Electrophysical properties of p- and n-type InSe intercalated with Li and Ba

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Electrophysical properties of p- and n-type InSe intercalated with Li and Ba

V. Kulbachinskii, M. Kovalyuk, M. Pyrlya

To cite this version:

V. Kulbachinskii, M. Kovalyuk, M. Pyrlya. Electrophysical properties of p- and n-type InSe intercalated with Li and Ba. Journal de Physique I, EDP Sciences, 1994, 4 (6), pp.975-979.

�10.1051/jp1:1994116�. �jpa-00246958�

Classification

Physics

Abslracts 71.25T

Electrophysical properties of _p- and n-type ^Inse intercalated with Li and Ba

V. A.

Kulbachinskii,

M. Z.

Kovalyuk

and M. N.

Pyrlya

Low

Temperature Physics

Department, Physics Faculty, Moscow State Lomonosov

University,

119899, Moscow, Russia

(Received 7 Decelnber 1993,

accepled

Il Februaiy 1994)

Abstract. p-polytype of Inse surgie crystals of p- and n-type are intercalated with Ba and Li by electrochemical process. This

compound

shows to be _a

good

host for the insertion of Ba _or Li

atoms at room temperature. ^The temperature dependence of the resistivity in the temperature

range 4.2<T<300K and the magnetoresistance ^{at T=4.2K} are

investigated.

Electrical transport measurements on Ba _or Li intercalated n-Inse and

p-Inse

show _a decrease for n-Inse and

an increase for

p-Inse

of the

resistivity

with respect to non-intercalated

samples.

Weak localization

was observed in the host n-Inse samples.

Introduction.

Indium selenide

crystals belong

to the A'~~B~~

family

of

layer

semiconductors. Inse

crystallizes

into stacked

hexagonal layers

each

consisting

of four

close-packed

_monoatomic sheets in the sequence Se-In-In-Se. Inse _is characterized

by

_strong covalent bonds inside the

layer

and it has the

predominantly

van der Waals nature of

interlayer

bonds. The existence of _van der Waals

gaps allows _{one to} insert guest atoms between

layers.

Ba _or Li intercalated indium selenide may be

applied

as solid solution electrodes, in

particular

in those _cases where intercalation _is

possible

_{over a} wide

stoichiometry

range. For this _reason Inse _{is a}

good

candidate _as intercalation electrodes. Its

photoconductive

behaviour and

photomemory

effect

[1, 2]

_permit the

design

of _a dual device _a

secondary battery,

combined with _a

photovoltaic

system.

Weak

interlayer

bonds facilitate the existence of several

polytypes conesponding

to a

different

stacking

_sequence of the

layers.

^The

simplest

and most described

polytypes

ⁱⁿ the

family

A~~~B~~ _{are e,}

p

and _y. The influence of Li intercalation _on the emission spectrum ^of Inse _was

investigated

in references

[3, 4].

Here _we report on the influence of the intercalation with Ba and Li _on the temperature

dependence

of the

resistivity (4.2

~ T

~ 300

K)

and _on the

magnetoresistance at T

=

4.2 K

(B

~ 7

T)

^{of the}

p-Inse

_p- and n-type.

976 JOURNAL DE PHYSIQUE ^I N° 6

Samples

and

experimental technique.

Single crystals

of

p-Inse (with

the space symmetry group

D(~)

_{were grown}

by

the

Bridgman

method.

Samples

with dimensions 4 _{x x} 0.5 _{mm were cut} from _an mgot

by

_a diamant _saw.

The intercalation _was

performed by

_an electrochemical process. This method

gives

the

possibility

to obtain

crystals

intercalated with _a concentration of metallic _atoms up ^to

10~'

_{cm~ ~. The Inse electrode was mounted} in _a way ^to expose the

layers perpendicular

to the c-axis, to the

electrolyte.

The cell _{was at} direct _cunent which _never exceeded 10 ~LA. The

number of intercalated _{atoms was} calculated from the

charge

^{which flowed}

through

the

samples.

To obtain uniform

samples

we used _a small _cunent and _a

long

^{time of}

exposition

of the

sample

in a solution.

