2600(77K)

610(300K;

Y? (cm'/v.e.;

GaSb, GaAlSb and GalnSb by MOCVD

is the primary The

source

temperatures

carrier

A1203

of alkyl

gas[26,29-321

GaSb

wafers

substrates

for

stabilized

under

reached. by

GaSb

stopping

the

growth

When

treatments

to remove

at

under

growth

end,

flowing

until

technique at high

The

proved

I.

susceptor

adequate

temperature The

precipitating

lower Sb

a high

film

and

growth

surface.

in protecting

on the InAs were

as were was

substrates

introduced were

into heat

used,

were

substrates

respectively.

At

the

the TMSb or AsH3 was

left

had

This

reached

the epitaxy

The and

GaSb

the

a

data

to its low

poor

250°C.

from decomposition

involving from

conditions

Good

quality

slight

III

This

pressure. but

profile

enough

and

listed

in

the

chance

of

To

this

offset

this led to nonuniform across

the

26 is indicative

substrate

of

SLM

was

poor

cell

for comment.

are

different

limited

single-crystal

gas phase

is in contrast

as

a total H2 flow rate of 27.5

are considerably

range[27,28].

rich

needed,

reference

alloys

3](27,28].

was

475-650°C,

the greater

vapor

temperature

arsenic-contailing

Group

was

temperature,

is not definite

growth

examined

flow rate

A compromise

used[26].

The

cooling,

used

temperature

and GaSb

TMSb

temperature

range

due

possibility,

design,

was

under

to GaSb)

substrates

substrates

on GaAs

I.

temperature[30].

growth

Table

films

of

in Table

been

growth

and TMSb

GaSb

and at 600°C

the reactor

the

TMGa

or

the oxide

AsH3

when

GaAs

the

rates

mismatch

InAs

out directly

flow before

flow

have

growth.

flow until

was carried

the AsH3

reactor[27].

800°C

arsine

InAs(O.B%

orientation

epitaxial

undoped

typical

SbH3[28,41].

are all listed

to GaSb),

different

289

to hydride

and

the bubblers

mismatch

with

an

is preferred

sources[26,32]

through

GaAs(7%

sapphire,

and

of Sb which

layers

(TMGa/TMSb

with

most

to

a

from much

were

ratio

As-containing

those

of

narrower

grown

between alloys

from 1

a and

which

290

F.S.JuangandY.K.Su

are grown

from a Group

the

more

much

contrast

which

complete

to

negligible

the

TMSb.

The

as

321 as shown to

the

arsenic

not be fully

in Table

very

arriving

and total H2 flows[30].

Most

epilayers

[271.

were

The TMGa

grown with

and TMSb

partial

and growth

in

and

Sb

Any

elements

into

have

grown

the

cracking

close

in GaAs)

of (see

to 1:1[30-

is probably

antimony

at the growth

altering

ratio

to

temperatures

was very

of elemental

due

for TMSb

the simple

at lower

seen

The

the alkyl

than

ratio

incorporated[31].

III/V

temperature.

cracked

effect(not

that any antimony

and both Ga

complex

mobility

expected

be incorporated

The III/V

I. This

low surface

so

must

is more

work[41,42]).

pyrolysis

growth

at the

situation

This may be in part

pyrolysis[33]

on the wafer

this will

Stringfellow's

AsH3

pressure

are deposited

gas stream.

low-temperature

slow

vapor

layer[27].

V rich

due

compared

surface

to

will

be

rate can be adjusted

gas phase

mole

fractions

pressures

were

2-6~10~~

of and

by

X1X10 1-3x10

-5

-5

,

respectively[29].

Haywood 8cm

et al even designed

diameter

outer

a variety

silicon

cell

of liner

to promote

inserts

laminar

in a horizontal

flow and

reactant

gas mixing[31].

Results Good

surface

morphology

range[28].

of factors,

were

seen

range

limits[27].

mole

fraction

surface (III/V

was obtained

at 650°C[31].

end of this a number

morphology

Optimum

on the wafers

was ratio

morphology

But surface not just

between

deteriorates

is too high

usually

obtained

<1)[31].

