GaAs photocathode cleaning by atomic hydrogen from a plasma source

Abstract

A clean GaAs surface is required in order to fabricate negative-electron-affinity photocathodes. Surface preparation is routinely performed by chemical cleaning and heating in ultra-high vacuum. These processes could damage the surface and produce photocathodes with low quantum efficiencies. Here an alternative technique which overcomes these problems, namely chemical cleaning and heating in ultra-high vacuum, is used. A helical resonator discharge produces hydrogen plasma which is used in a down-flow configuration to clean the GaAs(100) surface of a bulk crystal and strained layer GaAs prior to activation to negative electron affinity. Atomic hydrogen reacts with the oxides and hydrocarbons on the surface, forming volatile compounds. The photocathodes are prepared by depositing caesium onto the clean semiconductor surface. The photoemission current increases with surface cleaning. The reflection high-energy electron-diffraction pattern after atomic hydrogen cleaning reveals a clean 2 × 4 reconstructed GaAs(100) surface compared with a halo before cleaning.

Bias dependent inversion of tunneling magnetoresistance in Fe∕GaAs∕Fe tunnel junctions

“…Contaminations on a GaAs surface can thus be effectively removed. 11,12 We used an ion sputter gun under an angle of ~22° with an acceleration voltage of 1 kV for 30 min at RT. The hydrogen treatment does not attack the GaAs barrier.…”

Effects of ion bombardment on bulk GaAs photocathodes with different surface-cleavage planes

“…After verifying that each sample provided high QE at 532 nm, the NEA layer was removed. Then samples were implanted with hydrogen ions from an atomic hydrogen source, originally used to clean photocathodes [9,10], but used here as an ion source, The energy of the implanted ions was determined by the value of the negative bias applied to the photocathode (more details provided below). Samples were then heated and reactivated-i.e., chemicals were reapplied to the GaAs surface to recreate the NEA condition.…”

Atomic hydrogen-cleaned GaAs(100) negative electron affinity photocathode: Surface studies with reflection high-energy electron diffraction and quantum efficiency

“…14 Under atomic hydrogen irradiation, carbon is completely removed at 200°C, and the surface oxides are removed at 400°C. 18,19 In the present work, we study the morphology of the GaAs͑100͒ vicinal surface after atomic hydrogen cleaning. The incident electron beam hits the surface at near-grazing angle and is diffracted.…”