journal of applied physics cuprous photovoltaic cells

8/10/2019 Journal of Applied Physics Cuprous photovoltaic Cells

1/7

Cuprous oxide indium tin oxide thin film photoYoltaic cells

Masaharu Fujinaka

Department

of

Electronics Tokyo

Denki

University Chiyoda-Ku Tokyo 101 Japan

Alexander

A

Berezin

Department

of

Engineering Physics McMaster University Hamilton Ontario Canada L8S 4M1

(Received 25 June 1982; accepted for publication 14 January 1983)

We studied thin films of cuprous oxide deposited on glass coated with transparent conducting

ind ium-tin oxide (ITO) films. The deposition

of

both

Cu

2

0 and

ITO

was made by rf sputtering in

an Ar/02 gas mixture.

For

the deposition ofCu

2

0 a pure copper target was used and

ITO

films

were deposited from a disk target, the halves

of

which were made ofSn and In, respectively. This

allows variation of the stoichiometry of the deposited

ITO

film by changing the position of the

substrate glass beneath the Sn/ln target. X-ray diffraction

of

Cu

2

0 films indicates the typical

pattern

of

amorphous material. We were able to produce Cu

2

0 films

of

different stoichiometry by

varying the O

2

to Ar ratio during rf sputtering. The maximum resistivity of the films corresponds

to an ideal stoichiometry ofCu

2

0.

An

activation energy of 0.55 eV found from thermostimulated

conductivity is related to excess

Cu

vacancies. The band gap found from the spectral dependence

of the photovoltaic effect is 2.0 eV. The composition of

ITO

films was studied by Auger analysis

and can be described as a variable composition mixture ofSn0

2

+ x and

In

2

0

3

+

y To

produce an

Ohmic electrode, gold was evaporated on the top

of

the

Cu

2

0

film

and hence the resulting

structure

of

the photocell could be specified as

ITO-Cu

2

0-Au,

for which we propose a barrier

band diagram. We studied the photovoltaic characteristics of the fabricated photocells under an

incandescent lamp with 100mW/c m

2

output. The open-circuit voltage and short-circuit

current

of

our

cells were about 20-90 mV and 50 uA/cm2 respectively, and some dependence of

the outpu t characteristics on the composition ofITO film was observed. Conversion efficiency for

thin films Cu

2

0/ITO

cells was found to be substantially lower than for Cu

2

0/Cu Schottky

barrier cells. This is tentatively attributed to small diffusion lengths and/or presence of interface

recombination centers.

PACS numbers: 85.60.Dw, 72.40. + w, 73.40.Lq,

8U5.Cd

I INTRODUCTION

Cuprous oxide (Cu2

0

is

considered to be a useful mate

rial for photo voltaic energy conversion because it has a prop

er band gap ~ 2 . 0 eV), high efficiency

of

generation

of

pho

tocarriers and also because of its potential low cost. Cuprous

oxide thin films can be also produced

by the same sputtering

technique as indium-tin oxide (ITO) films considered ear

lier.

with an oil diffusion pump system. The water cooled target

was 12.7 cm in diameter and the distance between the upper

and the lower cathodes was 9.2 cm.

Most of the earlier studies

of Cu

2

0 photocells included

Schottky barrier, MIS, and heterojunction structures based

on thermally prepared CU20

or

electrodeposited Cu

2

0

see,

e.g., Refs.

2-9

and references therein).

t

is the purpose

of

this paper to report on the study of

the photocells

of

Cu

2

0 deposited on glass coated with trans

parent conducting

ITO

films

of

different compositions.

The

ITO

can form a heterojunction with

Cu

2

0 film

4

5

as well as

be used as a window material for solar radiation.

The deposition of both

Cu

2

0 and

ITO

was made by

radio-frequency

rf)

sputtering of metals in an Ar/02 gas

mixture. Some dependence of the output characteristics on

the composition of

ITO

film was observed.

