Photoluminescence study of the 2D-3D growth mode changeover for different Ge/Si island phases

We report on a phase transition of Ge/Si islands grown by molecular beam ep itaxy as a function of growth temperature T-s and its impact on the photolu minescence properties. At T-s = 600 degrees C islands exhibit large 'dome-l ike' sizes and small areal densities. Reducing the growth temperature by a mere 20 degrees C reveals a different island phase which consists of much s maller pyramidal-like islands with an increased sheet density. Photolumines cence experiments show that for T-s = 600 degrees C both the wetting layer and the island related energy transitions are resolved. For the lower growt h temperature the wetting layer related photoluminescence vanishes during t he course of island formation.