3
ISSN 1063-7826, Semiconductors, 2007, Vol. 41, No. 12, pp. 1457–1459. © Pleiades Publishing, Ltd., 2007. Original Russian Text © A.P. Belyaev, V.P. Rubets, V.V. Antipov, 2007, published in Fizika i Tekhnika Poluprovodnikov, 2007, Vol. 41, No. 12, pp. 1477–1479. 1457 New effective technologies for preparation of thin- film materials that are promising in fabrication of high- efficiency semiconductor devices are now actively sought [1]. Synthesis in highly nonequilibrium condi- tions can be assigned to the class of the above promis- ing technologies, since such synthesis makes it possible to obtain films with excellent crystalline structure at low temperatures [2, 3]. In this paper, we report the results of studying the interphase boundaries formed in the course of synthesis from the vapor phase under highly nonequilibrium con- ditions that control to a great extent the properties of homojunctions and heterojunctions. In the experiments, we used sandwich-like struc- tures fabricated in highly nonequilibrium conditions [2] and structures obtained under conditions close to equi- librium [4]. We used small-area sheets of fluorophlogo- pite artificial mica as substrates. A layer of gold was deposited onto the fluorophlogopite. The substrate tem- perature T s was chosen so as to ensure the growth of ori- ented film. In Fig. 1a, we show an electron diffraction pattern of the layer deposited at T s = 125 K. A CdTe layer was deposited onto the Au layer at a temperature T s . The temperature T s was equal to 125 K in the case of growth under highly nonequilibrium conditions and was equal to 870–970 K (depending on the sample) in the case of growth under equilibrium conditions. In Figs. 1b and 1c, we show the electron diffraction pat- terns for the CdTe layers obtained at T s = 125 and 873 K, respectively. A CdS layer was deposited onto the CdTe layer. The technological conditions of this deposition under the highly nonequilibrium and equi- librium conditions corresponded to T s = 166 and 823 K, respectively. The crystal structure of the CdS layer can be inferred from the electron diffraction patterns shown in Figs. 1d and 1e. All technological conditions were chosen so as to ensure the attainment of oriented layers. The structures were synthesized in a single technological cycle with the synthesis from the vapor phase. The quality of interphase boundaries was assessed on the basis of the X-ray phase analysis and capaci- tance–voltage (C–V) characteristics. A DRON-2 dif- fractometer was used for the X-ray phase analysis. The X-ray diffraction patterns were identified using the ASTM database. We measured the C–V characteristics using a VM-507 impedance meter. The main results of our studies are shown in Figs. 2–4. In Fig. 2, we show the characteristic X-ray diffrac- tion patterns for the film structures obtained under con- ditions close to equilibrium (T sAu = 125 K; T sCdTe = 873 K; and T s CdS = 870, 920, 970, and 720 K), while Fig. 3 shows the X-ray diffraction pattern for a sand- wich structure grown under highly nonequilibrium con- ditions (T sAu = 125 K, T sCdTe = 125 K, and T sCdS = 166 K). Figure 4 shows a typical C–V characteristic of the structure grown under highly nonequilibrium con- ditions. It can be clearly seen in Fig. 2 that reflections from alloys are present in the X-ray patterns; this observation indicates that there is a transition layer in the sandwich structure (an alloy layer). Evidently, the appearance of this transition layer is caused by interdiffusion, which, as is known, is related exponentially to temperature. The X-ray patterns are clearly consistent with this con- clusion. The size of peaks related to alloys increased rapidly with increasing synthesis temperature. In the case of synthesis in highly nonequilibrium conditions, the mass transport in the course of the structure forma- tion is effected by solitons initiated by misfit disloca- tions in crystal lattices of the formed layer and sub- FABRICATION, TREATMENT, AND TESTING OF MATERIALS AND STRUCTURES Formation of an Interphase Boundary Under Highly Nonequilibrium Conditions A. P. Belyaev, V. P. Rubets, and V. V. Antipov St. Petersburg State Technological Institute (Technical University), St. Petersburg, 196013 Russia Submitted May 29, 2007; accepted for publication June 6, 2007 Abstract—The results of comparison studies of the CdTe–CdS interphase boundary in Au/CdTe/CdS sandwich structures synthesized on a substrate of artificial fluorophlogopite mica in highly nonequilibrium conditions (with a substrate temperature T s = 125 K) and in quasi-equilibrium conditions (T s > 720 K) are reported. The X-ray diffraction patterns and a capacitance–voltage characteristic are also reported. It is shown that highly nonequilibrium conditions allow synthesis of structures with excellent crystalline quality and with an inter- phase boundary that is no worse than in the structures grown under equilibrium conditions. PACS numbers: 68.35.Fx, 68.37.-d, 68.55.Nq DOI: 10.1134/S1063782607120147

Formation of an interphase boundary under highly nonequilibrium conditions

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Page 1: Formation of an interphase boundary under highly nonequilibrium conditions

ISSN 1063-7826, Semiconductors, 2007, Vol. 41, No. 12, pp. 1457–1459. © Pleiades Publishing, Ltd., 2007.Original Russian Text © A.P. Belyaev, V.P. Rubets, V.V. Antipov, 2007, published in Fizika i Tekhnika Poluprovodnikov, 2007, Vol. 41, No. 12, pp. 1477–1479.