II. EXPERIMENT

The schematic diagram

of

the apparatus used in this

work is shown in Fig. I. The basic sputtering system was a

Materials Research Corporation type

8551 rf

sputter unit

After pumping down to a background pressure of

6 X 10

Torr

in the sputtering chamber,

Ar

and O

2

gases,

controlled by separate flowmeters, were mixed together in

the gas mixture chamber, and then introduced into the sput

tering chamber through a gas leak valve. Then,

we

raised the

total pressure to the desired value of2.5 X 10

3

Torr

in order

to keep the discharge continuous and the plasma stable. The

target was sputter cleaned for a few minutes with a shutter

covering the substrates. Finally, the deposition was started

by moving the shutter.

III. ITO PREPARATION AND CHARACTERIZATION

The transparent conducting

ITO

films were deposited

by rfsput tering in the gas mixture of Ar flow rate: 100 cm

3

/

min) and O

2

flow rate: 20 cm

3

/min) on cleaned micro slide

glass (Sargent-Welch Scientific Company). The disk target

consisted of two semicircular parts which were made of Sn

and In, respectively 0.5

mm

thick, 99.99% purity). This im

purity level is probably not very important for the overall

resistivity of he film (it is basically dominated by the

In

to Sn

ratio), but it may be essential for the recombination processes

at the Cu

2

0/ITO interface. This finally can have a detrimen-

3582 J. Appl. Phys. 54 6), June 1983

0021-8979/83/063582-07 02.40

1983 American Institute of Physics

3582

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2/7

pow r

_ ..... ..:..:.. supply

tal effect of a conversion efficiency (see Sec. VI). The deposi

tion time was

18

min at an rf power level

of

50 W.

The position

A,B

F

of

the glass substrates and the

relative sizes

of

Sn

and In

are shown in Fig.

2.

Figure

2(a)

is

for the case when the disk target consists of two equal halves

ofSn

and

In, respectively. Figure

2(b)

is for the case when the

In side is substantially larger than the Sn side [see insert in

Fig. 2(b)]. We measured the electrical resistance, the Auger

signal, and the optical transmit tance to evaluate the compo

sition of the fabricated

ITO

films.

1

To measure sheet resistance

of

ITO films we used two

parallel evaporated gold electrodes

of

5-mm length with 0.3-

mm

gap between them (see the insert to Fig. 5 for the similar

arrangement). The measured sheet resistances are shown in

Fig. 2.

The resistance changes rapidly just beneath boundary

of

Sn and In on the target. By moving the position of sub

strate glasses toward In side, the resistance can be decreased.

The observation of the energy spectra

of

Auger elec

trons emitted from the

ITO

films provides an effective tool

M

FIG. I. Schematic diagram of the apparatus

for the deposition of thin

films by

the radio

frequency sputtering system.

FM

= flow

meters).

for the chemical analysis

of

the composition. The Auger

spectra

of

samples

A, C,

and

E of

Fig. 2 are shown in Fig. 3.

In the case of 50% Sn-50 In target [Fig. 2(a)], the main

spectrum (Sn

430

) of Sn at 430 eV was stronger than the main

spectrum (In

404

) ofIn at 404 eV. In the case of he target with

a larger indium side [Fig. 2(b)] the line In

404

was stronger

than Sn

430

in contrast with first target.

In

each case, the

atomic concentration

of

Sn and In in

ITO

films was deter

mined by measuring the peak-to-peak amplitude of the cor

responding element (Sn

430

or

In

404

)

with elemental sensitiv

ity factors,1O and was shown in Fig. 2. Due to the partial

overlap

of

Sn

430

and

In

404

lines the accuracy

of

determina

tion

of

concentrations is relatively low. An indirect indica

tion of this accuracy may be drawn from the position of

resistivity minimum in Fig.

2(b).

We think that this accuracy

is sufficient for the purpose of our semiqualitative analysis.

Our

Auger

data

relate this minimum with approximately

1:9

ratio ofSn to In. A similar minimum found in 11 corresponds

to 4-6 wt. %

of

Sn02 in Sn:In

2

0

3

mixture.

