Highly uniform arrays of epitaxial Ge quantum dots with interdot spacing of 50 nm

Abstract

Periodic, highly uniform arrays of dome-like Ge quantum dots (QDs) with 50 nm interdot pitch have been achieved on Si (001). The Si surface was patterned using ultra-low-dose focused ion beam and defect-selective etching, resulting in a continuously height-modulated, "egg-carton" morphology. The directed self-assembly process is robust, occurring across a range of ion doses, growth temperatures, and deposition rates. By selectively etching off the Ge dots to reveal the underlying Si surface just prior to Ge growth, we showed that Ge QDs preferentially formed on crowns (regions of negative curvature) rather than pits (regions of positive curvature) as is mostly seen in the literature. The width of the QD size distribution mimics that of the underlying substrate pattern, indicative of a complete lack of coarsening during the Ge growth, despite the small length scales, and extensive mass transport leading to QD formation.

Optical properties of individual site-controlled Ge quantum dots

“…[1][2][3][4] A main motivation for studying the optical properties of this material system is the prospect of efficient light emitters and single photon sources in the near infrared spectral range for monolithic integration into a silicon device platform. 5 Recent progress in site-controlled growth of SiGe QDs on pre-patterned Si(001) substrates, [6][7][8][9][10] and their commensurable embedding into photonic crystal slabs 11 has opened a unique route toward deterministic positioning of individual SiGe QDs in photonic crystal resonators. Yet, optical studies were mainly performed on ensembles of SiGe QDs, which cause broadening of the photoluminescence (PL) lines due to variations in QD size [12][13][14][15][16] and local composition.…”

Structural properties of templated Ge quantum dot arrays: impact of growth and pre-pattern parameters

“…For the pitches below 300 nm only few reports are found. Realization of QD arrays was reported with pre-pattern pitches of 50 and 35 nm [31,32]. These studies, however, concentrate on a single pitch and do not allow to predict the required changes of MBE growth parameters for other pitches, pit diameters and different QD morphologies.…”

Directed Self-Assembly of Ge Quantum Dots Using Focused Si2+ Ion Beam Patterning

“…Low-dose templating 10 – 14 is beneficial for patterning quantum dot arrays on planar surfaces because it does not significantly alter the substrate surface, leaving the substrate suitable for further processing. FIB-templated quantum dots have successfully been positioned within 100 nanometers of each another 8 , 13 , and recently, more complicated protocols have been attempted to reduce the separation between quantum dots even further 15 . The ultimate objective is to achieve precise control over the placement of quantum dots that also have well-defined physical structure, electronic structure, and doping.…”