Ion Induced Morphological Instabilities in Ge
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ION INDUCED MORPHOLOGICAL
B. R. APPLETON Solid State Division,
INSTABILITIES IN GE*
Oak Ridge National Laboratory,
Oak Ridge,
TN 37831
ABSTRACT The characteristics of an anomalous morphological instability initiated in amorphous Ge by heavy ion bombardment are reviewed and a model based on defect-production/defect-interactions is proposed.
INTRODUCTION A series of recent measurements have shown that heavy ion irradiation of Ge near room temperature induces a drastic morphological change in the 2 ion bombarded surface [1-7]. For moderate doses (1015 ions/cm ) a morphological instability is initiated in the amorphous phase of Ge which results in the formation of surface craters several hundred nanometers deep. This effect differes significantly from related defect-driven phenomena such as radiation-induced segregation, precipitation or phase instabilities in that those phenomena usually occur in binary or ternary alloys where preferential coupling of certain alloying elements to defect fluxes exist, or where the number of alternate phases available provide a variety of interaction channels for decay of the disordered system (8]. The Ge effect is an instability that occurs entirely in a single phase system, namely, amorphous Ge. Also the drastic nature of the morphological alteration has no direct parallel. In this paper we review experimental results which characterize this effect. Results published elsewhere are referenced but not reviewed in detail to allow speace for speculation on the defect and materials interactions which could account for the observed morphological alterations.
CHARACTERISTICS OF THE EFFECT High purity Ge(100) and (111) single crystals from several different suppliers were implanted with He, Si, Ge, In, Sn, Sb, Tl, Pb, and Bi at 2 doses ranging from 1013_1017 ions/cm and at Ge sample temperatures from -10-800 K. Subsequent analysis included ion scattering, ion channeling, nuclear reaction analysis, optical and transmission electron microscopy, ESCA, SIMS, SEM, and surface profilometry measurements. Some implanted samples were exposed to air before any analysis, while others were analyzed in situ by ion beam analysis techniques to deduce the effects of air exposure [1-7]. The anomalous behavior of Ge was discovered during studies comparing implantation and annealing effects in Ge and Si [1]. When Si is implanted 2 with virtually any species to doses from 10 14-1017 ions/cm the near surface of the single crystal is turned amorphous. The thickness of the amorphous layer is less for 300 K implantation compared to 70 K due to increased defect mobility and recombination at the higher temperature. Not surprisingly, there is no loss of dopant other than that from normal sputtering at either temperature. *Research sponsored by the Division of Materials Sciences, U.S. Department of Energy under contract W-7405-eng-26 with Union Carbide Corporation.
Mat. Res. Soc. Symp. Proc. Vol. 27 (1984) OElsevier science Publishing Co.,Inc.
196
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