I t is obvious from Fig. 2 that the resistance correlates

with the relative concentration ofSn and In in the ITO film.

Position of Snlln target

I d ~ ~ ~ = T ~ l n C = = = ~ 1

d

___

.......... In

C o n ~ i - .

I ---.

I

I

I

I

I

I

I

Sn

I

80.-

60Q

~

a:

4 ffi

)

z

8

2

1

A

B

D E F

Ia)

lO'---..;..t.;....--,----.J:-L.:L-....:L......i..--..IO

Posit

on of subs tr

ate

glass

3583 J. Appl. Phys., Vol. 54, No.6, June 1983

4

1

:

~ l

z

~

(J)

ID

2

::1

I

~ c I

Sn

In

,0

5mm

I

102

mm

r

1 --

__

I d l ~ _ A ~ ~ B ~ _ C ~ S ~ n _ D ~ _ E ~ - ~ F ~ ~

Position

of substrate

glass

8

o b)

FIG.

2.

Room temperature sheet resis

tances of transparent conducting ITO

films

with respect to the configuration

of

Sn/In target and the position of substrate

glass. Electrodes length 5 mm, gap

between the two paralIel Au electrodes is

0.3

mm. (a) Symmetrical In/Sn target; (b)

nonsymmetrical In/Sn target. Insert to

Fig.

2(b):

The configuration of the non

symmetrical In/Sn target. 1-1-1: resis

tance;

. - . - . :

concentration.

M.

Fujinaka and

A. A.

Berezin

3583



3/7

A

C

: e.

1.0

C )

C )

1.0

C )

o t

:d

;d

:d

:d

:d

n

Sn

430

n

0

04

b)

n

404

The overall resistance

of

samples in Fig.

2 b)

are higher than

those in Fig.

2 a)

in spite

of

increasing the concentration

of

In. The deposition rate was changed by increasing the area

of

In target because In has a relatively lower sputtering rate. As

a result, under the same sputtering conditions (power, sput

tering time, and constant

flow

rate: Ar: 100 cm

3

/min; O

2

:

20

cm

3

/min), the thickness

of

ITO film

is smaller in the case

of

In>

Sn

target than for the case when 50 Sn-50

In

target

was used.

The relative concentration

of

oxygen in the ITO films

was constant regardless

of

the position of the substrate as

follows from almost constant Auger signal (0

52 0

,

about

50 ). As a result,

we

can describe our ITO films as a vari

able composition mixture

of Sn 0

2

+

x

and In203+y

lxi,

Iyl < ), where x and y reflect the excess

or

deficit

of

a lattice

3584

J. Appl. Phys. Vol. 54 No.6, June 1983

E

1.0

:0 :d

n

404

oxygen relatively to the ideal stoichiometry.

Sn 0

2

was a

dominant participant when the symmetrical

SnlIn

target

was used [Fig.

2 a)],

whereas In20 3dominated in ITO films

when the second, In-dominated target was used [Fig.

2 b)].

Then,

we

observed the spectral dependence

of

the opti

cal transmittance in the visible region which

is

shown in Fig.

4 a)

for the case

of

Fig.

2 a)

target. The case

of

Fig.

2 b)

target

is shown in Fig.

4 b).

The relative transmittance

of

In-richer

ITO films was

80 -90

and rather spectrally unsensitive

in the visible region. At the same time the transmittance of

Sn-richer areas could be substantially

imprOVed at

a shorter

wavelength by increasing In concentration. The samples

and in Fig.

4 a)

have spectral characteristics similar to

those shown in Fig.

4 b)

due to the increasing proportion

of

In

as could be seen in the Auger signal.

M. Fujinaka and

A. A.

Berezin

3584



4/7

100

80

---

~

~ 6 0

Z

~

t::

~ 4 0

C/)

Z

~

I-

20

F.

