Space-charge spectroscopy of self-assembled Ge-rich dots on Si grown by MBE

The results of deep-level transient spectroscopy and admittance measurements of self-assembled Ge-rich dots are presented. The investigated quantum well (QW) Ge-rich layers in silicon consist of a thin-wetting QW layer with a width of 4-4.5 monolayers and three-dimensional dots (islands), with heights of about 6-8.5 nm and lateral dimensions of about 190-250 nm. Good agreement was observed with photoluminescence data. An enhancement of the lateral hole transport between the islands via the wetting layer due to thermally activated tunneling was observed. This effect is explained by a strong lateral electric field, which is induced by Coulomb charge of confined holes in the disc-shaped islands.