1457

New effective technologies for preparation of thin-film materials that are promising in fabrication of high-efficiency semiconductor devices are now activelysought [1]. Synthesis in highly nonequilibrium condi-tions can be assigned to the class of the above promis-ing technologies, since such synthesis makes it possibleto obtain films with excellent crystalline structure atlow temperatures [2, 3].

In this paper, we report the results of studying theinterphase boundaries formed in the course of synthesisfrom the vapor phase under highly nonequilibrium con-ditions that control to a great extent the properties ofhomojunctions and heterojunctions.

In the experiments, we used sandwich-like struc-tures fabricated in highly nonequilibrium conditions [2]and structures obtained under conditions close to equi-librium [4]. We used small-area sheets of fluorophlogo-pite artificial mica as substrates. A layer of gold wasdeposited onto the fluorophlogopite. The substrate tem-perature

T

s

was chosen so as to ensure the growth of ori-ented film. In Fig. 1a, we show an electron diffractionpattern of the layer deposited at

T

s

= 125 K. A CdTelayer was deposited onto the Au layer at a temperature

T

s

.The temperature

T

s

was equal to 125 K in the case ofgrowth under highly nonequilibrium conditions andwas equal to 870–970 K (depending on the sample) inthe case of growth under equilibrium conditions. InFigs. 1b and 1c, we show the electron diffraction pat-terns for the CdTe layers obtained at

T

s

= 125 and873 K, respectively. A CdS layer was deposited ontothe CdTe layer. The technological conditions of thisdeposition under the highly nonequilibrium and equi-librium conditions corresponded to

T

s

= 166 and 823 K,respectively. The crystal structure of the CdS layer canbe inferred from the electron diffraction patterns shownin Figs. 1d and 1e.

All technological conditions were chosen so as toensure the attainment of oriented layers. The structureswere synthesized in a single technological cycle withthe synthesis from the vapor phase.

The quality of interphase boundaries was assessedon the basis of the X-ray phase analysis and capaci-tance–voltage (

C–V

) characteristics. A DRON-2 dif-fractometer was used for the X-ray phase analysis. TheX-ray diffraction patterns were identified using theASTM database. We measured the

C–V

characteristicsusing a VM-507 impedance meter.

The main results of our studies are shown in Figs. 2–4.In Fig. 2, we show the characteristic X-ray diffrac-

tion patterns for the film structures obtained under con-ditions close to equilibrium (

T

s

Au

= 125 K;

T

s

CdTe

=873 K; and

T

s

CdS = 870, 920, 970, and 720 K), whileFig. 3 shows the X-ray diffraction pattern for a sand-wich structure grown under highly nonequilibrium con-ditions (

T

s

Au

= 125 K,

T

s

CdTe

= 125 K, and

T

s

CdS

=166 K). Figure 4 shows a typical

C–V

characteristic ofthe structure grown under highly nonequilibrium con-ditions.

It can be clearly seen in Fig. 2 that reflections fromalloys are present in the X-ray patterns; this observationindicates that there is a transition layer in the sandwichstructure (an alloy layer). Evidently, the appearance ofthis transition layer is caused by interdiffusion, which,as is known, is related exponentially to temperature.The X-ray patterns are clearly consistent with this con-clusion. The size of peaks related to alloys increasedrapidly with increasing synthesis temperature. In thecase of synthesis in highly nonequilibrium conditions,the mass transport in the course of the structure forma-tion is effected by solitons initiated by misfit disloca-tions in crystal lattices of the formed layer and sub-

FABRICATION, TREATMENT, AND TESTING OF MATERIALS AND STRUCTURES

Formation of an Interphase Boundary Under Highly Nonequilibrium Conditions

A. P. Belyaev, V. P. Rubets, and V. V. Antipov

St. Petersburg State Technological Institute (Technical University), St. Petersburg, 196013 Russia

Submitted May 29, 2007; accepted for publication June 6, 2007

Abstract

—The results of comparison studies of the CdTe–CdS interphase boundary in Au/CdTe/CdS sandwichstructures synthesized on a substrate of artificial fluorophlogopite mica in highly nonequilibrium conditions(with a substrate temperature

T

s

= 125 K) and in quasi-equilibrium conditions (

T

s

> 720 K) are reported. TheX-ray diffraction patterns and a capacitance–voltage characteristic are also reported. It is shown that highlynonequilibrium conditions allow synthesis of structures with excellent crystalline quality and with an inter-phase boundary that is no worse than in the structures grown under equilibrium conditions.

