Improvement of electron emission of silicon field emitter arrays by pulsedlaser cleaning

A diode-pumped a-switched Nd:YLF laser was used for the cleaning of microfa bricated silicon field emitter arrays. The laser wavelength was systematica lly varied from infrared to visible and ultraviolet, while the emission cur rent was measured simultaneously. Infrared (lambda = 1047 nm) or visible (l ambda = 523 nm) laser irradiation did not alter the emission behavior. Ultr aviolet laser irradiation at lambda = 349 nm, on the other hand, resulted i n a significant increase in the emission current due to cleaning of the emi tter tip surface. Numerical simulation of the laser induced temperature ris e at the silicon surface and the wavelength dependence of the cleaning effi ciency indicate that photochemical decomposition, requiring energetic photo ns, is the main mechanism for the removal of the contaminants. However, if higher energetic photons at lambda = 262 nm (fourth harmonic) are used, a t emporary decrease in emission current during laser irradiation was observed . A simultaneous decrease of the vacuum level in the test chamber indicates that this unexpected behavior is attributable to the removal of ionized sp ecies from the silicon tip. Removal of the contaminants without ionization, therefore, appears to be an essential condition for efficient cleaning of the emitter tips and correspondingly for an increase in the emission curren t. (C) 2000 American Vacuum Society. [S0734-211X(00)03502-2].