On the kinetics of sapphire charging and luminescence under electron irradiation

The paper presents experimental data on the kinetics of charging and cathodoluminescence (CL) of single-crystal sapphire under electron irradiation. We give a new explanation for the previously found effect of the delay in surface potential development during charging of single-crystal sapphire by an electron beam, and simultaneous increasing of CL intensity. Such a delay can be explained by a gradual accumulation of negative charge in the sapphire volume, which volume is larger than the initial electron-solid interaction region, together with high secondary electron emission. Such charge spreading leads to an increase in the CL intensity throughout the surface potential delay. A hypothesis is suggested that the delay time is determined by the initial number of electron traps. Subsequently, when sufficient charge is accumulated, a retarding electric field arises inside the sample, leading to a decrease of the region of negative charge localization and almost complete neutralization of the positive charge. • CL intensity and surface potential values changed together under electron beam. • F + optical line intensity increased, Ti + and Cr + lines decreased during charging. • A model involving charge spreading and its capture by traps is suggested. • Once the captured charge blocks electrons movement towards depth. • Then surface potential abruptly increases, and the CL decreases.