The

with

Droplets

ratio

and

outside

rapidly

antimony

of GaSb

films

on

needles the

1-3

if the total

rich on

poor

dependent

(>lxlO-4)[27,28].

a slightly

morphology

falls

with

at the higher

is critical

the temperature.

morphology

of TMGa+TMSb

is obtained

morphology

if the TMGa/TMSb

Surface

550 and 600°C

The gas (100)

best phase GaAs

291

GaSb.GaAlSband GalnSbby MOCVD TMGdTMSb 2 I

I I

RATIO 3 I

. .

_I

0 Figure

1:

IO

Growth

like

a crystal

(111) GaSb

substrate,

the

and

size

growth

dependent

agrees

reduced Haywood

the number

typical

with

with

with

a single

layer

orientation.

(100)

is generally

of the hillocks

when

concentration

the

growth

ts

1.0

the poorer

rate of GaSb

depend

that

on

On

like a mirror the

but

experimental

et al

growth 55OOC

for

in the

the growth

same

the

growth

rate

The growth in

TMGa

rate

Fig.2[27].

from 2.3 and

um/hr TMSb

rate may be a result

temperature[31].

was constant

is solely

concentration.

as shown

rate decreased

of TMSb at lower

temperature

that

in Fig.1[27].

decreased,

The reduction

rate of GaSb

and not on the TMSb

as shown

the at

the growth

by Cooper

ratio

um/hr

cracking

versus

data

temperature

et al reported

650°C

results[311,

TMGa/TMSb

concentrations[31]. of

mosaic

the surface

on the TMGa

increased

at

70

parameters[29].

From Haywood's

This

60

so

40

FLOW RATE &cm> rate of GaSb on InAs versus TMGa/TMSb ratio (from et a1[27] and that of GaSb on GaAs versus [TMGa] and

Cooper [TMSb]

appeared

30

20

for T>600°C

The

growth

and thermally

F.S.JuangandY.K.Su

292

0.10 THGa

HOLE

FRACTION

=

S.28XlgS

TtlSb

MOLE

FRACTION

=

2.64Xlt’

0.08

_

.s

G 5

0.06

k! T iz 0.04 pr 3 2 cl 0.02

0.00

520

500

540

560

580

600

620

640

GROWTH TEMPERATURE ("C> Figure

activated

for T>600°C

with

an activation

Ga species

were

controlling

Kcal/mole. growth GaAs

between growth 2: Relationship temperature for MOCVD-grown (from Cooper et a1[27]).

rate

of GaSb

also

as shown

in Fig.3.

It seems

that

III/V

ratio

good

surface

dependent optimum

slightly

on

from

mobility At

growth

the growth

to optimize above

the III/V

ratio

quality(u

was achieved growth

reported

1:l (different

P

1.2 to 1.7[30].

lower

is about

half

Haywood

at growth

that on (100)

by Haywood

et a1[311,

and PL spectrum from that required

in Fig.4[30].

=997 cm'/V.s,

300K)

the optimum

is

appeared

a

to obtain critically

to be

for for

that the highest

greater III/V

required

The window

et al reported pressure

The

The reactor

The hole mobility

as shown

pressure,

kinetics(371.

conditions[29].

rate,

III/V
and substrate on InAs

AEl of 41-42

the growth

the hole mobility

morphology:

electrical

TMGa/TMSb

[31].

affects

energy

on (111) GaSb

for the same experimental

pressure

peak

layers

rate GaSb

than

ratio

1000 needed

mbar to

GaSb, GaAlSb and GalnSb by MOCVD

293

6 TOTAL

FLOW

= 16 slm

TMGa FLOW = 30 seem

A A A A

A

A

0

I

300

I

600

Figure

Figure

4.

3. Growth rate et a1[311).

of GaSb

._ _ _

_

QOO PRESSURE

versus

I

I

I

-_

._a-

l5UO

I200

(mbar) cell pressure

The Hall mobility at 7i'K as a function ratio (from Haywood et a1[301)

(from Haywood

of III-V

reactant

F.S.JuangandY.K.Su

294

obtain

good electrical

[31]. The growth all reactor A

very

layers also

rate

also

pressures

grown above

the lowest

grown

temperature

550°C[31].

the

gas

total

variation on

flow

of mobility substrates

GaAs

those

TEM

IR

than

the

GaAs

above

at 77K<[303. Haywood concentration

and

The

drastically 12

GaSb

Haywood

SLM[31].

al.

cm'/V.s

These

uH=4850

values

The grown

Typically, at

et al reported as

when

epilayers

et

5000

substrate

about

a further

cm'/V.s

and

are comparable

to

material[34].

