Controlling the carrier density of surface conductive diamond

Abstract

By placing a diamond in a H2 plasma and exposing it to air or overcoating it with Al2O3/SiO2, evaporated WO3, or other transition metal oxides a 2 dimensional, 2D, conductive hole gas forms on the diamond surface. Field effect transistors, FETs, made using this 2 D hole gas have the potential of replacing GaN FETs for use in high-power switching and high-frequency power applications. To achieve this goal, it is necessary to control the hole carrier density. When the carrier density is too high the device cannot be turned off and will have a low operational drain voltage due to electric-field break-down of diamond. On the other hand, too low a carrier density results in limited drain current, reduced power handling capability, and high on resistance. For diamond surface FETs using Al2O3/SiO2 as a gate oxide a carrier density between 1 × 1013 to 6 × 1013 cm−2 is the most desirable, depending on the intended operating voltage and the drain current density.This article discusses H-terminated procedure to controllably vary the carrier density from 1 × 1013 to 6 × 1013 cm−2. This is accomplished by varying the H-termination parameters; temperature, termination time, H2 pressure, and the microwave plasma power. During termination the diamond surface is etched and the density and type of crystal sets that form on the diamond surface is determined by these parameters. A model is presented of how the crystal step density and their character, single and double steps, can affect the carrier density.