Effect of phosphorus ion implantation on electrical conductivity and local lattice distortions in diamond

Abstract

In this work, phosphorus ions have been implanted with various doses at an energy 100 keV on single crystal (100) diamond. We try to understand the local lattice distortions (disorder) induced in the implanted layer post annealing (at 850 °C) as a result of ion impact with the help of out-of-plane as well as in-plane XRD techniques and its corresponding effect on the electrical conductivity in diamond crystal. While a low dose of 1014cm−2 increases the lattice parameter along the out-of-plane direction and leads to formation of isolated point defects (mostly interstitials) in the lattice without introducing much disorder, a moderate dose of 1015cm−2 initiates the process of clustering of these defects in the implanted/defected layer. An out-of-plane tensile strain that is present in low dose case is eventually released with moderate dose implantations. With high doses of phosphorus in diamond, the crystallinity in the implanted layer drops, the damage propagates to the extent that it forms small amorphous pockets within this defected layer; although the lattice is not completely amorphous as it still retains the long range order as confirmed from X-ray absorption results. Our data indicate that the electrical transport in diamond is mainly due to substitutional phosphorus when implanted at low dose of 1014cm−2 and also highlights that damage or ‘localized amorphization’ takes place at a critical implantation dose of 1016cm−2 and therefore the critical phosphorus ion dose of 1015cm−2 (in 100 keV energy regime) i.e. a damage threshold of 8 × 1021vacancies/cm3 is the limit beyond which chances of amorphization is prevalent and the electronic properties in diamond are solely due to sp3 bond breakage.