Search

Field emission properties from hydrogen-terminated intrinsic diamond covered by adsorbate films are characterized as a function of surface adsorbate coverage and bulk doping with n- and p-type. The threshold of field emission from the undoped intrinsic diamond is lower than from p-type doped diamond, which is attributed to electrons arising from a two-dimensional density of state (2D-DOS) at the surface of diamond. The emission current saturates toward higher fields ("plateau"), which indicates a depletion of the 2D states. For even higher fields, the emission current rises again due to electron tunneling from the valence band. After thermal treatment of the adsorbate film to vanish surface conduction, the emission current is completely quenched since the 2D-DOS has been removed and diamond becomes fully insulating. These data are compared with p- and n-type diamonds, which show a continuous rise of emission current as a function of electric filed. Calculations based on the Fowler-Nordheim equation reveal a 2D-quantized energy level in the surface conductive layer.

Nano-structured phosphorus-doped diamonds were fabricated for field emitters and their field emission properties were characterized. Two kinds of nano-structures were prepared; tip array structures and whiskers on tip structures. The tips, which have 100 nm radius and 10 µm height, are used in tip array structures; whiskers have tip radii of 5 nm and height of 500 nm. Following nano-structure formation, a reduction of threshold fields is observed compared to non-patterned flat surfaces. This is ascribed to field concentration at the tips. However, at higher electric fields, a saturation of the emission current is observed due to non-negligible bulk resistances in tips and whiskers.

In this study, the field emission properties of P-doped diamond with various surface treatments were measured in order to understand the effects of surface treatments on the barrier height. The emission properties were acquired for diamond with C-reconstructed, oxidized, and H-plasma treated surfaces. The voltage drop across the vacuum was estimated for each surface, using threshold voltage-anode distance (V-d) measurement. The estimated electric fields near the diamond surface were 4.95, 26.6, and 54.1 V/mm for the C-reconstructed, oxidized, and H-plasma treated surfaces, respectively. The barrier height ratio of these surfaces derived from their electric fields was 1 : 3:1 : 4:9, which agrees with the result derived from Fowler-Nordheim plots. Considering the electron affinities of all surfaces and the obtained results, positive electron affinities dominate the field emission properties of the C-reconstructed and oxidized surfaces. An internal barrier due to upward band bending on the H-plasma treated surface limits the field emission properties, even though it has a negative electron affinity. Our results suggest that the emission properties strongly depend on the barrier height, which is modified by surface treatment.