Hydrogen and deuterium termination of diamond for low surface resistance and surface step control

Abstract

A 2D conductive hole gas in diamond is obtained by exposing diamond to a plasma formed in H2 or D2, which terminates the diamond surface with H or D. The diamond is still insulating until it is activated by exposing it to air or overcoating it by atomic layer deposition, ALD, with Al2O3/SiO2 or evaporated WO3. The carrier density of air activated diamond slowly decreases in time, days to weeks, and the carrier mobility increases. However, the carrier density deceases faster than the mobility increases and the diamond's surface resistance increases in time. The mobility is empirically related to the carrier density by a power law, mobility = Q (carrier density)-0.42, where Q is determined by fitting the equation to the data.The value of Q and the surface resistance of the 2D gas depends upon the removal of impurities such as C, K, and Na in the plasma, as well as the offcut angle from the (100) diamonds. These impurities originate from carbon on the chamber walls, the Mo structure that supports the diamond during plasma exposure, impurities on the diamond, such as H2SO4, after inefficient cleaning, and the carbon from the diamond itself as it is etched in the plasma.Once the impurities are reduced, then the offcut angle of (100) diamond to the [011]-axis generates crystal steps generally parallel to the 01¯1axis on the diamond surface. Resistance along the steps is lower than perpendicular to the steps. With the impurities removed, six (100) diamonds offcut by ~6° to the [011] axis had resistance parallel to the steps, 01¯1,vary from 1.32 to 1.95 kΩ sq.−1 with an average of 1.70 ± 0.25 kΩ sq.−1 and perpendicular to the steps, [011], from 1.93 to 3.20 kΩ sq.−1 with an average of 2.51 ± 0.4 kΩ sq.−1.