Multiple electron beam generation from InGaN photocathode

A p-type InGaN grown on a double-side polished sapphire substrate was used for the photocathode. The surface of p-InGaN was cleaned by heating in the vacuum chamber with a base pressure of 5×10-9 Pa. Cs and O2 were alternately supplied on the surface for activation of the photocathode(3). The quantum efficiency immediately after the activation process was 14%. The electron gun test system was composed of a cathode electrode, an anode electrode, an electrostatic lens, and a fluorescent screen. The voltages applied to the cathode electrode and the electrostatic lens were -15 and -8.6 kV, respectively. A Gaussian-distributed laser with a wavelength of 405 nm was diffracted by liquid crystal on silicon, divided into 25 laser beams, and irradiated on the InGaN photocathode from its backside. Each laser beam had Gaussian distribution with a diameter of 30 μm and an interval of 310 μm (Figure 1(a)). The generated multiple electron-beam was observed by the fluorescent screen. Deviations in the diameter of each electron beam was evaluated.