Epitaxial growth, electronic properties, and photocathode applications of strained pseudomorphic InGaAsP/GaAs layers

The results of experimental and theoretical investigations directed toward the development of highly efficient sources of spin-polarized electrons are reported. The sources are based on heteroepitaxial elastically strained films of the quaternary InGaAsP solid solution grown by liquid-phase epitaxy on GaAs substrates. The InGaAsP films synthesized were 0.1-0.2 mum thick with the band gap being within the range of 1.4-1.9 eV and having elastic strains as high as 1%. This provided splitting of the valence band top by 40-60 meV and a degree of the spin polarization P of the electrons photoemitted as high as 80%. The films have a high quantum yield of photoemission Y upon activating to the negative electron affinity state due to the adsorption of Cs and O. Record values for the effective figure of merit (PY)-Y-2 are achieved. (C) 2001 MAIK "Nauka/Interperiodica".