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

By means of absorption and photoconductivity measurements, the following band gaps were found: ${\mathrm{Na}}_{3}$Sb---1.1 ev; ${\mathrm{K}}_{3}$Sb---1.1 ev; ${\mathrm{Rb}}_{3}$Sb---1.0 ev; ${\mathrm{Cs}}_{3}$Sb---1.6 ev; and ${(\mathrm{NaK})}_{3}$Sb---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 ${(\mathrm{NaK})}_{3}$Sb with surface layers of Cs or Rb added. The electron affinities found from the photoemissive data using this model were as follows: ${\mathrm{Rb}}_{3}$Sb---1.2 ev; ${\mathrm{Cs}}_{3}$Sb---0.45 ev; ${(\mathrm{NaK})}_{3}$Sb---1.0 ev; [Rb]${(\mathrm{NaK})}_{3}$Sb---0.70 ev; and [Cs]${(\mathrm{NaK})}_{3}$Sb---0.55 ev. The electron affinity of ${\mathrm{K}}_{3}$Sb was estimated to be between 1.1 and 1.8 ev and that of ${\mathrm{Na}}_{3}$Sb to be between 2.0 and 2.4 ev. By means of the temperature dependence of the photoemission, ${\mathrm{Rb}}_{3}$Sb, ${\mathrm{Cs}}_{3}$Sb, and the multi-alkali materials were found to have $p$-type conductivity; whereas ${\mathrm{K}}_{3}$Sb and ${\mathrm{Na}}_{3}$Sb were found to have $n$-type conductivity.