(662e) Design of Semiconductor Surface Pits for Fabrication of Regular Arrays of Quantum Dots and Nanorings

Nanostructures such as quantum dots and nanorings exhibit outstanding properties that enable a broad range of applications in electronic devices due to the unique nature of electronic confinement in such nano-scale structures. Recent experimental studies have demonstrated self-assembly of ordered patterns of such nanostructures during epitaxial growth of thin films on pit-patterned substrate surfaces for a variety of film-substrate material systems. However, systematic theoretical and computational studies that can be used for optimal design of such pit-patterned substrates are very limited.

Here, we report a comprehensive computational study on the formation of ordered patterns of complex nanostructures consisting of quantum dots and nanorings on surfaces of coherently strained thin films grown epitaxially on pit-patterned substrates. Our analysis is based on self-consistent dynamical simulations according to a film surface evolution model that has been validated experimentally by comparison of its predictions with experimental observations on Ge films grown on Si pit-patterned substrates. We discuss the design of patterns of two pit geometries, namely, inverted truncated conical pits and pyramidal pits, and the effects on the resulting film surface nanopattern of varying the geometrical design parameters including film thickness, pit-pattern period, pit depth, pit opening size, and pit wall inclination. In the case of conical pits, we show that varying the pit opening diameter and the pit wall slope leads to formation of complex nanostructures inside the pits of a regular pit pattern on the film surface, which include quantum dots, as well as single nanorings and multiple concentric nanorings that may or may not surround a central quantum dot inside each pit. In the case of pyramidal pits, we find that varying the pit opening length and width and the pit wall inclination can lead to formation of nanostructures that include equi-spaced smaller pits or rectangular arrays of multiple quantum dots. Our simulation results for conical and pyramidal pit geometries are supported by linear and non-linear stability theories, respectively, which explain the film surface nanopattern formation as the outcome of a Stranski-Krastanow instability in the former case and of a nonlinear tip-splitting instability in the latter case. Our simulation predictions demonstrate that the ordered nanostructure patterns forming on the film surface can be controlled precisely by tuning the geometrical parameters of the pits on the pit-patterned substrate.

Our findings have important implications for designing optimal semiconductor surface patterns toward enabling future nanofabrication technologies. Our study also sets the stage for designing systematic experimental protocols for precise control of the shape and dimensions of complex nanoring and quantum dot structures arranged in ordered patterns on surfaces of epitaxially grown coherently strained semiconductor thin films.