interface

of the

are present large

in the first

number

in the mobility

initial

growth

micrm

of

of

dislocations

were

when

the epilayers

were

lum thick[30].

as-grown plasma

spectra

by

is

77K) and

lowest

to

for bulk

in the mobility

growth[30].

reflectivity

MOCVD

studied

for the decrease

responsible less

a peak

also

that dislocations

heterojunction

the

temperature

of the GaSb/GaAs:Cr

confirm

at

with

was

temperature

77K) were measured

16 SLM

from

epitaxial

for

(4494cmL/V.s,

cmm3,

substrates

for good MBE-grown

micrographs

region

mobility

at 77. respectively[48].

obtained

growth

reduced

mobility

-3

found

rate

up 4300 cm'/V.s

cm

was

rate for

high mobility[31].

deteriorates

50K, with

pH=8x1015

A low growth with

that

(8.9x1015

be increased(xl.5)

The hole mobility

showed

in

The highest

on GaAs

material

increase

material

indicates

concentration

must

the mobility.

better

This

important.

sample

the

affects

in the hole mobility

600°C.

carrier

(high mobility)

produced

rapid decrease

extremely

for

quality

and optical GaSb

films

transmission

to determine

resonance

method

by Schirar

of epitaxial

p-GaSb

layers

substrates

concentration[29]. reflectivity

were

obtained Their

the carrier

as a non-destructive

confirms means

Typical

on n+-GaSb

used

were

reflective

the

usefulness

of characterizing

on

using

and also on

to calculate the

made

concentration

et a1[29].

grown

and were

work

measurements

S-1.

carrier of

IR

the carrier

GaSb,GaAlSband GalnSbby MOCVD density

295

of epitaxial layers grown on more conducting substrates where From Haywood's best sample

Hall effect measurement is impossible[29]. (GaSb/GaSb:Te),

the

the

photoluminescence spectrum was dominated by

narrow bound-exciton emission band (796meV), which has a half-width of 1.1 meV[30], LPE

grown

as compared with the best reported value of 0.3 meV

for

materials[34].

The

materials[35] and 2 meV for MB&grown

acceptor band (777meV) was much weaker, as shown in Fig.5. This is the only

reported

PL spectrum for MOCVD grown GaSb.

Observation of

same dominant acceptor peak (777meV) in the PL spectra from grown

the

materials

by all the various techniques points to the same native

defect

being responsible for the electrical properties[30]. The nature of the native

defect in GaSb is residual acceptor which is connected with an

Sb-vacancy.

Other

the

probable models were suggested for

defect;

consisted of a Ga atom on the Sb sublattice (Ga antisite,

they

or a complex of a Ga-vacancy (VGa) with GaSb[12,44-461.

I. 1

I

0.75

The

GaSb)

ultimate

I

I

0.77 ENERGY

a7q

0.81

(eV>

Figure 5. The PL spectrum of GaSb/GaSb:Te Haywood et al(301).

recorded at 4K (from

F. S. Juang and Y. K. Su

296 limits

for mobility

defects

The

existing

showed

a poor

results

do

slightly

III/V

and Haywood[32]

highly

strained

time

was

interface in

a

with

sample

microcrystallites grown

exceed

The

15 i

1000-25000

PL

could

mobility) best

The

electrical

PL

data,

to be achieved

at

a

in the best

(SQWs)

islands

about

be

resulted

in

a

set

30 300;

GaSb

thick

but again

growth

to relax thickness

15 i

the for

strained

dislocations,

MQW

the individual

GaSb

island such as

area

with

structures

were

time,

was observed.

a

layer

The

GaSb.

growth

on

time did not yield

of elastically-relaxed of misfit

The

The GaSb

limiting

the growth

of the

deposited

no dislocations

the

by a network

with

been

accommodation.

with

growth

mismatch).

lattice

of GaSb have

elastic

to

but

the QW and MQW

an

layer

did

not

[32J.

properties

cm'/V.s

from

be due

(10K)

of GaSb/GaAs

of GaAs).

The

single

the 1.27 eV peak

(below

the effect

the GaAs

of the strain

to a transition,

QW structures 3-5x1015

at 77K and n-type:

all showed

spectra

arising

band.

best

appears

system(7%

Increasing

layer

characteristics

GaSb/GaAs

high

than that resulting

a 15 A layer

successfully

electrical

the

completely

is accompanied

SQW

also

wells

QW growth.

strained

interspersed

quality

the

investigated

15 f; appeared

heterostructure thicker

quantum

with

(i.e.

acceptor

with

(0.88-1.23)

also

5 set giving

strain[32].

optical

GaAs/GaSb/GaAs

single

by MOCVD

to the native

(1.23-1.48)[30].

