Metal site disorder in zinc tin phosphide
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Mark W. Peterson Photoconversion Branch, Solar Energy Research Institute, 1607 Cole Boulevard, Golden, Colorado 80401 D . L. Williamson Department of Physics, Colorado School of Mines, Golden, Colorado 80401
James S. Frey and Gary E. Maciel Department of Chemistry, Colorado State University, Fort Collins, Colorado 80523
B. A. Parkinson3' E. I. du Pont de Nemours and Co., Central Research and Development Department, Experimental Station E328/216, Wilmington, Delaware 19898 (Received 3 December 1986; accepted 17 April 1987) The optoelectronic properties of the II-IV-V 2 semiconductor ZnSnP 2 are studied as a function of the cooling rate of the crystal growth melt. The structure of the material, as studied by x-ray diffraction, is seen to change from chalcopyrite to sphalerite as the cooling rate is increased. Photoelectrochemical measurements show that the bandgap of the material decreases from 1.64 eV for the chalcopyrite to 1.25 eV as the structure approaches sphalerite. The ' 19Sn Mossbauer spectroscopy shows both an isomer shift and a broadening of the ' 19Sn resonance as a result of new tin environments produced by disordering of zinc and tin sites at the faster cooling rates. The 3 'P solid-state nuclear magnetic resonance spectroscopy clearly shows new resonances associated with the additional phosphorus environments produced by metal site disordering. A model based on zinc and tin site exchange with the introduction of compensating donor and acceptor states is proposed and discussed.
I. INTRODUCTION Compound semiconductors, espeically the III-V compounds, are being applied to more and more complex devices and device structures. The preparation of a device many times involves use of alloys of III-V or I I YI semiconductors to obtain the desired optoelectronic properties. Many of these ternary alloys are isoelectronic with the H-IV-V 2 ternary compound semiconductors. In this article we study a member of this class of materials, ZnSnP2. We recently applied photoelectrochemical techniques to study one member of the II-IVV2 family of semiconductors, CdSnP 2 .' While CdSnP2 is isoelectronic with the III-V binary semiconductor, InP, ZnSnP 2 is isoelectronic with the alloy In O 5 Gao 5 P (InGaP 2 ). Such alloys are usually random but there have been some recent observations of ordering in III-V alloys (Al* Ga[ _ x As and GaAs 05 Sb 05 ),2a>2b as well as a theoretical description of such ordering.20 Unlike CdSnP2, which always crystallizes in the chalcopyrite structure, ZnSnP2 can be prepared in structures showing either sphalerite, chalcopyrite, or intermediate x-ray patterns. Previous work has shown that the relative intensity of x-ray reflections, associated with the chalcopyrite form of ZnSnP2, decreases as the cooling rate of " Author to whom correspondence should be addressed.
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J. Mater. Res. 2 (4), Jul/Aug 1987
http://journals.cambridge.org
the melt from which crystals of the material are grown is increased.3 The bandgap of the material, as measured by luminescence4 and photoconductivity,5 was seen t
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