...... . . ...-

. : ; ; a ~

.......... ,.,. ............ ( : 4 ~

...-.

/E / %. .,.; ............

/ . ,eh./AI'

~

/ :.,

..... ..,

~ C

... ... .

.'_.,.

-..................

BC 0 E F

100

80

FIG. 4.

Optical transmittance for

ITO

films.

(a)

For

the target of Fig.

2(a);

(b)

for the tar

get of Fig. 2(b).

O ~ - - - - - - ~ - - - - - - ~ - - - - ~

O L - - - - - - - ~ - - - - - - ~ - - - - - ~

0.4

0.5

0.6 0.7

0.4

0.5

0.6 0.7

la)

WAVELENGTH ,u.

m)

WAVELENGTH C)L m

b)

IV. Cu

2

0 PREPARATION AND CHARACTERIZATION

We studied thin films of Cu

2

0 deposited by

rf

sputter

ing in constant

Ar

flow (flow rate 100

cm

3

/min and various

Oz flow rates (5, 10,20,30, and 50 cm

3

/min on glass. The Cu

target used for sputtering had 99.9 purity and was 3 mm in

thickness. All Cu

2

0

films for the electrical conductivity

measurements were made by supplying an

rf

power level of

150 W for 20 min, and the films obtained had a thickness of

the order

of

4500 A. Thickness

of

all CUzO films were mea

sured by a Taylor-Hobson (TALYSURF4) probe.

Gold electrodes were evaporated on top

of

CUzO films

as shown in Fig. 5. The electrical conductivity of the films

was measured at room temperature and the results are also

shown in Fig. 5.

The obtained CUzO films exhibited a minimum in con

ductivity (0 min - 10- 3 n 1 cm - 1) at an oxygen flow rate of

approximately 20 that of Ar (100 cm

3

/min . The film

which corresponds to this ratio of

flow

rates probably corre

sponds to an ideal stoichiometry of

CUzO. At

lower

Oz

per

centage than this minimum point, the conductivity of the

films increases because

of

the larger copper content than in

ideal CUzO. Higher levels

of

O

2

flow

result in an increase of

the conductivity presumably because of the admixture of

CuO to CUzO. We also measured the thermostimulated con

ductivity

of

films fabricated

at

various

Oz

flow

rates (10 ,

20 , 30 , and 50 of Ar flow rate) in the region from

-

50C

to + 85 C. The results are shown in Fig. 6. The

conductivity at a relative Oz flow rate

of

5% is not shown

because the obtained film behaves like metallic Cu. The acti

vation energy

of

the thermostimulated current

of

the films

corresponding to the oxygen flow rate of20% was calculated

from linear log I

vs

T - 1 plot (labeled in Fig. 6 as Ozo ), and

is equal to 0.55

eV

[assuming the conductivity -exp( - acti

vation energy/2kT)].

Based on these results we have chosen the Oz and

Ar

flow rates of20 cm

3

/min and 100 cm

3

/min, respectively, for

the subsequent fabrication of CUzO photocells.

3585

J.

Appl. Phys., Vol. 54, No.6, June 1983

V.

PROPERTIES OF ITO/Cu20 HETEROJUNCTION

CELLS

To produce an ohmic electrode for the cells, gold was

evaporated on the top of the CUzO films (20 Oz flow rate),

10

~ ~ ~ ~ i l l Z i I ~ r H + - - t h i n

film

5

10

-6

5X10

r ) I J I ,

o 10 20 30

40

50

02 to

Ar

( )

FIG.

5. Electric cur rent for the films ofCu

2

0 deposited for various O

2

to Ar

flow ratios,

at

rf power level 150 W for 20 min, at bias of 5 V.

M.

Fujinaka and A. A. Berezin

3585



5/7

200

250

T K)

300

350

400

FIG.

6. Electric

current

vs reciprocal te mperature for

Cu

2

0

films

of

Fig. 5.

