Field-assisted photoemission to 2.1 microns from a Ag/p-In0.77Ga0.23As photocathode

Abstract

Reflection-mode photoemission to a 2.1-μm threshold has been achieved from an externally biased Ag/p-In0.77Ga0.23As cathode. Quantum yield at 1.9 μm is 2×10−3 electrons per incident photon for 2.4-V bias and a cathode cooled to ∼125 K. The cathode was grown by vapor-phase epitaxy on a compositionally graded InAsP on InP (100) substrate using the hydride process.

Room temperature photoemission up to a wavelength threshold of 2.3 µm from n+-InAs0.4P0.6/p−-InAs0.4P0.6/p−-ln0.7Ga0.3As field-assisted photocathode

“…6) The first field-assisted photocathode with a longer infrared threshold wavelength was proposed and demonstrated by Bell et al in 1974. 7) Subsequently, a considerable number of studies on field-assisted photocathodes were conducted by Escher and his co-workers, [8][9][10][11][12][13][14][15] who reported a high quantum efficiency of 8% at 1.55 µm. In these cases, extremely thin Ag films were used as Schottky electrodes to allow the photoelectrons that were generated by the incident light to pass through the Schottky electrode and escape into the vacuum.…”

“…However, field-assisted photoemission beyond the infrared threshold wavelength of 1.7 µm at room temperature has not yet been reported. 10) The longest infrared threshold wavelength reported to date for the field-assisted photocathode is 2.1 µm at 150 K. 13) We previously investigated the InP/InGaAsP field-assisted photocathode, which uses a pn junction rather than a Schottky electrode, and we reported a high quantum efficiency of 5% at 1.3 µm. 16) We believe that this field-assisted photocathode with its pn junction is suitable not only for achieving high quantum efficiency performance but also for extension of the long infrared threshold wavelength.…”

“…The n + -InAs 0.4 P 0.6 contact layer and the titanium electrode on the n + -InAs 0.4 P 0.6 contact layer were etched into a mesh-type pattern by photolithography and dry etching techniques, and most of the surface area of the p ¹ -InAs 0.4 P 0.6 photoelectron-emitting layer was exposed to a vacuum, as reported previously. 13) The exposed surface of the p ¹ -InAs 0.4 P 0.6 photoelectron-emitting layer was activated using cesium and oxygen to lower the surface work function. A schematic energy band diagram of the photocathode without an applied bias voltage is shown in Fig.…”

“…The procedure was essentially the same as that described in detail in the literature. 13) The photocathode spectral response characteristics were measured using a monochromator that was calibrated by a method in which it was combined with a thermopile and a previously calibrated germanium pin photodiode.…”