ION-IMPLANTED STRUCTURES AND DOPED LAYERS IN DIAMOND

With the advent of, and growing interest in, metastable diamond growth by means of plasma-assisted chemical vapour deposition, the possibility of using such substrates for electronic and opto-electronic devices became a relevant topic. Even before this development, various attempts have been made to dope diamond owing to the attractive properties which this material possesses; like, for example, its high heat conductivity. Progress has been hampered by the thermodynamic instability of diamond at ambient conditions, which necessitates extremely high pressures to stabilize it at the temperatures needed for standard doping processes, comparable to those routinely used for silicon and germanium. Since its inception, ion implantation has been considered as the most feasible method to change the electrical properties, within preselected regions, of a diamond substrate. Some of the first results reported, nearly three decades ago, proved to be overly optimistic, and it is now clear that the residual radiation damage, after implantation and annealing, can affect the electrical properties, induced by this process, in a misleading manner. Steady progress in understanding the mechanisms involved, when implanting and annealing diamond substrates, has since been achieved. Presently, boron-doped layers can be generated which approach the quality found in natural semiconducting diamonds. It is also possible to manufacture diode interfaces, and this places active devices within reach. In this report, an overview is given of the past development and current status of, mainly, those investigations, on ion implantation into diamond substrates, which were aimed at changing the electrical properties by the insertion of suitable dopant atoms.