Photoemissive, Photoconductive, and Optical Absorption Studies of Alkali-Antimony Compounds

By means of absorption and photoconductivity measurements, the following band gaps were found: Na₃Sb---1.1 ev; K₃Sb---1.1 ev; Rb₃Sb---1.0 ev; Cs₃Sb---1.6 ev; and (NaK)₃Sb---1.0 ev. A model has been derived for the photoemission from these materials which fits the three last materials listed above in addition to the (NaK)₃Sb with surface layers of Cs or Rb added. The electron affinities found from the photoemissive data using this model were as follows: Rb₃Sb---1.2 ev; Cs₃Sb---0.45 ev; (NaK)₃Sb---1.0 ev; [Rb](NaK)₃Sb---0.70 ev; and [Cs](NaK)₃Sb---0.55 ev. The electron affinity of K₃Sb was estimated to be between 1.1 and 1.8 ev and that of Na₃Sb to be between 2.0 and 2.4 ev. By means of the temperature dependence of the photoemission, Rb₃Sb, Cs₃Sb, and the multi-alkali materials were found to have p-type conductivity; whereas K₃Sb and Na₃Sb were found to have n-type conductivity.