Dislocation Related D-Band Luminescence; the Effects of Transition Metal Contamination
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DISLOCATION RELATED D-BAND LUMINESCENCE; THE EFFECTS OF TRANSITION METAL CONTAMINATION VICTOR HIGGS*, E.C. LIGHTOWLERS* AND P. KIGHTLEY** *Physics Department, King's College London, Strand, London WC2R 2LS, UK "**Plessey Research (Caswell) Ltd, Caswell, Towcester, Northants NN12 8EQ, UK ABSTRACT Photoluminescence measurements have been made on plastically formed silicon, free from metal contamination, with dislocation densities in the range 104-108 cm-2 . Only after deliberate contamination with Cu, Fe or Ni were the dislocation related D-bands the dominant spectral features observed. TEM analysis has revealed that there are no differences in the dislocation structures before and after contamination and that there is no evidence for precipitation on the dislocations or in their strain fields. The D-band features may, therefore, be due to impurities (metal atoms or point defect complexes) trapped in the strain fields of the dislocations. INTRODUCTION A considerable effort has been devoted to the study of the D-band luminescence features which are associated with the presence of dislocations in silicon. This work has been directed mainly towards relating particular luminescence features with particular dislocation types and understanding the nature of the electronic transitions involved1 ll. A similar but more limited investigation has been made of dislocation related luminescence in germaniuml 2 1and 13 very recently in Si/Ge alloys. ] D-band features are observed in silicon containing dislocations, either as grown in, or generated by plastic deformation produced by uniaxial stress or bending. Four principal bands are observed: Dl at 812meV, D2 at 875meV, D3 at 934meV and D4 at 1.0eV 141. Detailed luminescence studiesl]l have shown that the bands Dl and D2 exhibit similar behaviour and also D3 and D4. It has been suggested that D1 and D2 may be either associated 51 with point defects in the strain fields of the dislocation or related to kinks on the dislocations[ , whereas D3 and D4 have been ascribed to electronic transitions within the dislocation core structure. Dislocation luminescence has been observed in silicon grown by MBE and has been investigated in some detail by Robbins et al[ 6 1 In a more recent investigation of epitaxial layers grown by MBE[71, where the dislocation densities were found to be in the range 103-105 as determined by defect etching, we were puzzled by the absence of any of the D-band luminescence features in the as-grown material. In the course of this work it became clear that the D-band luminescence could be produced by deliberate contamination with transition metals, in particular Cu, Fe and Ni. Although the nature of the transition metal did not have a significant effect on the shapes and energies of the D-bands, it was suggested that the luminescence might be associated with transition metal decorated as distinct from undecorated dislocations. In turn this suggested that published results on D-band luminescence from plastically deformed silicon (and possibly germanium) might also be
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