Chidley

GaAs

may be due

results

a strong

correlate

ratio

material

electrical

with

exactly highest

lower

strained

good

PL spectrum

The

electrical

gave

not

therefore.

concentration

in GaSb materials.

which

sample

and carrier

were

cmT3(all

and multi

dominated

by

QW structures

of

in photoconductivity

band

gap of 1.52

on the GaSb

indirect

in real

mobility:

and

which

was

gap[321.

This

from the

GaAs

eV)

energy

space,

(77K)

297

GaSb, GaAlSb and GalnSb by MOCVD

conduction

band

to

the GaSb valence band(calculated to

be

%0.75eV

[47] 1, as a result of electron tunnelling into the thin GaSb barriers. Alternatively,

the

1.3eV peak might represent the GaSb indirect

transition,

Xc-+ rv(mj=3/2][321.

(0.75eV)

this transition (Xc-+I',,,] for a GaSb/GaAs well

of

coincide

with

combination into

observed

the

However,

energy(l.3eV)

in

PL

of an error in the band offsets and/or

does

not Some

spectra.

incorporation

As

GaSb could account for the significant change of

the

energy

calculated

the

gap

the

band

structure[47].

III. Ga l_xAlxSb Growth Cooper et al first reported the growth of Gal_xAlxSb and Al 1-xGaxAsySbl-y on InAs substrates by MOCVD from TMAl, TMGa, TMSb and AsH3

in

1980[36].

distribution

In 1983,

coefficients

Stringfellow

studied

the

solid-vapor

in Ga l_xAlxSb alloys grown by MOCVD using a

kinetic mode1[38]. In 1986, Bougnot et a1[37] achieved MOCVD epitaxial growth

of

mirrorlike

Gal_xAlxSb surface

(0 x 0.5)

morphology

on

GaSb

and good

substrates composition

with

nearly

control

appropriate growth temperature and vapor phase compositions.

using

In 1988,

Chidley et al found that both the crystallinity and electrical quality of

MOCVD grown Gal_x Al x Sb were limited by carbon

contamination

from

the TMAl starting material[32]. Experiments The

GaSb/Ga l_xAlxSb system has

attractive for epitaxial growth. electrical

0.65% mismatch making it However,

potentially

both the crystallinity and

quality of MOCVD grown Gal_xAlxSb were found to be limited

by carbon contamination from the TMAl starting material[32] and by the oxidation

of aluminum.

The substrates were Sn-doped

(100)2O

toward

600

640-680

600

Bougnot (37)

Haywood (321

('C)

T6

Cooper C363

Ref. flow

2 -3.5

(SLM)

H,

tot.41

Ca,_xA1,Sb

'C

.

TEGa

Table

-9: 15-30 (Sam)

toward

2’ partial

toward

2’

5-37 (BCUII)

from

(001)

(100)

(P.P)

4.2x10-+

Group

conditions

pressure

toll)

(110)

-2O’, 1-2x10-‘ (P.P)

from

x 1o-e

(P.P.1

2.2

'C

TMSb

2: The growth

p.p.:

(b)

(a)

18’)

0=,0.5-~b40.~~-‘o.5a10-4 (P.P.) (P.P)

*C

TMGa

Growth

1-2

< 1

VI ICI

(a)

0.1,

0.2,

o
O.l
x

0.5

Ga ,_x AlxSb

ePilaYerS

(b)

GaAs

GaSb

InAs

(001)2’GaAs

(lll)B

(100)

(100)2”

Substrate

of Gal_xAlxSb

plane

plane

III

i

growth

-3pm

0.07-0.11

0.035

(umlmin)

rate

P

5xld’-ld (77K)

(cm-')

pP

2;; (77K) 43

(cm'/v.s)

7

?

