Phase relations in the Si-ZnAs2 system in the range 45-100 mol % ZnAs2

Article abstract of DOI:10.1134/S0020168509120012

The Si-ZnAs₂ pseudobinary join of the Zn-Si-As system has been studied using physicochemical characterization techniques. It contains a congruently melting compound of composition ZnSiAs₂ and has two eutectics: Si-ZnSiAs₂,

Full text of DOI:10.1134/S0020168509120012

ISSN 0020-1685, Inorganic Materials, 2009, Vol. 45, No. 12, pp. 1321–1325. © Pleiades Publishing, Ltd., 2009.
Original Russian Text © S.F. Marenkin, I.V. Fedorchenko, G.G. Shabunina, T.A. Kupriyanova, 2009, published in Neorganicheskie Materialy, 2009, Vol. 45, No. 12, pp. 1413–
1
417.
Phase Relations in the Si–ZnAs System
2
in the Range 45–100 mol % ZnAs2
S. F. Marenkin, I. V. Fedorchenko, G. G. Shabunina, and T. A. Kupriyanova
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
e-mail: marenkin@rambler.ru
Received February 16, 2009
Abstract—The Si–ZnAs pseudobinary join of the Zn–Si–As system has been studied using physicochemical
2
characterization techniques. It contains a congruently melting compound of composition ZnSiAs and has two
2
eutectics: Si–ZnSiAs , at 55 mol % Si + 45 mol % ZnAs , with the melting point at 1010°C, and
2
2
ZnSiAs −ZnAs , at 93 mol % ZnAs + 7 mol % Si, melting at 730°C. The solubilities of the end-members in
2
2
2
ZnSiAs are within 1 mol %.
2
DOI: 10.1134/S0020168509120012
INTRODUCTION
In this work, we focus on another II–IV–V com-
2
pound semiconductor: zinc silicon diarsenide,
There is currently considerable interest in the new
ZnSiAs . The choice of this compound was prompted
2
field of solid-state electronics that relies on the possibil-
ity of spin-oriented electron transfer from a ferromag-
net to a nonmagnetic semiconductor, which is expected
to evolve into single-electron logic circuits and spin
information systems in which an electron’s spin will
serve as a memory cell: one spin, one bit [1]. Spin-
polarized electron injection from ferromagnetic metals
ensures spin polarization within 10%. At cryogenic
temperatures, higher degrees of polarization, up to
by the fact that ZnSiAs is lattice-matched to Si: even
though they crystallize in different symmetries, the
2
(
001) lattice mismatch between ZnSiAs and Si is
2
below 2%. This suggests the possibility of epitaxial
growth.
EXPERIMENTAL
To optimize ZnSiAs synthesis conditions, we stud-
2
1
00%, can be achieved in semiconductor–EuO and
ied the Zn–Si–As ternary system. Analysis of the
Zn−As, Si–As, and Si–Zn constituent binaries [5] indi-
cates that the most likely pseudobinary joins in the
Zn−Si–As system are Si–ZnAs and Zn–SiAs . Based
semiconductor–cadmium chromium chalcogenide
spinel (magnetic semiconductor) structures. Devices
that require cryogenic temperatures are, however,
inconvenient for practical application. Moreover, seri-
ous difficulties have been encountered in attempts to
produce low-resistance ferromagnetic/semiconductor
contacts. It is believed that good electrical contacts and
high electron polarization can be achieved by creating
a diluted magnetic semiconductor (DMS) with a Curie (t
2
2
on the physicochemical properties of the end-members
of these joins, the optimal approach to ZnSiAs synthe-
2
sis is to react ZnAs and Si. The choice of these reac-
2
tants is prompted by the fact that, in contrast to SiAs2
= 977°C), ZnAs
= 771°ë), which enables reproducible
the known semiconductors. Doping with transition ZnAs synthesis. In addition, the use of ZnAs + Si mix-
melts congruently, at a much lower
m
2
point above room temperature, structurally matched to temperature (t
m
2
2
metals (Mn, Cr, Fe) is thought to be the most attractive tures ensures a lower arsenic vapor pressure in compar-
way of producing DMS’s. The best results have been ison with other starting mixtures and, hence, smaller
obtained with Ga1 – xMn As nanofilms grown by molec- deviations from the stoichiometry of the ternary com-
x
ular beam epitaxy. The films were ferromagnetic, with pound.
a Curie temperature T < 170 K [2]. Spintronics
C
The starting materials for the synthesis of Si–ZnAs2
samples were silicon (Kr-0000) and presynthesized
requires DMS’s with T above room temperature. In
C
recent studies, manganese-doped II–IV–V chalcopy-
2
ZnAs . Zinc diarsenide was prepared as described else-
2
rites, in particular CdGeAs and ZnGeAs , were found
2
2
where [6], via direct melting of high-purity single-crys-
tal zinc and arsenic.
to have T 's of 355 and 367 K, respectively [3, 4].
C
1
321

