We propose a novel method for the engineering of 1D nanostructure fabrication with no need of catalyst agents. The method is based on a lithography design of a pattern of channels onto a conveniently cleaved semiconductor surface. We believe that this method opens a range of possibilities for optoelectronic nanodevices with improved efficiencies.
We demonstrate by means of electronic structure calculations that when the channel diameter is sufficiently larger than the interstitial space, the resulting pillars constitute an ordered array of electronically independent, though mechanically interconnected nanowires. We also show that a controlled coupling of the nanowires can be achieved, as long as one is capable to tune, at fabrication time, the thickness of the interconnections, which are ultimately responsible of the efficiency of the quantum confinement. This method, being based on a top-down approach, would yield an ensemble of identical nanowires, grown along the same crystallographic orientation and with similar properties concerning length and diameter.
We study [1] different templates, where the channels are distributed according to a square or a hexagonal network, discussing the case of Si and GaAs. The hexagonal distribution of channels proved to offer the best confining properties. Calculations have been carried with the Siesta ab-initio package. For a Si substrate and holes in a square disposition, we observe that states remain in the wire section. However, after widening the interconnect, laterally propagating states appear. The dispersive behaviour is conclusively determined from the observation of the band width for the bands of interest.
We also present results for GaAs structures with less demanding (i.e. larger) feature sizes obtained with the Effective Bond Orbital Model. Structures with the same hole pitch can present both isolated nanowire and 2D superlattice behavior depending on the channel diameter.
The use of such structures could be easily extended to quantum well or superlattice substrates, e.g. GaAs/InGaAs or GaAs/GaAsP, leading to the fabrication of 1D heterostructures or quantum dots with potential applications as light emitting devices.
[1] R. Rurali, J. Suñe and X. Cartoixa, Appl. Phys. Lett., 90, 083118 (2007). |