;

t Fi

v,

GaSb,GaAlSband GalnSbby MOCVD InAs[ll],

(110)

Te-doped

n-type

(100)

and

insulating

(100)

GaAs wafers[37],

as listed

substrates

were

maintained

an arsine

decomposition of

while

600°C(36].

growth

A

value

partial

TMSb partial

of the GaSb

pressures

greater

is heated

pressure

temperature

the

It

is

than one

the wafers[36].

was

The growth

II. to

Typical

group

InAs

prevent

temperature

at

4oo"c

semi-

The

to the growth

about

formation

or

atmosphere

its

final prevent

to

III and

TMSb

and 2.2x10W4,

to maintain

conditions

GaSb

in Table

of 4.2~10~~

necessary

to prevent

(111)B

was maintained

substrate[l2].

are of the order

respectively[36]. ratio

the susceptor

when

decomposition

under

299

a

III/V

of droplets

reported

vapor-phase

and needles

are listed

on

in Table

II

for comparison.

Results From

(002)

dark

tetrahedral

field

defects

aluminum

containing

analysis

showed

aluminum layers so

was

substrates, and

overcome

giving

a poor

cross-section

content

higher

a small to

be

e.g.

problem

symmetry

(111)

mosaic

level.

guide

to

probably

(C2H5)3A1[32].

density(371.

a

all

with

on

orientation Gal_xAlxSb well

(100) are grown

oriented

morphology[37].

of an undoped

than

contamination

a two-fold

surface

in

of the as-grown

to be a poor

on

the

spectrometer(SIMS)

the surface

materials,

symmetry

in

content(%lO l8 cms3)

appears

with

interface,

density

this contamination

starting

seems

cases

mass

the high carbon

therefore,

three-fold with

at a high

ion

carbon

In many

hillocks

substrates

crystallites

AlSb

a

observed

GaAs

A cleaved

To

visible

Secondary

flat despite

the use of other

orientation

on

and

of a GaSb/Ga0.SA10.2Sb

to be a high

layers.

quality.

GaSb

typically

there

morphology,

surface

requires

On

shiny

clearly

are

layer.

containing

material

TEM micrograph

10 at.%

p-type

Gal_xA1,Sb

on an n+-GaSb

epilayer

substrate

with

was observed

300 by

F.S.Juangand Y.K.Su SEM after

rate

chemical

of the order

changes

little

revelation

of 0.035

over

of the p-n

um/min

the range

junction[37].

was observed[36].

of alloy

A

growth rate

The growth

compositions

investigated

(x:0-

0.65)[36].

The

composition

the

input

variation

V/III the

fluxes

ratio

data

composition

temperature

2 (data from

Cooper

et

Gal_xAlxSb

generally

and more

substitution

reported

occurs

elements

in the

range

et a1[37]).

both

From

found

to be

on ternary

on the

by

(Ga,Al)

adjusting [36].

of the partial

of O-O.8

is shown

group

Also

shown

Fig.6,

in Fig.6

the

approximately

III-V

solid

0.0

Figure

0.2

0.4

Al/Ga+Al

PARTIAL

6. Mole fraction function of et a1[36]

GaAs

III(non-volatile)

substrate

(from

0.6 PRESSURE

of AlSb

0.8

sublattice

Bougnot

et al )

Bougnot

et al >

1.2

RATIO

in Ga

Al Sb epilayers as a (from Cooper Xv=PTMA1'PTMA:"TM~a

and Bougnot

et a1[37]).

on

where

et al )

1.0

are

unity

solutions

Cooper

on

in

distribution

by Stringfellow[41].

o

The

PTMSb'2x10-4 atm and a constant

a1[36].

are

regulated

x s as a function

680°C,

from Bougnot

coefficients(xs/xv)

the

III

xV=PTMA1/PTMA1+PTMGa

at a growth ratio

can be easily

for the column

of the Al solid

pressure Fig.6,

of the crystal

GaSb, GaAlSb and GalnSb by MOCVD

Assume

that

reaction

TMGa

in the vapor

Ga and Al reach range

and TMAl

of

the growing

growth

distribution

phase

the

coefficients

substrate

range

640-680°C.

shown

in Fig.7,

et

a1[37].

thermally deduced mole

They

Solid but The

was

1371.

are controlled composition

explained

with

and growth

that

growth

does

rate

and

on the

xv in

the

composition,

as

Bougnot

kinetic

considerations

by

the Al flux

at the growth

surface

a thermal

activation

energy

from the relationship temperatures

of the

by

nature

AE2

between Gal_xAlxSb

which AlSb

7: Mole fraction qf AlSb in Gal_xAlxSb epilayers function of 10 /T (from Bougnot et a1[37]).