PACS numbers: 68.35.Fx, 68.37.-d, 68.55.Nq

DOI:

10.1134/S1063782607120147

Page 2: Formation of an interphase boundary under highly nonequilibrium conditions

1458

SEMICONDUCTORS

Vol. 41

No. 12

2007

BELYAEV et al.

(a)

(b)

(c)

(d)

(e)

Fig. 1.

Electron-diffraction patterns for (a) Au, (b, c) CdTe,and (d, e) CdS layers synthesized at the substrate tempera-ture

T

s

= (a, b) 125, (c) 873, (d) 166, and (e) 823 K.

16

CdTeO

3

Θ

,

deg

14 12 16 14 12 16 14 12 16 14 12

TeO

2

CdTe

Cd

S

r

Cd

S

r

Cd

S

k

Cd

S

k

Cd

S

k

Cd

S

k

Cd

S

0.8

Te

0.2

Cd

S

0.1

Te

0.9

Cd

S

0.15

Te

0.85

Cd

S

0.05

Te

0.95

(a)(b)(c)(d)

Fig. 2.

Typical X-ray diffraction patterns for theAu/CdTe/CdS sandwich structures with the CdS layer syn-thesized at the substrate temperature

T

s

= (a) 870, (b) 920,(c) 970, and (d) 720 K.

41 35

Intensity, arb. units

Θ

,

deg

3739 723 21 19 17 15 13 11 9

Cd

S

r

(002) CdTe

k

(111)

Cd

S

r

(211)

~ ~

Fig. 3.

An X-ray diffraction pattern for an Au/CdTe/CdSsandwich structure with the CdS layer synthesized at thesubstrate temperature

T

s

= 166 K.

2.0

–0.20

(

C

/

S

)

–2

, 10

–11

pF

–2

cm

4

U

, V

2.1

–0.15 –0.10 –0.05 0

2.2

2.3

2.4

Fig. 4.

A capacitance–voltage characteristic of anAu/CdTe/CdS structure with the CdS layer synthesized atthe substrate temperature

T

s

= 166 K.

Page 3: Formation of an interphase boundary under highly nonequilibrium conditions

SEMICONDUCTORS

Vol. 41

No. 12

2007

FORMATION OF AN INTERPHASE BOUNDARY 1459

strate [2]. This transport takes place only in the sub-strate plane and is not conducive to mixing of materialsof the substrate and layer. At the same time, the sub-strate temperature is so low that the interdiffusion isfound to be completely suppressed; as a result, a transi-tion layer containing the alloy is not formed, which isconfirmed by the data shown in Fig. 3. It is clearly seenthat there are no peaks related to alloys in the diffrac-tion pattern shown in Fig. 3.

Additional evidence in favor of existence of anabrupt interphase boundary between CdTe and CdSformed in highly nonequilibrium conditions is pre-sented by linearization of the

C–V

characteristic in the(1/

C

)

2

U

coordinates as shown in Fig. 4.Thus, the results obtained make it possible to state

that under highly nonequilibrium conditions of growthone can not only synthesize layers with a crystallinequality no lower than those obtained under equilibriumconditions but also obtain structures with a more abruptinterphase boundary.

This study was supported by the Russian Founda-tion for Basic Research, project no. 07-03-00366.

REFERENCES

1. I. V. Bondar’, A. A. Va

œ

polin, V. Yu. Rud’, et al., Fiz.Tekh. Poluprovodn. (St. Petersburg)

41

, 160 (2007)[Semiconductors

41

, 155 (2007)].

2. A. P. Belyaev and V. P. Rubets, Fiz. Tekh. Poluprovodn.(St. Petersburg)

35

, 294 (2001) [Semiconductors

35

, 279(2001)].

3. A. P. Belyaev, V. P. Rubets, and V. V. Antipov, Fiz. Tekh.Poluprovodn. (St. Petersburg)

40

, 790 (2006) [Semicon-ductors

40

, 770 (2006)].

4. A. P. Belyaev, V. P. Rubets, and I. P. Kalinkin, Fiz. Tverd.Tela (St. Petersburg)

39

, 382 (1997) [Phys. Solid State

39

, 333 (1997)].

Translated by A. Spitsyn