The semiconductor field-emission photocathode

Abstract

Absfracf-The recently developed large-area field-emission photocathode is described. It consists of a finely spaced array of point emitters fabricated by etching of p-type silicon or other semiconductor. Uniform emission over areas of 6-7 cm2 have been obtained. For Si, the spectral response extends from 0.4 to 1.1 pm. Quantum yields of 25 percent at 0.86 pm have been measured, which is about five times the value reported for the extended S-20 photocathode and comparable to the best 111-V photoemitters. Calculations indicate that quantum yields of up to 40 percent at 0.86 rm and 28 percent at 0.9 pm are attainable with the present photocathode structures. For low dark current densities, photocathode cooling to temperatures approaching 77 IC must be employed at present. The dark current is shown to be dominated by surface-generated electrons in the space-charge region of the emitters. Effects of phosphorus gettering and annealing treatments on dark current are discussed, and the spatial frequency response of the device is determined. The results of a computer study show that the field intensification factor of p-semiconductor field emitters behaves quite differently from that of metallic emitters.

Fabrication and characterization of p-type silicon field-emitter arrays for lithography

“…Figure 10 shows the increase in dark current with decreasing doping level ͑larger resistivity͒. The dark current is partly generated at surface states; 6,16 this effect is well known for p-n junctions in metal-oxide-semiconductor devices. The surface states exist mainly on the Si SiO 2 interface where there is a structural mismatch between the S lattice and the slightly larger SiO 2 lattice.…”

“…In particular, the work of Thomas, and Schroder et al, 6 Thomas et al, 14 and Thomas and Nathanson 15 Nathanson, 3 demonstrates clearly, as a function of temperature and light intensity, the occurrance of a plateau region, where the emission current is independent of extraction voltage. No measurements on microscopic individual silicon tips have been performed to date.…”

“…In such a short time, the beam delivers only a few hundred electrons. Published experimental results by Schroder et al 6 were very promising: large arrays of emitters with homogeneous and stable emission, sensitive to light with high quantum yields and, when cooled, low dark current. The authors had examined their usefulness for photocathode applications.…”

“…We performed many experiments on individual emitters and small arrays of emitters, the results of which we describe in the present paper. In order to have a theoretical context for discussing the experimental results, the next section will first describe our presently preferred model for field emission from p-type semiconductors, based both on models in the literature, especially from Arthur, 8 Schroder et al, 6 and Hirano et al 12 and on our own observations.…”

Multibeam scanning electron microscope: Experimental results

“…Photocathodes have problems with poor current stability, short lifetime, and low brightness. [12][13][14][15][16][17] Cold field emitters, on the other hand, are promising candidates due to their high brightness, small virtual source size, and low energy spread. They can be produced easily and cost effectively in a microfabricated array.…”