XPS study of diamond surface after mass-separated low-energy phosphorus ion irradiation

Phosphorus-ion irradiation of synthetic type II a diamond crystals with a hydrogen-terminated (100) surface was carried out by using a 40-eV mass-separated 31P+ ion beam at ion doses from 4.4×1011 to 3.4×1014 ions/cm2. The effects of the dose strength on the electrical state of the diamond surface were investigated. The diamond surface was characterized by using X-ray photoelectron spectroscopy (XPS). Work functions were determined from the XPS photoemission cutoff and valence band spectrum. The hydrogen-terminated II a (100) surface demonstrated the negative electron affinity (NEA) property, and the work function was found to be 3.9 eV. The NEA property disappeared after phosphorus-ion irradiation higher than 2.3×1012 ions/cm2, and the work function increased to 4.7 eV at 1.3×1013 ions/cm2. We believe that a new energy level is formed due to the displacement of phosphorus. Defects were introduced at ion irradiation doses greater than 3.0×1013 ions/cm2, and a defect-related energy state was formed.