Surface Electronic Properties of Diamond

Abstract

The influence of surface states, defects and adsorbates on the electronic properties of diamond surfaces are discussed. As far as surface states and reconstructions are concerned the principal crystallographic surfaces, (100), (111) and (110), are essentially understood in their adsorbate free form and also when terminated by hydrogen. The role of surface defects is addressed and the correlation between the position of the surface Fermi level and the concentration of surface defects is discussed quantitatively for p-type diamond. Hydrogen passivation leads to a negative electron affinity of diamond surfaces due to a dipole layer which is induced by the heteropolar carbon± hydrogen bonds of the surface atoms. This aspect is discussed quantitatively. Finally, an experiment in which photoelectron spectroscopy and in situ conductivity measurements were combined to elucidate the surface conductivity of diamond is described and analyzed.

The Influence of Different Surface Terminations on Electrical Transport and Emission Properties for Freestanding Single Crystalline (100) CVD Diamond Samples

“…[1][2][3] It is known that an hydrogen termination of the diamond surface gives rise to a high p-type surface conductivity and to a negative electron affinity. [4,5] Applications based on these peculiar properties of the diamond layer have been developed. Even opto-electronic applications based on the ability to emit ultraviolet (UV) light have already been fabricated.…”

Influence of Surface Properties on the Quantum Photoyield of Diamond Photocathodes

“…Use of appropriate sensitivity factors shows that the O:C ratio, assuming a uniform composition in the sampling depth, is 0.032. High resolution C1s and O1s spectra are shown as insets; the C1s spectrum displays a small shoulder displaced about 0.5 eV to higher binding energy of the main peak, attributable to adsorbed hydrocarbons [1]. During exposure to laboratory atmosphere, the oxygen concentration gradually increased to a O:C ratio in XPS around 0.1, indicating this is the process which is responsible for the decrease in photocathode performance.…”

“…3 for samples subject to differing surface treatments. All of the samples show a "bulk" C1s peak, which we use as the reference binding energy, and a peak shifted to þ0.5 eV attributable to adsorbed hydrocarbon [1]. The adsorption of oxygen on the surface results in an increasing contribution to the overall intensity of the C1s signal, attributable to the growth of a new peak shifted by about þ1.3 eV.…”

“…Diamond is of interest as a material for electron emission devices since it displays a negative electron affinity (NEA) in certain circumstances [1]. The use of diamond in potential device applications, such as field emission displays and secondary electron emitters, has thus been explored.…”

“…High quantum photoyields thus require long carrier diffusion lengths to permit the thermalised electrons in the conduction band to diffuse to the surface, and a NEA to allow efficient subsequent escape into the vacuum. Detailed threshold photoemission studies using single crystal diamond samples have been carried out, indicating that these conditions can be satisfied and that high photoelectron emission currents can be obtained, provided the crystal is terminated with chemisorbed hydrogen [1,5]. Much less is known concerning CVD diamond, which is probably the only diamond material of interest commercially for large area photocathodes.…”