is was

solid

epilayers

I _

Figure

III

group

as reported

at constant

of solid

then

In the normal

not depend

dependent

homogeneous

interface,

by diffusion

dependence

with

the growth

by diffusion[41].

both

temperature

be 43 Kcal/mole

fractions

interface

301

by

decomposed

reaching

is temperature

assume

controlled to

before

temperature,

Stringfellow[41,42]. of

are completely

as a

F. S. Juang and Y. K. Su

302

IV. Gal_xInxSb

1986,

Bougnot

Gal_xInxSb

grown

on GaSb

grown

on

GaSb

substrates

morphology

but

In

lattice

et at first presented

a

growth

substrates

First

were

coefficient

were

dislocations that

a

energy

15Sb/GaSb

effects

MQW

quality et al

with

surface

increasing

studied

of layers

grown

The variations

of the optical

x and spectral

were

shown[38].

of GaSb/Gal_,In,Sb, grown

with

et a1[32,481. hole

structures,

et al reported

the InGaSb

molecular

epitaxy(MOMBE)[49].

present

observed

in

the

on GaSb

absorption of

single

mismatch

interfaces

a and for few

and

et al reported wells

of

from the measurements

of

one

oscillations[48]. for

growth,

~1.2%

In 1989, Haywood

gas was

Haas

abrupt

on

response

In 1988,

with

solid

the

on the composition

for different

of

layers

good

and

and Shubnikov-de

beam

The epitaxial

a rather

on the growth

results

temperature

successfully by Chidley

experimental

exhibit

Bougnot

heterojunction

two-dimensional

Gag . 851no Hall

(x50.5)

wells

quantum

x50.5

crystalline

obtained[38].

versus

MOCVD

substrates[371.

1988,

results

Ga0.611n0.39 Sb/GaSb

x=0.2,

with

In

dependence

rate.

multiple

and GaAs

decreasing

mismatch[37].

composition

Growth

the first

of

Kaneko

In 1989,

time, by metalorganic

Experiments The

growth

growth have

conditions

were

been deposited

Wells)

similar

listed

P'QW

The

of 300;

to those

in Table

by MOCVD[37,381

of Gag . E,Ino 2 Sb/GaSb

a1[321. layer

procedures'were

sample

have

III.

of Gal_xA1xSb Bulk

layers

and 2D structures

been

successfully

had a buffer

layer

[36].

of Gal_xInxSb

(Multi

grown

The

Quantum

by Chidley

of 2um GaSb

and

et

capping

GaSb[32,48].

Results Gal_xInxSb

(15-50%)

Gal_xAl,Sb[32].

proved

The surface

considerably morphologies

easier

to

of Gal_xInxSb

grow

than

epitaxial

layers

303

GaSb, GaAlSb and GalnSb by MOCVD

4

3 d

4

N

P

rn C H

b

x

304

F. S. Juang and Y. K. Su

grown

on

GaAs

Gal_xAlxSb

and GaSb

substrates

epilayers[37].

On

were

all similar

(100) GaSb

substrates

epilayers

show a mirrorlike

surface

typically

for x>O.45

where

mismatch

exceeds

glossy

but

density

granular[37,38].

is higher

epilayers poor

seem

Surface

than on (100)

as expected

features

also

For III/V=5, when

the growth

probably

due

to the fact

content,

Ga-In-Sb

vapor

the

phase

phase

In

III/V=lO/S

and substrate

cross-sections

observed

by SEM after

Unstable

growth

temperature

of Ga l_xInxSb chemical

was observed

due to the TEIn

is greater

is deposited

with

is

hillock

substrates, giving

and on the

III/V

of droplets

and

were

This

than 575OC.

alloy,

of

is

indium

high

from

as predicted

Bougnot

et

al,

on

ranging

525 to 600°C[38].

from

epilayers,

on GaSb

substrates

of the growth

at high TEIn pressures

by the

few defects

epilayers

a

mismatch[37].

on the substrate

ternary

revelation

condensation

the

crystallites

temperature

the experiment

condition,

the surface

On GaAs

lattice

the

few hillocks;

substrates,

at low temperature

solution

diagram[38]. growth

>0.3)

that,

,

and the appearance

than the solid

preferred

Cleaved

damage

temperature

liquid

rather

on growth

x20.45,

very

-2

3x10

oriented

the huge

for

with

substrates[38].

from

surface

(111) GaSb

with well

depend

observed

the

On

to be a mosaic

morphology

ratio.

the lattice

to those of

were

were

junction[37].

