Date of Award

Spring 1999

Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical & Computer Engineering

Committee Director

Hani E. Elsayed-Ali

Committee Member

Sacharia Albin

Committee Member

Ravindra Joshi

Committee Member

Kenneth Brown


Fabrication of high quantum efficiency, long lifetime negative electron affinity photocathodes is important for applications such as photomultipliers, image intensifiers, electron beam lithography, electron microscopy, and polarized electron sources. The surface cleanliness of the III-V semiconductor photocathode is crucial in obtaining high photosensitivity.

GaAs(100) and InP(100) photocathodes are prepared by atomic hydrogen cleaning. The cleaning effect on the photocathode performance is discussed. The surface degradation mechanisms which reduce the photocathode lifetime are presented. The photocathode surface cleanliness, structure, and morphology are studied using reflection high-energy electron diffraction (RHEED).

Quantum efficiencies of ∼14% and 8% are obtained for GaAs and InP, respectively, in response to 632.8 nm light after atomic hydrogen cleaning. Longer photoemission time is obtained under low accelerating voltage, low light and photocurrent intensities, and continuous cesiation. RHEED patterns after atomic hydrogen cleaning show reconstructed, group V terminated surfaces suitable for negative electron affinity activation. The out-of-phase diffraction patterns after atomic hydrogen cleaning or reviving have higher intensities than those obtained after heat cleaning, indicating that the surfaces have less defects and contaminants.