Ge films of thicknesses within the p-boundary layer thickness are precipitated under ultra high vacuum conditions, at 77°K. They are investigated either in the disordered state (before annealing at a higher temperature) or in the ordered state (after annealing). The electric resistance R and the photoelectric work function Φ are measured before and after the influence of known amounts of oxygen. R is plotted as a function of time and coverage n, Φ as a function of n. Small amounts of oxygen cause R to increase without changing Φ, large amounts result in a succeeding decrease of R and cause Φ to increase by 0.1 to 0.2 V. The results are discussed by means of a band model. At small coverages oxygen acts as an electron donator, at higher coverages as an electron acceptor.
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