Manipulation of Ge quantum dot ordering in alumina matrix by deposition conditions

We present an investigation of ordering and PL properties of Ge QDs in an alumina matrix formed by magnetron-sputtering deposition of (Ge+Al2O3)/Al2O3 multilayers. The self-assembly process occurs during the deposition and results with the formation of three-dimensional quantum dots lattices. We investigate the dependencies of the size and ordering properties on the deposition temperature, rotation of the substrate holder and direction of the incoming flux of Ge during the deposition process. The results of the investigation show that tuning the deposition temperature enables manipulation with QD sizes and their mutual distances. We show that the ordering of QDs obtained by deposition on fixed substrate holder leads to the formation of a quantum dot crystal, while the rotation of substrate holder leads to randomly rotated domains with regular ordering. The observed phenomenon is explained by a combination of the surface morphology effect on the nucleation positions of Ge quantum dots with a lateral inhomogeneity of the ad-atom flux. In addition, we show that the resulting quantum-dot lattices have size-dependent PL properties.