(PTEIn/PTEIn+PTMGa

or decomposition

into the gas

line

[371.

The

dependence

of In solid

xv=PTEIn/PTEIn+FTMGa

for ~~50.3

(550-70OOC)

was

X

xv c 'urves move

S

versus

temperature,

Bougnot

as

itudied

shown

et al rcaorted

composition

and for different

by Bougnot away

xs on vapor

et a1[37].

phase

growth

composition temperatures

It is observed

from the x,/x,=1

line with

that the

increasing

in Fig.8[37].

that

solid

composition

x increases

rapldly

with

MOLE FRACTION P .O b I

*E:

of InSb in the SOLID

\

\

\

4*

\

l

\ \ \

\

. .

\

\

\ \4 \

y,

\

. \

\

\

\

\

\

MOLE FRACTION

\

-\

\

t*

\/

\ \

\

\

\

of InSb in the SOLID

H

F. S. Juang and Y. K. Su

306 decreasing mainly and

growth

because

600°C

range[37,38]. in Table

For

InSb growth

rate rate

growth

the growth

the

growth

at

Fig-lo.

This for

seems

rate

as

shown

is thermally

in

Fig.9[38],

activated

to be constant

values

for GaInSb

rate

increases

a constant

growth

rapidly

temperature

result

experimental

between

layers

530 same

the

in

are shown

parameters

introduced

to take account

vapor

or effective

This value

could

Bi

sticking

indicate

with

slowly

whereas

increasing

InSb

550°C[37,38],

can be fitted

where

phase

varies

rate of Gal_xInxSb

8,,/5,,=3,

presence

575OC

III.

content

curve

growth

Typical

x10.2,

x,0.2,

the GaSb

where

under

temperature

coefficients

with

are

phase

and/or

as shown a

of the gaseous

the GaSb

in

is enhanced

by the

substrate[38].

“c

d

P,,,=/0&?7

i

0

P

/

MOLE FRACTION of InSb in the SOLID Figure

the

species.

I-

T= 500

in

theoretical

reactions

that the Ga incorporation

of In in the vapor

solid

phenomenological

of chemical

coefficients

for

10. Growth rate of Gal-x InxSb versus solid composition at constant growth temperature (from Bougnot et a1[37]).

GaSb,GaAlSband GalnSbby MOCVD GaSb

On

substrates layers

Gal_xIr~xSb

grown

under

alloys reported Chidley

by

there

decrease

buffer

improvement layer

relationships

Gal_xInxSb

and

compositions bandgap

the

the incoming

of Gal_xInxSb

in mobility

when

were

optical

photo-energy measured

can be deduced

ternary content,

observed

on GaAs and

GaSb

pure

InSb

were

grown

indium

in the Gal_xInxSb/GaAs

between

(x=0-0.14)

results

a

growth

significant

an AlSb

There

or

by MBE[43].

absorption

coefficient

for layers

with

different

et a1[38].

The energy

by Bougnot

from the absorption

edges.

I.1

I.0 GalnSb

I 0

I

0.05 MOLE

Figure

1

I

I

0.1

0.15

0.2

FRACTION

by

substrates

contentE32.481.

using

the

between

in the

increasing

epilayers

increasing

with

density

in hole concentration

with

densities

Compared

with

for Gal_x In,Sb

from 0 to 0.4%,

carrier

Similar

et a1[38].

was an increase

with

the carrier

slightly

307

x ranging

temperature.

conditions,

Bougnot

a substantial

p-type

at room

in hole mobility

All_xInxSb

The

to

et a1[32,48]

decrease was

cme3

the same

seems

for composition

are always

and 6~10~~

2x1016

that

and

0.25

of InSb in the SOLID

11. Energy bandgap variation versus mole fraction in GaInSb layers (from Bougnot et a1[38]).

of InSb

of

The

308

F. S. Juang and Y. K. Su

bandgap

variation

Fig.11.

