Photon assisted field emission from a silicon emitter

A novel method for the high-frequency modulation of a semiconductor field e mitter array (FEA), as needed by compact high power microwave and millimete r wave tubes, is qualitatively analyzed. The model examines a FEA held at t he threshold of emission by an applied gate potential from which current pu lses are triggered by the application of a laser pulse on the backside of t he semiconductor. Such an arrangement produces electron bunches ("density m odulation") at GHz frequencies without suffering from the restriction in re duced emission area and small unit cell geometry imposed by the high capaci tance of field emitters. The analysis proceeds by first developing an analy tical model of the emission from a silicon tip using a modified WKB approac h to the tunneling current, which is validated by the more exact Airy funct ion approach to solving Schrodinger's equation. The effects of band bending are explicitly accounted for. The resulting relations are used to estimate emission from a single hyperbolic structure, and generalized to an array w here a distribution in tip radii and work function is possible. Using a sim ple relationship between the incident photon flux and the resultant electro n density at the emission site, an estimation of the tunneling current is m ade. Finally, a brief description of the operation and design of such a "ph oton-assisted field emission device" is given. (C) 2001 Elsevier Science Lt d. All rights reserved.