Growth and photoluminescence of self-assembled islands obtained during the deposition of Ge on a strained SiGe layer

The growth and photoluminescence of Ge(Si) self-assembled islands on strained Si1−xGex layers (0 < x < 20%) has been investigated. Both island size and density increase when the Ge content in the predeposited Si1−xGex alloy increases. The increased island density is associated with an enhanced surface roughness after SiGe deposition. The increased island size is attributed to enhanced Si intermixing and to a wetting layer thickness reduction. The latter is caused by accumulation of elastic strain energy in the SiGe layer. The increase in both island size and density leads to a strong interaction between neighboring islands. The island-island interaction results in island self-ordering, which is analyzed using a surface autocorrelation function. The lower Ge content in the islands accounts for the observed blueshift of the island related photoluminescence signal. We observe a room temperature photoluminescence signal for Ge islands grown on a predeposited SiGe alloy which is higher than for Ge islands grown on Si(0 0 1). This result is explained by an increased island density, which provides an efficient way to capture charge carriers in the islands.