0

, 020

0

, and

0'0

are 10, 20, 30, and

50 of 0

in the gas mixture,

respectively. Bias is 5

V.

which are deposited on glass coated with ITO films of differ

ent composition. Hence the resulting structure of the photo

cell could be specified as ITOICuzOI

Au as illustrated in the

insert to Fig. 8.

In the case when the sputtering power level was 150

W,

we could not obtain samples having a rectifying1-

V

charac

teristics, possibly because of the presence of many recombin

ation centers

at

the junction interface of ITOICuzO formed

due to the particle bombardment during the discharge.

However, by decreasing the sputtering power level, we could

observe the characteristics such as shown in Fig.

7.

The ITO

film used for the samples represented in Fig. 7 was a sub

strate of the type C from Fig.

2 a).

For

CUzO

films sputtered

at a power level of75 W rectification can be obtained for all

types of

composition

of

ITO films i.e., A-F from Fig.

2).

The 1- characteristics for the cells were measured un

der dark conditions and under illumination

of

about 100

mW

cm-

2

calibrated by light meter LI-I85A of LAMBDA

Instruments Corporation) with an incandescent lamp Syl-

vania Co.)

of

750 W placed 20 em from the face of the ITO

films. For the ITO films from Fig.

2 a),

we were able to find

the dependence of the photo-output on the composition of

ITO films, but we could not find such pronounced depen-

3586 J. AppL Phys., Vol.

54, No.6,

June

1983

FIG. 7.1 V

characteristics for the ITO/Cu,O/Au cells

at

different sputter

ing power levels. The substrate is the

ITO

film at the position C in Fig. 2 a).

rf

power level

W)

150

100

75

thickness A)

4500

2500

2000

sputter ing time min.)

20

25

30

dence when the ITO films from Fig. 2 b) were used. This

difference may be related with the overall high resistivity

of

ITO films from Fig. 2 b) to that from Fig.

2 a)

and with possi

ble differences in conduction mechanisms of In

z

0

3

:Sn and

Sn 0

2

:In films which are not yet fully understood. II

For the cells

of

the type A and F from Fig. 2 a), we did

not show their characteristics in Fig.

8,

because of the possi

ble influence

of

the end effects from the sputter ing Cu target

and also because of the decrease of the photo-output.

PhotovoItaic output was studied only for ITO films of

the composition with Sn > In and the maximum open circuit

voltage was obtained for the ratio of n : I n ~ 8 : 15.

For

the cells deposited on substrates

of

the types B, C,

D, and E, the spectral distribution of output open circuit

lighti>

+

Au 2.

5m

rt

cu

2

0

dia.)

ITO

substrate glass

-0.2 -0.1

60

0.2

V v)

FIG. 8. Dark

solid lines) and iIluminated dotted lines)

I V

characteristics

for the cells fabricated on

ITO

substrates of different composition in Fig.

2 a). rf power level used: 75

W;

sputtering time: 30 min; thickness

of

film:

2000

A

M. Fujinaka and

A.

A. Serezin

3586



6/7

1.0

w

rJ

z

0 0 5

Cl.

rJ)

w

a:

:I:

Cl.

.........

....... .........

/ .

/0 .

.

_.......

.

.......

. ,..

.

. - ........ .

.' E . . ~ ....

.

.

q,:4 0.5 0.6 .7

WAVELENGTH CJL m)

FIG. 9.

Spectral distributions for the cells (of Fig. 8) made from

ITO

films

of

Fig.2(a).

voltage was measured as the function

of

the wavelength as

shown in Fig. 9. The maximum photovoltaic peaks were es

sentially similar to those found for

Cu/Cu

2

0 heterojunction

solar cells

4

or MIS-type CU/

CU

2

0

cells.

6

VI. DISCUSSION

ND

CONCLUSIONS

The

output characteristics for the ITO/Cu

2

0 photo

cells depended on the composition of both the ITO film and

the

Cu

2

0 film.

