Special Beam Physics Seminar

Tuesday, November 25, 2003, 9:30 AM
ARC Bldg. Room 231/233

Cu(In,Ga)(S,Se)2 Crystal Growth, Structure, and Properties

Angus Rockett
University of Illinois Champaign-Urbana

Proposals for a new electron/light-ion collider (ELIC) impose demanding requirements on the polarized electron source, namely high average current (mA) and high polarization (>80%). Lasers do not exist that can produce enough beam while using traditional strained-layer GaAs photocathodes (QE ~ 0.1%). New GaAs superlattice photocathodes have recently demonstrated higher yield (QE ~ 1%) but even these photocathodes necessitate laser R&D to meet ELIC beam requirements. Chalcopyrite photocathodes may offer the best means to meet ELIC beam requirements. These photocathodes promise yield as high as bulk GaAs (QE ~ 10%) and high polarization. Successful demonstration of these properties will greatly simplify drive laser requirements for new accelerator facilities like ELIC.

This talk will present an overview of issues related to the structure, properties, phase relationships, and methods of epitaxial crystal growth of Cu-chalcopyrite semiconductor materials. Other ternary chalcopyrite semiconductors such as Ag-based compounds generally follow similar behaviors to the extent that they have been studied. A review of the Cu-In-Se ternary phase diagram and other phase equilibria relevant to understanding the material properties will be described. Special emphasis will be placed on the crystallography, electronic structure, point defects in the material, and other issues related to obtaining a spin-polarized electron emitter. Surface energies, surface morphologies, and extended defects are considered and chemical changes near the surface are discussed.

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