Enhanced Metallization Stability on Mercury-Cadmium-Telluride
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ENHANCED METALLIZATION STABILITY ON MERCURY-CADMIUM-TELLURIDE A. RAISANEN, G. HAUGSTAD, X. YU, G. CECCONE AND A. FRANCIOSI Department of Chemical Engineering and Materials Science University of Minnesota, Minneapolis, MN 55455 ABSTRACT Synchrotron radiation photoemission studies of ultra-thin Yb between Mercuryinterface at the barriers diffusion Cadmium-Telluride semiconductors and Ag overlayers show that the interlayers act as effective diffusion barrier only after Studies of interlayer thicknesses of 10-15 A are reached. morphology by means of photoemission from physisorbed Xe indicate that effective diffusion barriers are consistent with a model in which a continous Yb-Te reacted layer is covered by an Yb-rich layer with high alloying enthalpy for Hg. INTRODUCTION (MCT) is a pseudobinary Mercury-Cadmium-Telluride semiconducting alloy extensively used in high-performance infrared low detectors. Processing of this material is complicated by its stability, resulting, for example, in Hg loss from the interface 3 have region during contact fabrication. Our recent experimentsIdemonstrated that thin (3-18 A) Yb interlayers can be used as effective diffusion barriers at junctions between MCT and reactive 3 3 1 3 metals such as Al - , In , and Cr , with corresponding decrease in atomic interdiffusion, overlayer metal-Te reaction, and associated 3 that the Hg-depletion of the MCT surface. We have proposedIdiffusion barrier effect derives from the superior thermodynamic of the MCT/Yb reaction products relative to the stability based on the high metal reaction products, MCT/overlayer 4 and on the calculatedl-3,5 Yb-telluride formation enthalpy alloying enthalpies of Hg and Cd in the Yb overlayer. 3 Unlike the reactive metals we have studied earlierl- , Ag exhibits reactive behavior on the MCT surface that is dominated by 6 7 long-range Ag indiffusion into the MCT lattice via Hg vacancies - , unusual reaction. The Hg-depleting Ag-Te rather than by a diffusive behavior of Ag on the MCT surface makes MCT/Ag junctions case for diffusion barriers. We conducted an interesting test synchrotron radiation photoemission studies of MCT/Ag junctions in the presence of Yb interlayers of various thicknesses.We observed a non-monotonic coverage dependence of the diffusion barrier effect on Yb thickness. Thin barriers (Yb coverage 3-5 A) are only partially effective at hindering Ag indiffusion, intermediate suddenly at high Ag work, but fail thicknesses (8 A) initially while Yb interlayers of 10-15 A thickness behave as coverages, ideal diffusion barriers. To explain the striking non-monotonic Yb we have coverage-dependence of the diffusion barrier effect, conducted studies of the coverage dependence of the interlayer morphology by means of photoemission from physisorbed Xe. To our application of this technique to the knowledge this is the first study of semiconductor metallizations.
Mat. Res. Soc. Symp. Proc. Vol. 161. @1990 Materials Research Society
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EXPERIMENTAL DETAILS The experiments were conducted using photons from the Aladd
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