1
322
MARENKIN et al.
Table 1. Phase compositions of Si–ZnAs alloys (DTA, structural analysis. The chemical composition of sev-
2
XRD, and microstructural analysis results)
eral samples was determined by X-ray fluorescence
(XRF) analysis.
Composition, mol % te, °C tL, °C Phase composition
DTA scans were performed with a PRT-1000M pro-
grammed temperature controller (visualization of heat-
ing and cooling curves on an Endim XY chart recorder)
and NTR-72 pyrometer. The temperature was moni-
tored with a Pt/Pt–Rh thermocouple, which was cali-
brated against Sn (232°C), Zn (419°C), Sb (630°C),
NaCl (800°C), and Cu (1083°C). The reference sub-
stance used was calcined Al O . Heating curves were
ZnAs2
–
771
ZnAs2
9
9
9
8
8
7
6
5
5
4
4
*
7% ZnAs + 3% Si
730
732
760 ZnAs + ZnSiAs
2 2
2
2
3
3% ZnAs + 7% Si
–
ZnAs + ZnSiAs *
2
2
2
2
2
2
2
2
measured to 1130–1150°ë. Weighed amounts (1 g) of
the alloys to be studied were placed in graphitized
Stepanov vessels, which then pumped down to a resid-
0% ZnAs + 10% Si 725
807 ZnAs + ZnSiAs
2
2
–3
ual pressure of 10 Pa and sealed off. Because of the
high primary crystallization temperature of silicon in
5% ZnAs + 15% Si 738
885 ZnAs + ZnSiAs
2
2
the composition range 0–40 mol % ZnAs , we studied
2
for the most part ZnSiAs –ZnAs samples.
2
2
0% ZnAs + 20% Si 740
900 ZnAs + ZnSiAs
Microstructures were examined on an Epiquant
metallographic microscope. Specimens were prepared
by grinding and polishing with GOI paste or ASM 3/2,
M 0.5/0, and ASM 0.5/1 diamond pastes (RF State
Standard GOST 25593-83) and were then boiled in ace-
tone in a flask with a reflux condenser for 10 min. Next,
the specimens were then etched with potassium bichro-
2
2
0% ZnAs + 30% Si 725
1010 ZnAs + ZnSiAs
2
2
0% ZnAs + 40% Si 740
1060 ZnAs + ZnSiAs
2
2
mate or a 2 : 15 : 5 mixture of HF, HNO , and
3
2% ZnAs + 48% Si
–
–
–
1080
1096
1050
–
ZnSiAs2
ZnSiAs2
2
CH COOH for 5–30 s. After etching, the specimens
3
were thoroughly washed with deionized water and ace-
tone or ethanol.
XRF microanalysis was performed on an EAGLE
III μ-Probe (Rh-anode tube, V = 30 kV, I = 1000 mA).
Elemental compositions were determined by the funda-
mental parameters method using EDAX No Standards
software. The accuracy in the major components was
0% ZnAs + 50% Si
2
8% ZnAs + 52% Si
Si + ZnSiAs2
Si + ZnSiAs2
2
5% ZnAs + 55% Si 1010
2
5
%.
Phase composition was determined by XRD on
Eutectic.
DRON-1 (Ni-filtered ëuä radiation), DRON-2, and
α
Siemens Kristalloflex D5000 diffractometers. XRD
patterns were collected in the angular range 2θ = 10°–
The synthesized zinc diarsenide and silicon were
9
0°. Interplanar spacings (d) in the alloys studied were
thoroughly ground and mixed. The mixtures were compared to those in reference samples and to the
placed in ampules, which were then pumped down to a JCPDS PDF data for the Zn–Si–As system.
–3
residual pressure of 10 Pa and sealed off. The samples
were synthesized in several steps. First, the temperature
RESULTS AND DISCUSSION
was raised to the melting point of ZnAs (771°C) and
2
The DTA, XRD, and microstructural analysis
maintained there for 24 h. Next, the samples close in
results for the Si–ZnAs join are summarized in Table 1.
2
composition to ZnSiAs were heated to its melting point
2
Figure 1 presents the melting diagram of this join. The
Si–ZnAs join is seen to be pseudobinary, with a eutec-
tic phase diagram. It contains a compound of composi-
(1096°C). The other samples were heated to 10–20°ë
2
below this temperature and held there for at least 8 h in
order to homogenize the mixtures. After that, the sam-
ples were furnace-cooled.
tion ZnSiAs , which melts congruently at 1096°ë. Ear-
2
lier, its melting point was variously reported to be from
1
067 [7] to 1096°ë [8]. The Si–ZnSiAs eutectic is
Phase relations were studied by differential thermal
2
analysis (DTA), X-ray diffraction (XRD), and micro- located at ꢀ45 mol % ZnAs + 55 mol % Si and melts
2
INORGANIC MATERIALS Vol. 45 No. 12 2009

