Arsenic and Antimony Doping: An Attempt to Deposit n-type CVD Diamond
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1039-P15-01
Arsenic and Antimony Doping: An Attempt to Deposit n-type CVD Diamond Paul William May1, Martin Davey1, Keith N Rosser1, and Peter J Heard2 1 School of Chemistry, University of Bristol, Cantock's Close, Bristol, BS8 1TS, United Kingdom 2 Interface Analysis Centre, University of Bristol, 121 St. Michael's Hill, Bristol, BS2 8BS, United Kingdom
ABSTRACT We report the results of experiments that attempt to deposit n-type CVD diamond in a standard hot filament reactor using 1%CH4/H2 gas mixtures, using (i) AsH3 as a gas phase source of arsenic, and (ii) evaporated Sb or Sb(Ph)3 as a source of antimony. SIMS measurements revealed that under these conditions, neither Sb nor As is incorporated into the diamond film, and the Raman spectra, electrical conductivity and crystallite morphology remain unchanged from that of undoped diamond. These experiments confirm the predicted low incorporation efficiency for As and Sb, and we conclude that doping CVD diamond with these elements cannot readily be achieved in this manner. INTRODUCTION Finding a suitable n-type dopant is a key requirement if CVD diamond is to play a major role in future electronic devices. Previous attempts to make n-type diamond by doping with elements such as N, S or P have either been unsuccessful, or have produced films with electrical characteristics that are not adequate for many proposed devices [1]. However, recent theoretical studies [2,3] have shown that if arsenic or antimony were to be incorporated substitutionally into a diamond lattice, they may act as useful n-type dopants. In particular, these studies predict that substitutional As and Sb should possess significantly shallower donor levels in diamond than substitutional phosphorus, being ~0.4 eV and 0.3 eV below the conduction band minimum, respectively. However, the large size of these atoms compared to that of carbon has led to the commonly held belief that their incorporation efficiency into the diamond lattice may be low. This, coupled with the high toxicity of As and Sb compounds, and the worry that they may permanently contaminate expensive CVD reactors, has meant that no experiments have been reported in the literature on their use as dopants for CVD diamond, despite them being quite commonly used in the Si industry. Implantation experiments using As have been reported [4,5] which show that about half of all the implanted As atoms do, indeed, lie at substitutional sites. Hunn et al. [6] implanted As into single crystal diamond and produced semiconducting layers with an activation energy of 0.41 eV. However, in order to make electrical contacts with the implanted layer, high doses of boron were also implanted followed by an annealing step which graphitised the surface. Thus, there remains the possibility that some of the conductivity may result from residual unintentional B-doping. Furthermore, all ion implantation studies introduce damage and defects into the lattice which cannot entirely be annealed out [4], and therefore such experiments cannot be taken as a reliable guide
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