Photo-Enhanced Hardened Flat Cold Cathodes Based on III Nitrides for Pulsed and Ultra-Fast Electron Sources

Current high-temporal-resolution electron microcopy employs the photoelectric effect to achieve electron pulses in the femtosecond range. These systems employ high-efficiency photo cathodes excited by short-pulse lasers. Field-emission cathodes based on micro-tip arrays provide an alternative approach. These field emitter cathodes are electron sources in the form of arrays of micro-fabricated sharp tips. Field emission is used to extract the electrons without heating the cathodes. However, sputtering of the tip ¿ from residual gas molecules ionized by the emitted electrons ¿ blunts the emission point, increases the required voltage, and changes the electron emission properties. Hydrogen-rich molecules tend to increase emission, while oxygen-based molecules tend to decrease emission. This project will develop, fabricate, and test ultra-high-speed, high-stability, high-current-density, photon-enhanced planar cold cathodes, based on avalanche photon/electron emission diodes fabricated from III-Nitride semiconductor materials. The high speed, high stability, and high current density of the proposed devices will be provided by employing an avalanche process based on hot electrons generated by a strong electric field when a reverse bias is applied to the semiconductor diode. Commercial Applications and other Benefits as described by the awardee: The cold cathodes should find use in fast and hardened miniature electron sources for several advanced applications, including electron microscopy, mass spectrometry, and Auger spectrometry. The technology also should be applicable to field-emission-based devices for super-ambient and harsh environments.