The growth of CdAs2 and ZnAs2 single crystals from the vapor phase

Journal of Crystal Growth 44(1978) 259—261 © North-Holland Publishing Company

LETTER TO THE EDITORS THE GROWTH OF CdAs2 AND ZnAs2 SINGLE CRYSTALS FROM THE VAPOR PHASE S.F. MARENKIN, B. HUSEYNOV, V.Y. SHEVCHENKO and N.K. BELYSKIY N. S. Kurnakov Institute of General and Inorganic Chemistry, Leninsky Prospekt 31, Moscow, USSR Received 6 April

1978

Single crystals of CdAs2 and ZnAs2 have been grown from the vapor phase.

CdAs2 and ZnAs2 are semiconductor compounds with a well pronounced anisotropy of electrical and thermoelectrical properties [1] They are of interest also because of their high optical wavelength transparency in the IR range [2]. However, on account of the lack of large single crystals the main semicon-

ductor properties of the compounds have not been thoroughly investigated. The present work deals with CdAs2 and ZnAs2 single crystal growth from the vapor phase. Since these compounds consist of two volatile components, the application of other growth techniques is difficult and, as a rule, it leads to production of single crystals with considerable structural defects which have a bad effect on electrical properties and single crystal homogeneity [3]. Single crystal growth of these compounds was carned out using pre-synthesized polycrystalline material [4]. The synthesis was done by direct melting of the compounds in stoichiometric combination 4wt%.with Glass-a general less in than 1 X 10 carbonicimpurity crucibleslevel placed quartz ampoules were used as containers. In view of the fact that CdAs 2 and ZnAs2 dissociate incongruently, the arsenic excess, calculated from the vapor pressure over the CdAs2 and ZnAs2 melts at the synthesis temperatures and the free ampoule volume, has been used to obtain single-phase material. The ampoules were pumped out to 1 X l0-~Torr and were unsoldered. The synthesis took place in a vertical furnace. The ampoules were placed into the isothermal part of the furnace with a temperature gradient of less than 1°C,which eliminated transference from the reaction zone. The synthesis temperature for ZnAs2 was 795°C and for CdAs2, 640°C.For full homogeneity, the melt was kept under these conditions of temperature for no less than 36 h. The cooling was carried out at a rate of less than 25°C/h,because higher rates give metastable phases in the case of CdAs2 and a great number of defects in the case of ZnAs2. The polycrystalline

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Fig. 1. Monocrystals of CdAs2 (magn.

x

U

3.2). 259

260

S. F. Marenkin et a!.

/ Growth of CdAs2 and ZnAs2 single crystals from

the vapour phase

Fig. 2. Monocrystals of ZnAs2 (magn. X 4.2).

substance used for single crystal growth was thoroughly identified with the help of DTA, X-ray diffraction and chemical analyses. The microstructre was investigated as well, The single crystal growth was carried out in twozone furnaces with different temperature distribu-

tions. The largest CdAs2 single crystals with dimensions of 20 X 10 X 5 mm (fig. 1) were obtained at the evaporation zone temperature (T~)of 585°Cand the condensation zone temperature (TCOfld) of 560°C. In the case of ZnAs2 synthesis, the largest single crystals were obtained at an evaporation temperature

Table 1 Temperature influence on single crystals ofCdAs2 and ZnAs2 from the vapor phase No.

Tey (°C)

Tcond (°C)

°C/cm

1 2 3 4 5 6 7 8 9 10 11 12 13

585 585 580 580 575 575 575 570 570 570 560 560 560

560 555 550 555 540 545 550 540 545 550 540 515 500

2.1 1.875 1.6 1.5 1.9 2 2.1 2.1 1.6 1.3 1.2 2.5 4

1 2 3 4 5 6 7

740 740 740 745 750 755 700

728 730 725 730 740 725 660

1.3 1.0 1.3 1.5 2.2 1.8 2.6

Most typical crystal forms CaAs2 compound Ampoule of large-bloc form Dodecahedron Cubooctahedron Truncated pyramids Prismatic needles Nucleations Pyramidal-prismatic Trihedral prisms Pyramidal-prismatic Full polycrystal transference Small plates Needle crystals Crust ZnAs2 compound Prismatic plates Prismatic plates Plates Trihedral prisms Ampoule of large-bloc form Polyhedrons No transference

Dimensions (mm)

18 7 10 10 9

X7 X4 X5 X 1 X5

X X X X X

5 3 7 0.5 3

—

10 X 5 X 2 9 X 3X 1 13 X 2 X 2 —

4 X 2 X 0.5 3 X 1 X 0.5 —

7 6 8 6 9 7 —

X 3 X4 X 3 X2 X5 X3

X X X X X X

1 1 1 1 3 2

S.F. Marenkin et al.

/ Growth of CdAs2 and ZnAs2 single crystals from

of 750°Cand a condensation temperature of 735°C (fig. 2). Table 1 shows the temperature influence on the CdAs2 and ZnAs2 single crystal dimensions and forms.

References [1] V.B. Lazarev, V.Y. Shevchenko, Y.H. Greenberg and V.1. Sobolev, Poluprovodnikovye Soedineniya Gruppy AIIBV (Nauka, Moscow, 1978).

the vapour phase

261

[2] D.N. Nasledov and V.Y. Shevchenko, Phys. Status Solidi (a) 15(1973)9.

[3] A. Hryby, Czech. J. Phys. B25 (1975) 1413.

[4] S.F. Marenkin, S.1. Maksimova, B. Huseynov and V.Y. Shevchenko, Zh. Neorg. Mater. 3 (1978) 397. [5] V. Loyns and V. Silvestri, J. Phys. Chem. 64 (1960) 266. [6] Z. Munis, M. Benavides and D. Meschi, J. High Temperature Sci. 6(1974)73.