Band diagram for chemical vapor deposition diamond surface conductive layer: Presence of downward band bending due to shallow acceptors

The properties of surface conductivity (SC) of impurity-non-doped CVD diamond (001) samples were studied by various methods of sheet-resistance (R_S) measurement, Hall-effect measurement, XPS, UPS, SES, SR-PES, PEEM and 1D band simulation taking into account special emphases on deriving the information about the surface band diagram (SBD). The R_S values in UHV conditions were determined after no-annealing or 200 ～ 300 °C annealing in UHV. C 1 s XPS profiles were measured in detail in bulk-sensitive and surface-sensitive modes of photoelectron detection. The energy positions of valence band top (E_V) relative to the Fermi level (E_F) in UHV conditions after no-annealing or 200 ～ 300 °C annealing in UHV were determined. One of the samples was subjected to SR-PES, PEEM measurements. The SBDs were simulated by a band simulator from the determined R_S and E_V ? E_F values for three samples based on the two models of surface conductivity, namely, so-called surface transfer doping (STD) model and downward band bending with shallow acceptor (DBB/SA) model. For the DBB/SA model, there appeared downward bends of SBDs toward the surface at a depth range of ～ 1 nm. C 1 s XPS profiles were then simulated from the simulated SBDs. Comparison of simulated C 1 s XPS profiles to the experimental ones showed that DBB/SA model reproduces the C 1 s XPS profiles properly. PEEM observation of a sample can be explained by the SBD based on the DBB/SA model. Mechanism of SC of CVD diamonds is discussed on the basis of these findings. It is suggested that the STD model combined with SBD of DBB/SA model explains the surface conductivity change due to environmental changes in actual cases of CVD diamond SC with the presence of surface E_F controlling defects.