There

deduced

from

versus

composition

is a good

agreement

x is also presented, with

the theoretical

Sb/GaSb

Ga0.611n0.39

the range

0.47-0.64,

Given

the lattice

least

the first

dislocations for

micron

Chidley

[32,48]. showed

and

a

in 1988.

no dislocations

which

diagram[48]. observation cm'/V.s,

of quantum

gas

In

InGaSb

substrates

single

by MOMBE

appear

emanating

effect

high before

from

using

TEGa,

TMIn

ratio

of

InGaSb

from

with

at 1.5K

crystalline

the

is

in the

11

cm

about

wells

of

by Haywood

and

abrupt

this sample

both

well,

the

the

calculated in

( a Hall mobility -2

of

heterojunctions

oscillations

of 1.2x10

the onset

growth

grown

at

dislocation

to be flat with

to carriers

in one of the Gal_xInxSb

composition

TMIn/TEGa

7Oi) was also

due

in

to GaAs,

four Gao_81no.2Sb

Haas(SdH)

Hall

a

heterostructure

in good agreement

concen,tration

of 2D hole

have

and photoconductivity

Shubnikov-de

a hole

1989,

was

compound

thickness

The wells

signa1(0.717-0.729eV) of

will

critical

50,

(1)

a low photoresponse

GaInSb

A MQW with

40,

Photoluminescence

position

solid

predicted

layer[32].

et a1[32,48]

interfaces

as

et al in 1988[38].

of the ternary

of the epilayer

thickness(20,

shows

by Bougnot

in the Ga l_,In,Sb/GaSb

a single

different

reported

The

[401

p-n heterojunction

mismatch

density[30,32].

70;

variation

in

Eq.(l).

Eg=0.172+0.139(1-x)+0.41S(l-x)2 *

as shown

) indicate

p

xx of

band and 2100

the formation

wells[32,48].

layers

have

and solid is

been grown

antimony[49].

linearly

on

GaSb

The

In/Ga

dependent

on

the

flux[49].

V. Conclusions

A

detailed

Gal_xInxSb

review and

of the MOCVD

Gal_xAlxSb

growth

epilayers

and characterizations

of

has

including

been

reported,

GaSb,

GaSb, GaAlSb and GalnSb by MOCVD

experimental pressure

procedures and the effects of III/V

and growth rate on hole

morphology compound

and growth

As-containing quality 3. The

solid

mobility,

distribution

PL

309 ratio,

temperature,

properties,

coefficients.

The

surface

GaSb-related

conditions are considerably different from those

alloys and are limited in a much narrower

range.

Good and

epilayers can be grown with III/V ratio just between 0.5

The work to grow doped GaSb-based materials is still in growth

of AlGaSb were limited by carbon contamination

TMAl

source.

than

Ga l_xAlxSb.

Gal_xInxSb

Gal_xInxSb(15-50%)

alloy

of

progress. from

proved considerably easier to

the grow

The bandgap variation versus composition x in has been studied.

The quantum well

structures

‘of

GaSb/GaAs and Ga l_,In,Sb/GaAs have been successfully grown by MOCVD.

ACKNOWLEDGEMENT The authors wish to express their thanks to N.Y.

Li and K.J.

Gan for

very useful discussions and suggestions. This project was supported by the National Science Council,

Republic of China,

under the

contract

NSC79-0417-E006-04.

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F.S.JuangandY.K.Su

Yan-Kuin Su was born in Kaohsiung, Taiwan on Aug. 23, 1948. He received the 0. S. degree and Ph.D. degree in electrical engineering fran National Cheng Kung University, Taiwan in 1971 and 1977, respectively. Ran

1977 to 1983, he was with the Department of Electrical Engineering,

National Cheng Kung University, Taiwan as an Associate Professor, and was engaged in research on ccmpound semiconductors and optoelectronic materials. In 1983, he was promoted to Professor of Electrical Engineering. Rran 1979 to 1980 and 1986 to 1987 he-was on-leave and working at University of Southern California and AT&T Bell Laboratories as a visiting 'scholar,respectively. He has published over 100 papers in the area of thin film materials and devices and optoelectronic devices *His current interests include canpound semiconductors, integrated optics and microwave devices. Dr. Su is a member of IEEE, a member of Chinese Society of Engineering, and a n-emberof Phi-Tau-Phi.

Fuh Shyang Juang was born in 1964. He received the B.S. 1986 and the M.S. degree in from the National Cheng Kung is a Ph.D. candidate now and semiconductors.

Taiwan, Taiwan, R.O.C. on July 30, degree in Electrical engineering in electrical engineering in 1988, both University, Tainan, Taiwan, R-0-C. He major in III-V compound l