The

CuzO cells deposited by sputtering on the

ITO

films

ofB

and C type (Sn:In=85:

15)

exhibit

I V

characteris

tics as shown in Fig. 8, and the polarity

of

photovoltage is

always positive on the gold contact side. The activation ener

gy of 0.55 eV for CuzO film was found from thermostimulat

ed conductivity whereas the band gap of 2.0 eV was found

from the spectral dependence

of

the photovoltaic effect.

Therefore, we can propose a barrier band diagram for

ITO/

CuzO cells such as shown in Fig. 10.

The photovoltaic characteristics of ITO/Cu

2

0 cells

were measured under an incandescent lamp with 100

ITO

Au

FIG.

10. Energy band diagram for

ITO/Cu O

cells.

3587

J. Appl.

Phys . Vol. 54. No.6. June 1983

mW cm-

z

.

The

open-circuit voltage and the short-circuit

current were in the region 20 - 90 m V and about 50 /-LA/cm

2

,

respectively, which is unfortunate ly insufficient for practical

solar cells.

For

our data we estimated the standard photovoltaic

conversion parameters

see,

e.g., 5 of Ref. 3).

For

the illumi

nated curve labeled as B,C in Fig. 8 we obtained

oc =90

mY;

jsc

=

45/-LA/cm2,

V

mp

=48

mY;

jmp=23/-LA/cm

2

,

F F ~ O . 2 7 ;

77=10 .

This undoubtedly very low value

of

the conversion effi-

ciency

of

CU20/ITO for our thin film photocell does not,

however, finally discard the Cu

2

0 as a feasible photovoltaic

material.

For

single crystal

Cu

2

0/Cu

Schottky barrier pho

tocells conversion efficiencies

of

= 1% have been demon

strated under

AMI

illumination.

7

Even higher values

of

(up to 3%) were obtained for a monochromatic illumination

A ~ 6 7 5 mm, illumination level ~ 6 0

/ L

W/c m

2

) in our pre

vious study?

The

study

2

was carried out on single crystal

Cu

2

0/Cu

photocells. At the same time, the study of thin films CuzO/

Sn0

2

cells prepared by electrodeposition

8

again resulted in

very low values of

oc andjsc (V C ~ 5

m V

andjsc =50

-LA/

cm

2

for

AMI

conditions) comparable with our present val

ues. These results allow us to suggest that low conversion

efficiencies

of

thin films Cu

2

0 cells are related with deficien

cies

of

the presently used thin film techniques for Cu

2

0,

rather than with the cuprous oxide itself. The chief problem

here is, in

our

opinion, the high resistivity of deposited Cu

2

0

films (which limits jsc rather than limitations related with

the low barrier height.

At the same time, we have to note that our Cu

2

0 films

show the typical x-ray diffraction pattern of amorphous ma

terial see Fig. 11), and probably have a high concentration

of

recombination centers in the interfacial layer (these centers

may be related with trace impurities in ITO) which tends to

lower the barrier height

of

the junction. These two reasons

are likely to have a detrimental effect of the photovoltaic

output characteristics.

In this connection we should mention that attempts

have been made to explain the efficiency plateau of Cu

2

0

cells on the basis

of

poor barrier quality.

9

In this respect, the

special study

of

diffusion lengths in Cu

2

0 thin films may

provide a better insight into the future prospectives of cu

prous solar cells.

Figure 11 a) shows the x-ray diffraction pattern for a

Cu

2

0 film

of

5500-A thickness deposited during sputtering

at an

rf

power level

of

150 W for 30 min.

For

comparison, in Fig. 11 b)

we

show the diffraction

pattern

Cu

Ka line; A

=

1.54

A of

CuzO powder prepared

chemically. In contrast with a thin film pattern [Fig. l1(a)]

this pattern shows a more pronounced crystalline structure.

From Fig.

11

b) we determined the Miller index (1.1.1) at the

Interplanar spacing

of

d = 2.46 A assuming the cubic struc

ture.

In this study, the oxygen flow was kept constant during

the fabrication

of

ITO films. The amounts of oxygen during

M. Fujinaka and

A.

