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GROWTH OF AU ON A GE (111) SURFACE D.N. DUNN, P. XU AND L.D. MARKS Department of Materials Science & Engineering, Northwestern University, 2145 Sheridan Rd., Evanston, I1.60208 ABSTRACT We investigate the room temperature growth of evaporated Au thin films on both clean and dirty single crystal Ge (111) substrates. The annealing behavior of these films was then examined under low and high temperatures. INTRODUCTION The growth of noble metals such as Au and Ag on Si and Ge is of considerable interest for modem semi-conductor device applications. Several groups have investigated the room temperature growth of Au films on Ge (111) substrates using RHEED [1-3], LEED [4-5], UPS [6], as well as other techniques. It is clear from these investigations that the growth of Au on Ge (111) proceeds by a mechanism contrary to what might be expected by comparison to the growth of Au on Si (11). In general most of these studies can be looked at in two regimes, the first being simple room temperature growth over a wide range of Au coverages from a few tenths of a monolayer up to 100 A in thickness. The second regime is the behavior of these Au films as a function of annealing temperature. Using RHEED and LEED to study a wide range of Au coverages, Le Lay [1-3] and coworkers have found that the growth mechanism of Au films proceeds by the appearance of two dimensional close packed domains which do not completely cover the surface. These domains do not give good LEED patterns which would imply that they are relatively small, i.e., less than 100 A across. For higher coverages it was found that the two dimensional domains initially increase in size and then proceed by a layer by layer growth mechanism normal to the Ge substrate. Upon annealing [3] at temperatures greater than 100 "C, the two dimensional domain structure of the Au film is seen to form three dimensional epitaxial crystallites where Au (111)//Ge (111). The formation of three dimensional crystallites was also found to clean the substrate. The interface between Au and Ge has been examined in an effort to understand the differences in growth of Au on Ge versus the growth of Au on Si. Perfetti et al. [6] have examined this interface using UPS and found that two distinct Au - Ge phases are formed during the growth process which depend upon the Au coverage. One of these phases is a stoichiometric Au-Ge phase while the other is a nearly pure Au phase. This is in contrast to the Au on Si case where above a critical thickness it is found that Si and Au atoms interdiffuse forming an amorphous alloy whose composition depends on the film thickness up to a maximum of 20 monolayers [7-8]. We investigate the growth of room temperature Au films on Ge (Ill) substrates by evaporation where the total film thickness is less than 100 A. Two types of Ge substrate are used, the first is a clean single crystal Ge (111) crystal where a (2xn) reconstruction was established prior to evaporation. The second type of substrate is a dirtier substrate where there were small amounts of amorphous carbon a