Study of Barium Adsorption on Germanium by Field‐Emission Microscopy

The change in work function of barium‐covered p‐ and n‐type germanium emitters with the degree of coverage θ is investigated by FEM. The curve of work function φ against deposition time is similar to that for barium adsorption on metals. The work functions of clean field‐desorbed surfaces of p‐ and n‐type emitters are determined from the Fowler‐Nordheim slopes with respect to that for barium‐covered surfaces, assuming that the work function of the latter for θ > 1 is φBa = 2.5 eV. The work functions are φp = (4.90 ± 0.05)eV and φn = (4.43 ± 0.05) eV for φp = 3.7 Ωcm and Qn = 2.5 ωmcm, respectively. The difference in the observed work functions compares well with the difference of the Fermi level position. Metallic‐like properties of barium on germanium are observed at coverages θ much less than a monolayer (θ = 0.007).