Coordinated and Simultaneous Formation of Paired Ge Quantum Dots by Thermal Oxidation of Designer Poly-SiGe Spacer Structures

We report a novel self-organized approach for the controllable placement of paired Ge quantum dots (QDs) along each sidewall edge of poly-Si ridges by simply thermally oxidizing spacer layers of poly-SiGe and Si₃N₄ that conformally encapsulate the poly-Si ridges. Additionally, controllable diameters ranging from 20-50 nm and precise location of paired Ge QDs are enabled by adjusting the thickness of poly-SiGe spacer layers in combination with specific processing conditions. These conditions include the subsequent lithographic patterning through direct etch-back for forming spacer stripes and spacer islands. The spacing between paired Ge QDs across the ridge is essentially determined by the width of the patterned poly-Si ridge. Inter-QD spacings along the sidewall of the poly-Si ridge are a consequence of heterogeneous nucleation and Ostwald Ripening.