Poster 14

Manish Niranjan UT-Physics

A theoretical investigation of germanides of Pt and Ni: the electronic structure, elastic properties, surface energetics, and work functions As scaling of traditional silicon based technology reaches its physical limits, a germanium channel field effect transistor (FET) is generating a lot of interest. To fully exploit transport properties of germanium, a low resistance contact technology will have to be developed based on metal germanides, much in the same way that self aligned metal silicides are used in a standard complimentary metal oxide semiconductor (CMOS) process today. Thus germanides with low n- and p-type Schottky barriers (for the use in NMOS and PMOS devices) to germanium channel need to be identified. Unfortunately, in spite of their new practical importance experimental studies of germanides are scarce, and, to our knowledge, no theoretical work exists in the literature. Germanides have complex phase diagrams with partial solubility and a combination of multiple eutectic and peritectoid behavior, and we find ab-initio calculations extremely useful in providing fundamental understanding of the structure-property relations between the crystal structure, chemical composition and atomic structure of the alloy/semiconductor interface on one hand and the Schottky barrier height on the other hand. In deep submicron regime (22 nm and below) PtGe, NiGe and their alloys appear to be promising as low barrier contacts to p-type germanium. Using density functional theory we have studied bulk electronic structure of NiGe and PtGe. Our calculated lattice constants are within 1-2% of recently reported experimental values. We also report nine elastic constants for each metal. We perform a comprehensive study of work functions, and surface energies as a function of the surface orientation. Theoretical work functions for the (001) surfaces of NiGe and PtGe are 4.6 and 4.9 eV, respectively, suggesting that NiGe, PtGe or their alloys indeed can be used as contacts to p-type germanium. We identify the growth conditions necessary to stabilize this orientation. Also we will discuss the stability of the monogermanide MnP-type phase of the alloy with respect to decomposition into other phases.