[′neg·əd·iv i′lek‚trän ə′fin·əd·ē mə‚tir·ē·əl] (electronics) A material, such as gallium phosphide, whose surface has been treated with a substance, such as cesium, so that the surface barrier is reduced, band-bending occurs so that the top of the conduction band lies above the vacuum level, and the electron affinity of the substance in negative. Abbreviated NEA material.