Electrical contacts to the

samples

_were made

by

In

evaporation

_or silver

paint.

Both types ^of

contacts appear ^to have ohmic behaviour at the current range

10~~-10-6A. During

the

measurements the current was directed in basai

plane along

the

c~-axis

and the magnetic ^field

was

applied perpendicular

to the _cunent and _to the

layers.

A

magnetic

field up to 7 T _was

produced

with the

help

of _a

superconducting

^solenoid.

The host

samples

of Inse

(n-type semiconductor)

had _{a room}

temperature resistivity

value of p w 20 Ohm. _cm

(first type)

or p 1300 Ohm. cm

(second type).

For the

synthesis

of p-type

Inse _we

doped

^{Inse with 0.1at%} Zn

[5, 6].

The _room temperature

resistivity

of the

p-Inse samples equals

_p

1 3 000 Ohm. _cm.

Results.

In

figure

_we show the temperature

dependences

of the resistance of

(1)

_a host n-Inse

sample

of the first type

(room

temperature

resistivity

_{p 1} ^{20 Ohm.}

cm),

the _same

sample

intercalated

with Ba up to a concentration of about

10'~

_cm~ ^~

₍₂

_and

10~°

_cm~ ^~

(3

). In

figure

2 _we present

the temperature

dependence

of the _resistance of _a host n-Inse

sample

of the second type

(room

temperature

resistivity

_p

w 300 Ohm.

cm) (1),

the _same

sample

intercalated with Ba up ^to a

concentration of Ba _atoms of about

10~° cm~~ ₍₂

_{and the}

same

type

^of

sample

intercalated

with Li with the _same concentration

(3).

In the temperature range 100~T~ 300K _we

observed an activation behaviour of the resistance with the activation energy

E~w

190 mev for the second type ^{of the}

samples (an

activation behaviour _is shown _m

Fig.

2

by straight fine).

The electrical

properties

of the host materials _are modified due _to Ba _or Li intercalation. Ba _or Li intercalation enhances the n-character of the

samples. Resistivity

_is thus decreased in

Ba,Inse

_or

Li,Inse

m the whole temperature range. For low temperatures ^Ba or Li intercalated n-Inse shows _a

change by

several orders of

magnitude

of the

resistivity

with respect to non mtercalated

samples.

The value of activation energy decreases from

-

190 mev to -170 mev for the

high

resistance

samples.

For the first time _we also

mvestigated

the influence of Ba _or Li intercalation _on the electrical properties ^of

p-Inse.

In

figure

3 _we show the temperature

dependence

of the resistance for host

p-Inse (curve

1), Ba

(2)

and Li

(3)

intercalated

samples.

A

comparative study

of n-Inse and p- InSe

samples

shows that Ba _or Li intercalation enhances the n-character of the

samples.

For _p- type

Li,Inse

_or

Ba,Inse,

resistivity ^increases as x

increases,

due to the hole compensation as Li

or Ba enters the lattice.

The

positive

transverse magnetoresistance ^{observed in Inse for} temperatures ^T~50K decreased _{as a} result of

coohng,

and then became

negative

_m low

magnetic

field rismg m the absolute _{sense as a} result of

cooling

to 4.2 K. After the initial

negative

magnetoresistance a

further _{mcrease m} the magnetic ^{field created} a

positive

effect

(Fig. 4,

_curve

1).

The negative magnetoresistance ^{has the}

followmg

features _: 1) it

depends quadratically

on the magnetic ^field

m weak fields up ^{to B} - 0.01Tesla

2) lowering

of T reduces the range of the

quadratic

log(R,koml

loglRkom)

<

2

3

3

3

0 10 o 10 ^~'

Fig.

l.

Fig.

2,

Fig. l.

Dependence

^{of the} resistance

(logarithmic

scale) _on the reciprocal of temperature _: 1) n-Inse

2) ^n-Inse

(10'~ Ba)

3) n-Inse

(10~° Ba).

Fig. 2. Dependence of the resistance (loganthmic scale) _on the reciprocal of temperature : 1) ^n-Inse _; 2) n-Inse

(10~°Ba)

_; 3) n-Inse

(10~°Li).

dependence

_;

3) beginning

from B

1 0.03 Tesla the

resistivity depended logarithmically

_on the magnetic ^field.