A. Sarazin

3587



7/7

------.--- r--

46

44

4

4

38

the deposition as well as during the heat annealing after de

position are important for the improving of the photovoltaic

output, since electrical resistance

is

affected strongly by both

of

them.

So,

in terms

of

preparation characteristics, the low

efficiencies

of our

cells can be reasoned by insufficient opti

mization

of

oxygen

flow

parameters. As illustrated by Figs. 5

and

6,

the

Oz

to Ar ratio has a very pronounced effect on the

conductivity of ITO and

CUzO

films.

In conclusion, we can stress that the height

of

the poten

tial barrier at junction interface is strongly influenced by the

amount

of

available oxygen during the various stages

of

the

fabrication process.

One can also tentatively attribute the very low conver

sion efficiencies observed for thin films Cu

2

0/ITO

cells to

either small diffusion length or to interface recombination

centers. Both these reasons can also act jointly and eventual

ly could be related to the above-mentioned excessive

or

defi

cient oxygen.

Keeping in mind the fact that both thin

film

compo

nents of our cells (Cu

2

0 and ITO) were produced by the same

rf

sputtering process, the system Cu

2

0/ITO could be inter

esting from the viewpoint

of

mass production, provided the

photo voltaic output could be substantially increased by the

proper control

of

the preparation conditions. As one

of

the

probable ways to increase the conversion efficiency, we can

mention here the temperature annealing

of

ITO films as well

as the use of higher purity starting materials.

3588

J. Appl. Phys. Vol. 54. No.6 June 1983

T

A

...

(

CKNOWLEDGMENTS

FIG.

II.

X-ray

diffraction patterns;

a)

for

the Cu

2

0

film of5500 A hickness deposit

ed by supplying rf power level of 150 W for

30 min;

b)

for the powder

of Cu,O

made

chemically.

This work was supported by the Natural Sciences and

Engineering Research Council of Canada. The authors also

thank N. Dalacu for technical assistance on thin film prep

aration and

B.

Diacon for help during the measurement

of

Auger characteristics.

1M.

Fujinaka and

A. A. Berezin,

Thin

Solid

Films 101,7

(1983).

2A.

A. Berezin

and

F. L. Weichman, Solid State

Commun.

37,157

(1981).

JA. A. Berezin and F.

L.

Weichman, Phys. Status Solidi A

71,265

(1982).

4J.

Herion, E. A. Niekisch, and

G.

Scharl, 14th I Photovoltaic Spec.

Conference San Diego California 1980 (IEEE, New York, 1980),

p.

453.

L. Papadimitriou, N. A. Economou,

and

D. Trivich, Sol. Cells, 3, 73

(1981).

6L.

C. Olsen, F. W. Addis,

and

R. C. Bohara, 14th I Photovoltaic Spec.

Conference San Diego California 1980 (IEEE, New York, 1980),

p.

462.

7D. Trivich, E. Y. Wang, R.

J.

Komp, and A.

S.

Kahar, 13th

I

Photo-

voltaic Spec. Conference Washington

D

c. 1978 (IEEE. New York,

1978),

p.

174.

N. A. Economou, R.

S.

Toth,

R.

J. Komp, and

D. Trivich, in

Photovoltaic

Solar Energy Conference Luxembourg 1977 (Reidel-Dordrecht,

Boston,

1978),

p.

1180.

L.

C. Olsen, R. C. Bohara,

and

M. W. Urie, Appl. Phys. Le tt. 34, 47 (1979).

IOL. E. Davis, N. C. MacDonald, P. W. Palmberg, G. E. Riach, and R. E.

Weber,

Handbook

of

Auger Electron Spectroscopy

(physical Electronics

Industries, Minnesota, 1976).

11M.

Mizuhashi, Thin Solid Films

70,91

(1980).

M. Fujinaka and A. A. Serezin

3588

journal of applied physics cuprous photovoltaic cells

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