PHASE RELATIONS IN THE Si–ZnAs SYSTEM
1323
2
t, °C
T, K
1
1
1
1
1
1
400
300
200
100
000
1670
L
2
1570
1470
1370
1270
1170
1070
970
ZnSiAs
2
t = 1096°C
m
L + Si
e1
ZnSiAs + L
2
tm ZnAs2
771°C
=
9
8
7
6
00
00
00
00
ZnSiAs + L
2
e2
Si + ZnSiAs2
L + ZnAs2
ZnSiAs + ZnAs
2
2
870
Si
10
20
30
40
50
mol %
60
70
80
90
ZnAs2
Fig. 1. Melting diagram of the Si–ZnAs join: (1) DTA data, (2) microstructural analysis data.
2
at 1010°ë. The ZnSiAs –ZnAs eutectic is located at at 730°ë. The composition of the latter eutectic was
2
2
9
3 mol % ZnAs + 7 mol % Si, with the melting point refined by the Tammann method and XRF. Microstruc-
2
tural analysis (Fig. 2) and XRD results confirm that the
only phases in the ZnSiAs –ZnAs system below the
2
2
solidus line are ZnSiAs and ZnAs . The samples repre-
2
2
Table 2. Lattice parameters of the samples close in composition
to ZnSiAs2
sented in Fig. 2 contain ZnSiAs (light areas) and the
2
ZnSiAs –ZnAs eutectic (dark areas). The eutectic con-
tent has a maximum at 7 mol % Si (Fig. 2a). The XRD
2
2
Sample.
a, Å
c, Å
c/a
V, Å3
results for the Si–ZnSiAs samples indicate the pres-
2
ence of only two phases: Si and ZnSiAs2.
ZnSiAs [8]
5.609
5.609
5.608
5.609
10.878 1.9394 342.23
10.878 1.9394 342.23
10.888 1.9415 342.42
10.883 1.9403 342.39
2
Zinc silicon diarsenide has a narrow homogeneity
range: the Si and ZnAs solubilities in ZnSiAs are
2
2
ZnSiAs2
within 1%. This estimate was inferred from microstruc-
tural analysis results and from the lattice parameters of
the samples close in composition to the ternary com-
pound (Table 2). Their lattice parameters are seen to
ZnSiAs + ZnAs
2
2
coincide with those of undoped ZnSiAs to within
ZnSiAs + Si
2
2
±0.005 Å and to agree with earlier results [9].
INORGANIC MATERIALS Vol. 45 No. 12 2009

1
324
MARENKIN et al.
(
a)
(b)
Eutectic
Eutectic
ZnSiAs2
(
c)
(d)
Eutectic
ZnSiAs2
Eutectic
ZnSiAs2
Fig. 2. Microstructures of the Si–ZnAs samples containing (a) 7, (b) 10, (c) 20, and (d) 30 mol % Si; 400×.
2
CONCLUSIONS
The Si–ZnAs join was shown to be pseudobinary,
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