Figure

5 shows the relative

change

_m the _resistance of n-Inse at T=

4.2 K

plotted

_as a function of the square

(a)

and of the

logarithm (b)

of the magnetic ^{field. After} the intercalation the magnetoresistance ^becomes

positive.

The relative

change

_in the _resistance

AR/Ro

_{was very} small for the intercalated

samples (curve

2,

Fig. 4).

In intercalated

samples

the anisotropy ^of

conductivity

becomes less than _in host

crystals.

Discussion.

The characteristic features of the magnetoresistance ^observed at T

~ 10 K in the host n-Inse

samples

are m fuit agreement ^{with the}

theory

of quantum corrections to the

conductivity

m the two-dimensional _case

[7-9], according

to which the

magnetoresistance

should be

quadratic

_m

weak fields and

logarithmic

_in strong ^{fields. The}

quadratic dependence

_range should

expand

on

the increase of the temperature, as observed

experimentally.

^{The results obtamed indicate that}

at low temperatures ^the

conductivity

of _our

crystals

_was

govemed by

the two-dimensional electrons which exhibited weak

localization,

because of the capture ^{of electrons}

by

two-

dimensional defects _in the basai

plane, typical

of A~~~B~~

layer crystals [10].

In

n-type

^Inse at

978 JOURNAL DE PHYSIQUE I N° 6

7)

^log(R,Moml

3

2

'~

o Q5

Fig. ^3.

Dependence

of the resistance

(logarithmic

scale) _on the

reciprocal

of temperature : 1)

p-Inse

2) p-Inse

(10~' Ba)

3)

p-Inse (10~' Li).

~#

,?o

Bi

(mT)~

B mT

°

40 80 120 20 _100~

éo

$

~ce o

ce

.~~

~ _OE

<

2 _.

20 B,Tesla (a) (b)

Fig.4.

Fig.5.

Fig.

4.-Dependence

of the relative change in the resistance AR/Ro of magnetic ^field B at T 4.2 K _: 1) n-Inse, 2) n-Inse

il

0~°

Ba).

Ro is the resistance at B

= 0.

Fig.

5. Relative

change AR/Ro

in the resistance of n-Inse

sample

at T 4.2 K

plotted

_{as a} function of the square (a) and the

logarithm

(b) of the magnetic ^field.

T ~ 2 K clear Shubnikov-de Haas oscillations _were observed due to two-dimensional electrons present ^with a

density

of 2 _x 10~ ^~'

cm~~ _{[11 ].}

Ba _or Li intercalation results _{m an increase} of the free electron concentration m n-Inse and the weak localization regime

disappears.

In

Li,Inse

or

Ba,Inse samples

we may observe

only

weak

positive

magnetoresistance

(see Fig. 4),

which is _a

typical

for disordered metallic systems.

Li,Inse

and

Ba,Inse samples

_possess 3D

conductivity

at low temperatures. ^{Thus after} the mtercalation process the conduction is due to bulk process.

For

p-Inse samples

we observed _an activation behaviour of the

conductivity (see Fig. 3).

For p-type

Li~Inse

_or

Ba,Inse

the

resistivity

_{mcreases as x mcreases} due _to the hole compensation

as Li _or Ba _enters the lattice.

At _room temperature ^the

change

_in

conductivity

due to intercalation _{is not so}

high

as

expected

from the concentration of the intercalated _atoms. It _means that

charge

^transfer from mtercalated _atoms to Inse matrix _{is net} very effective _at this

temperature.

^The same result was

obtained

by optical

method for

y-Inse

intercalated with Li

[4].

In conclusion we may

emphasize

that the electrochemical _{reaction was} reversible. Thus Li and Ba intercalated Inse may be used in solid _state ionic devices. The

change

of _carrier

concentration _{is a} result of the Fermi level

displacement

_owmg to the

change

transfer from the mtercalate. The _same result _was obtained for

Bi~Te~

mtercalated with Li _or Ba

[12].

References

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Phys.

Selnicond. 22 (1988) 720).

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Paraskevopoulos

K. M.,

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