On Enabling Nanocrystalline Diamond for Device Use: Novel Ion Beam Methodology and the Realization of Shallow N-type Diamond

Abstract

Despite the many superior attributes of diamond, electronic device performance to date has fallen well behind theoretical expectation. The potential realization of highly efficient electronic polycrystalline diamond devices has been more than limited by certain technological challenges such as maintaining efficient/shallow n-type doping without higher density of defects or incorporation of sp2 bonded carbon as a result of doping(during ion implantation process). Specific n-type diamond reports demonstrating phosphorus doping (with activation energy reported in the range of 485 meV to 600 meV in (100) oriented systems have been particularly problematic as a lower solubility is found as compared to (111) oriented synthesis efforts, in addition to the reported self-compensating nature. Amongst the previous reports of Phosphorus-doped diamond nearly all experimental reports to date show visual crystallographic dislocation/pitting on the (100) facet with even moderate doping where dislocations have been observed to be incorporated into the bulk volume during growth. These dislocations, which are known carrier scattering sites, subsequently lower mobility rendering poor conductance and high resistivity. Due to this well-known sensitivity of phosphorus incorporation to the crystal quality, typically lower in polycrystalline than homoepitaxial films, polycrystalline-based experimental reports have been largely absent. With respect to Phosphorus in-situ doping based efforts, rendered films demonstrate both the visually identifiable pitting and electronically identifiable poor conduction characteristic, and with respect to ion beam doping efforts, complete graphitic flaking at even moderate doses (i.e. greater than 3×10¹⁷cm⁻³). Motivated by these shortcomings and the success of recent experimentation, we present the methodology and data from our recent successful fabrication of polycrystalline diamond P⁺-i-N junction (diode) with high crystal quality, high power handling capability, high current density, low threshold voltage, and ohmic contact, under room temperature operation, previously undemonstrated across all diamond material types. The superior electrical performance of the device was obtained by novel ion beam methodology designed to resolve previously unaddressed issues relating to n-type doping of diamond materials. A high current density of approximately 10⁴ A/cm² is attained at 20V forward bias.