Characterization of copper-diamond (100), (111), and (110) interfaces: Electron affinity and Schottky barrier

In this study ultraviolet photoemission spectroscopy was employed to correlate the electron affinity and Schottky barrier height of Cu films on type-IIb ($p$-type) diamond (100), (111), and (110) surfaces. Furthermore, field emission measurements were correlated with the effective electron affinity of the samples. Prior to deposition the diamond samples were cleaned by various annealings and plasma treatments in ultrahigh vacuum. Annealing the diamond substrates to 1150 °C resulted in adsorbate-free surfaces with a positive electron affinity. A negative electron affinity (NEA) was induced after depositing 1 Å of Cu on the clean surface. The Schottky barrier heights for the clean surfaces ranged from 0.30 eV for the (111) surface to 0.70 eV for the (100) surface. Depositing Cu onto H-terminated surfaces exhibiting a NEA still resulted in a NEA on all surfaces. However, the Schottky barrier heights were larger, ranging from 0.50 eV for the (111) surface to 0.90 eV for the (100) and (110) surfaces. The metal-induced NEA has been found to be stable to exposure to air. Following a 500 °C annealing an oxygen-terminated (100) surface with a positive electron affinity was obtained. Cu deposition resulted in a positive electron affinity and the largest Schottky barrier height with 1.60 eV. A field emission threshold field of 79 V/μm was obtained for an oxygen-terminated diamond (100) surface. Values of 20, 25, and 53 V/μm were measured for Cu on clean, H- and O-terminated surfaces, respectively. Based on these experiments, it is suggested that chemisorbed species such as H or O on diamond surfaces cause an increase in the Schottky barrier as well as in the field emission threshold field after Cu deposition.