WORK FUNCTION AND STRUCTURAL STUDIES OF ALKALI-COVERED SEMICONDUCTORS

Work function and LEED measurements have been made on clean and alkali-covered Ge and Si surfaces. Aluminosilicate ion sources have been used to deposit accurately measurable quantities of Na, K, and Cs ions on surfaces normal to the Ge(111), Ge(100), Si(111) and Si(100) crystal directions. The resulting work function versus alkali metal coverage curves, when plotted on semi-log paper, consist of nearly-straight line segments with distinct breaks. The coverages at which the breaks occur are consistent with the clean surface structures determined for each surface by LEED observations. The breaks occur at multiples of 1 8 monolayerfor the Ge(111) surface which has a 2 × 8 surface unit mesh and at multiples of 1 7 monolayer for the Si (111) surface which has a 7 × 7 surface unit mesh. The data make an excellent fit with a model which uses the Topping calculation for depolarization and a different dipole moment for each line segment of the curve. This model implies migration of the alkali metal to different preferred binding sites during each region of coverage. © 1969.