Photon assisted field emission from a silicon emitter

Abstract

A novel method for the high-frequency modulation of a semiconductor field emitter array (FEA), as needed by compact high power microwave and millimeter wave tubes, is qualitatively analyzed. The model examines a FEA held at the threshold of emission by an applied gate potential from which current pulses are triggered by the application of a laser pulse on the backside of the semiconductor. Such an arrangement produces electron bunches (“density modulation”) at GHz frequencies without suffering from the restriction in reduced emission area and small unit cell geometry imposed by the high capacitance of field emitters. The analysis proceeds by first developing an analytical model of the emission from a silicon tip using a modified WKB approach to the tunneling current, which is validated by the more exact Airy function approach to solving Schrödinger’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 where a distribution in tip radii and work function is possible. Using a simple relationship between the incident photon flux and the resultant electron density at the emission site, an estimation of the tunneling current is made. Finally, a brief description of the operation and design of such a “photon-assisted field emission device” is given.