THIN SOLID FILMS OF OXIDES, TIO2, FE2O3, AND SnO2, PREPARED BY ORGANOMETALLIC

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THIN SOLID FILMS OF OXIDES, TIO2, FE2O3, AND SnO2, PREPARED BY ORGANOMETALLIC

Wenxiu Luo, Zhongke Tan

To cite this version:

Wenxiu Luo, Zhongke Tan. THIN SOLID FILMS OF OXIDES, TIO2, FE2O3, AND SnO2, PRE- PARED BY ORGANOMETALLIC. Journal de Physique Colloques, 1989, 50 (C5), pp.C5-773-C5-778.

�10.1051/jphyscol:1989593�. �jpa-00229626�

JOURNAL DE PHYSIQUE

Colloque C5, supplbment au n 0 5 , Tome 50, mai 1989

THIN S O L I D F I L M S OF OXIDES, TI02, FE,O,, AND SnO, , PREPARED BY ORGANOMETALLIC

WENXIU LUO and ZHONGKE TAN

Qingdao Institute of Chemical Technology, P.R. China

Resume

-

Des films minces de Ti02, Fe203, Sn02 ont ete prepares par CVD a partir d'organometalliques. La structure et les carmteristiques de ces filrns ont ete determinees par diffraction X, microscopic electronique, diffraction eledronique et absorption UV. Le comportement photo6lectrochimique de ces dep6ts sur monocystal de silicium est egalement mention&.

Abstract

-

Thin oxide films of Ti02, Fe203-and Sn02 have been prepared by the organometallic chemical vapor deposition (MO-CVD) technique. The structure and character of these oxide films

were

determined by X-ray diffraction, electron micmscopy, electron diffraction and UV absorption.

These properties are reported. The photoelectrochemical kehavior of these filrns on silicon single crystals as electrodes are also reported.

Ti02, Fe203 and Sn02 in pure form are wide -bandgap semiconductors- (11. These films have high transparency in the visible spectral region, These oxide films have found applications in electronics, optoelectronics, solar cells and display devices [2,31. A variety of techniques, including reactive sputtering, reactive evaporation, ion-beam evaporation and chemical vapor deposition and hydrolysis of the respective halides

or

alkoxides are employed forthe growth of Ti02 Fe203 and Sn02 thin films 141: In recent years, organometalQoCVD has emerged as a successful way for the gmwth of these thin films. The MO-CVD techniques w r e used over the past several years and they have often yielded superior quality films than those grown by the conventional CVD or physical methods [l].

2- EXPERIMENTS

The equipment for obtaining equipment is showed in fig. l .

H I -

films by the MO-CVD method is quite simple, the diagram of experimental

Fig. 1 Experimental e q ~ i ~ n e f g : A. reactor B. furnace C. substrates D. source E. doped

source

F. valve G. flow meter H. exhaust

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1989593

(25-774 JOURNAL DE PHYSIQUE

Thin films of Ti02 Fe20g and Sn02 were grown by pyrolysis and oxidation of (C4H80)4 Ti Fe(C3H5)2 and (CH&Sn; with 02-N2 mixtures as carrier gas ; deposition was carried out on hot glass or silicon substrates at 300°C-480°C. The method is based on the following reactions ;

(C4 4Ti Ti02

Fe ),C(

, {Fe203 i gaseous products organic

300-480°C

(CH ) Sn Sn02

3 4

The optimal deposition conditions are listed in table l.

Table 1 : optimal deposition conditions for Ti02, Fe203 and Sn02 films

The P As and F-doped Sn02 films (thickenss-1500A) were deposited on glass at 430°C in the following conditions (table 2).

Coumpound

Ti%

Fe2 '3 Sn02

Table 2 : deposition conditions for different doped Sn02 films (A* is P, As or F) growth

temp.

("c)

400-480

300-350 4 1 0-470

T I

he

GI^uhZh

iates d these

f i b a%

sh~wii

ⁱⁱⁱ fig.2 doped films

Sn02 .P SnO

.

As

2 Sn02.F

.

source temp.

("c) 1 20

120 25

atomic ratio (A*/Sn)

0.01 0.01 0.02

flow rate of N or O2 through the source

(ml/min)

N2 60

O2 80 N2 80

flow rate of 0 2 (mllmin)

48 55 0

flow rate of 0 2 (m llm i n)

45

80 80

total gas flow rate (I/min)

1

1 1

growth rates

0

(A/

min)

500 270 800

sheet resistance (ohm/crn2)

32 38 34

transmission T (OIO)

95

86 82

The films were characterized by (D/MAX*rA) X- ray diffraction, classical scanning electron microscopy, transmission electron microscopy and by UV spectromety. The results are presented on the figures 3-4-5.

