A Tem Investigation of Secondary Dislocations in Grain Boundaries in Germanium
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A TEM INVESTIGATION OF SECONDARY DISLOCATIONS IN GRAIN BOUNDARIES IN GERMANIUM M. GRIESS, M. SEIBT AND H.J. MOLLER* IV. Physikalisches Institut, University of Gottingen, 3400 Gottingen, FRG * Department of Materials Science and Engineering, Case Western Reserve University, Cleveland,Ohio 44106, USA ABSTRACT
Germanium bicrystals containing dissociated low energy grain boundaries with a common [0111 tilt axis were studied. The dislocation structure of a grain boundary with a misorientation of about 280 has been investigated in detail and could be interpreted as a near-coincidence E27 - tilt grain boundary. Both conventional and high-resolution techniques were applied to analyze the Burgers vectors of the secondary dislocation network. In all cases non - primitive Burgers vectors were observed. The comparison with previous results indicates that the Burgers vectors of the dislocation network may depend on the degree of misorientation of the bicrystal. INTRODUCTION The electronic properties of polycrystalline semiconductors are to a great extent determined by the energy levels in the band gap which are introduced by grain boundaries. Structural features like dislocations, steps or precipitates have been related to the electrical activity of the grain boundaries [1-3]. Since the complexity of random grain boundaries hampers their investigation coincidence and near-coincidence grain boundaries in elemental semiconductors have been mainly investigated so far [4]. Of particular importance are dislocations in grain boundaries which seem to introduce not only additional deep levels [5] but can also be attractive sites for segregating impurities [6]. It is therefore desirable to obtain more insight into the structures of secondary grain boundary dislocations. This paper presents a structural investigation of a near - coincidence [011] tilt grain boundary in germanium. The network of the secondary dislocations could be partly analyzed by conventional and high resolution TEM.The problems connected with the analysis of complex dislocation networks in grain boundaries will be discussed. EXPERIMENTAL PROCEDURE Bicrystals were grown by the two seed Czochralski technique from high purity germanium. The [0111 - oriented seed crystals were rotated around the common [011] axis by about 420 to produce a symmetric near - coincidence Z9 tilt grain boundary. This angle is about 30 off the exact E9 coincidence orientation at 38.940. The growth often resulted in a dissociation of the near - 1:9 grain boundary into a pure Z 3 twin boundary and a grain boundary with a misorientation of approximately 280 which lies between a Z 19 and a Y.27 coincidence orientation. It was this grain boundary that was used for the further analysis. The deviation of the two grains from the coincidence orientations which had to be measured very accurately was determined in the TEM by measuring the splitting of corresponding diffraction spots in both grains and the shift of corresponding Kikuchi lines. Both methods yielded similar results with an accuracy of 0.10.
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