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H8.2.1

Formation of deuterium-related shallow donors in boron-doped diamond. Jacques Chevallier1, Zéphirin Teukam1, Cécile Saguy2, Rafi Kalish2, Catherine Cytermann2, Francis Bailly1, François Jomard1, Thierry Kociniewski1, Dominique Ballutaud1, Michel Barbé1, James E.Butler3, Céline Baron4 and Alain Deneuville4. 1 Laboratoire de Physique des Solides et de Cristallogénèse, UMR CNRS 8635, 1 place A.Briand, 92195 Meudon Cedex, France 2 Physics Department and Solid State Institute, Technion, Haifa 32000-Israel 3 Naval Research Laboratory, Code 6174, Washington, DC 20375, USA 4 Laboratoire d’Etudes des Propriétés Electroniques des Solides, CNRS B.P.166, 38042 Grenoble Cedex 09, France ABSTRACT It is well known that diffusion of deuterium in boron-doped diamond results in the passivation of boron acceptors with the formation of (B,D) complexes. In this work, we show that deuteration of boron-doped diamond can induce a p-type to n-type conversion under certain conditions. The n-type conductivity is governed by the ionization of shallow donors with a ionization energy of 0.34 eV. This is well below the lowest ionization energy of donors found up to now in diamond (0.6 eV for phosphorus donors). The electrical conductivity and the electron mobility can be as high as 6 S/cm and 430 cm2/Vs at 300 K. The reversibility of the effect under thermal annealing and the necessity of excess deuterium to trigger the n-type conductivity suggest that deuterium is involved in the formation of the shallow donors. The present status concerning the understanding of their origin is discussed. In addition, we have found that, contrary to previous conclusions, deuterium can diffuse in type Ib diamond. The conditions where this diffusion is observed are presented. INTRODUCTION Diamond homoepitaxial layers grown by microwave plasma chemical vapor deposition (MPCVD) use a hydrogen-rich gas mixture of CH4 and H2 with more than 95% of hydrogen since atomic hydrogen is essential for the diamond deposition [1]. Owing to the abundance of hydrogen in the diamond growth system, it is necessary to consider the possibility of hydrogen incorporation, to investigate its influence on the electronic properties of diamond and, if any, the possibility of hydrogen incorporation during the processing steps for the fabrication of diamond-based electronic and optoelectronic devices. Hydrogen at the surface of diamond is directly responsible for the negative electron affinity of (100) and (111) diamond surfaces [2,3] and is at the origin of its surface p-type conductivity. This effect is the result of an electronic charge transfer from diamond to surface adsorbates [4]. It has been used for the fabrication of high frequency diamond-based field effect transistors [5]. Theoretical calculations have shown that hydrogen is a positive-U character impurity in diamond [6,7]. Hydrogen atoms have a donor level at Ec-3 eV and an acceptor level at Ec-2 eV [6]. As in silicon, they act as counter-dopants behaving as donors in p-type diamond and as acceptors in n-type diamond. Th