10- ₈

_- n

\m 300-

/

^{m\ 800-}

Fig.3 X-ray diffraction patterns A : Ti02 (rutile); B : Ti02 (anatase); C : a-Fe203; D : amorphous Fe2u3 E : Sn02

E-./.

200-

/ .

_\ ^700-

m

.\

4

-

0

400 500 600 700 800 300 350 400 450 400 450 500

( a ) ( b ) ( c )

Fig.2 growth rates vs substrate temperature (a) : Ti02; (b) : Fe203; (c) Sn02 T

CC)

I I I I

600-

T CC)

I I I

T ("C)

I I

JOURNAL DE PHYSIQUE

Fig.4 (a) Diffraction ring of polycfystalline Fig,4(b) Electron diffraction ring of Ti02 deposited on (1 1 1) single crystal amorphous Fe203 deposited on glass at

silicon at 480°C 450°C

Fig.4 (c) Morphology of Sn02 film deposited Fig. 4 (d) Morphology of P-doped (P/Si on (1 11) single cystai silicon at 430°C atomic ratio 0.26) Sn02 film deposited on a (1 11) single crystal silicon at 430°C

Fig.5 UV absorption s,wctmm of 1500A thick films deposited on glass a : a-Fe703; b : TiO,; c : SnO,

L L

- .

Fig.6 Variation of the photocurrent (i) in function of the potential (V vs HgO) of different films deposited on single crystal silicon as photocathode

A : C (solution) : 1 mol KOH 6 : C : lmolKOH b, b' P+/P-SVFe203 2 (a) P+/P-Si

I (photocurrent) ': 53mw cm- I : 1 l 0 m~ cmP a, a' PIP-Si v (sweep rate) : IOOmV sec- 1 (b) P+/P-SilTi02

v : 100 rnV sec-' a, b irradiated a', b unirradiated

-h

U !

- ^-l

2uol--+d&L

^- 0 ^0.6

^-

^0.8

^-

^1.0

^-

^1,2

^-

^1.4

^-

^1.6

@ ( V vs HgO

1

C : C : 0,2 mol Na2S04 I : 800 mW cm-2 v : 50 mV sec-'

1 unirradiated 2 P-Si irradiated 3 P-SEn02 irradiated

JOURNAL DE PHYSIQUE

3- CONCLUSIONS

In this paper the optimal deposition conditions for Ti02, Fe203 and Sn02 films carried out by MOCVD technique are reported. The behavior of growth rates of these films in function of substrate temperatures are similar (fig.2). The highest growth rates of Ti02, Fe203 and Sn02 films are 11.5Nmin (70OoC), 380 Nmin (400°C), 9OONmin (41 0°C) respectively.

Polycrystalline Ti02 exhibits either a rutile or anatase structure. The results of the X-ray diffraction indicate that Ti02 crystallizes with the rutile structure when the deposition occurs above 400°C and the anatase stmcture when the film grows below 400°C on single cystal (1 11) Si substrates. The polycystalline films of Fe203 are a-Fe203 when deposited at 300°C-350°C on single crystal ( l 11) Si substrates; when deposition is made at 450°C on glass substrates amorphous Fe203 is obtained. The films of Sn02 are generally polycrystalline and their X-ray diffraction patterns show a preferred orientation connected with the strongest (1 10) line. These polycrystailine films (thickness : 1500A) have a high transparency (85-95%) in the visible spectral region and show high electrical resistivities at room temperature (p

>

¹⁰ Cl. cm). Doped films (1000- 3000A thick) with square resistam values of 3040 ohrn/cm2 and light transmission up to 80-95%, in the visible spectral region can be readily prepared. The films with the P(As or F) ISn atomic ratio approaching 0.01-0.02 shox similar growth behaviour and yield maximum conductivity.

The P-doped (PISi atomic ratio 0.01) yields films of higher conductivity (32 ohm/crn2) without loss of optical transmission (95%). When the P/Sn atomic ratio is 0.25, the films exhibited rapid transition from the polycrystalline to the amorphous state fig.4(d). The photoelectrochemical properties of these films on (1 11) singie crystals silicon as electrodes were shown; the photoresponse of these films on silicon photocathode increase the potential of hydrogen evolution and shifts it to the positive direction (fig.6).

REFERENCES

[l] H. Prakash "Process Crystal Growth and Characterization", Pergamon Press Ltd. Printed in Great Britain, 6 (1 983) 371 -391

.

[2] W. Kern, E. Tracy, J. Vac. Sci. Tech.,

17

(1980) 374.

[3] A. Fujishima andK. Henda, Nature,

238

(1972) 37.

[4] J. Jarzebrki and J.P. Marton, J. Electrochem. Soc.,

123

(1 976) 199c.