Ι.- Proof-of-concept for graphite-like 2D-nanolattices
We will prove that although not existing in Nature, graphite-like 2D nanolattices of dielectrics and semiconductors can be engineered on suitable substrates. The center of focus will be to find ways to induce and stabilize sp2 hybridization in Si (and Ge) to obtain silicene and germanene with a 2D honeycomb lattice and investigate their properties in comparison to bulk Si (and Ge) and graphene.
Our first priority is to grow silicene and germanene on “friendly” substrates such as Silver or other metals. Subsequently, we will grow graphite-like 2D dielectrics (e.g. hexagonal AlN,) on metal substrates or silicon, which could primarily offer a template for silicene and germanene overgrowth and, at the same time, serve as gate insulators to ensure adequate charge and current control in the silicene layer.
II. - Opening and control of the energy gap
The existence of an energy gap in graphite-like lattices is highly desirable for digital logic and a number of other applications based on the expectation that the presence of a gap will allow a modulation of their electronic properties by an external perturbation (electric field, temperature, light etc) as in an ordinary semiconductor.
Our main approach is to functionalize the 2D silicene “surface” by exposing it to suitable adsorbants which could weaken the -bonding opening a gap. We will apply atomic oxygen and ozone as the main adsorbant species, while exposure to controlled water vapor atmosphere of H plasma treatment will also be among our options.
III. - Demonstration of generic electric field effect devices
We will focus on generic 2D dielectric/silicene (germanene)/2D dielectric device structures, which on one hand allow for an estimation of critical materials parameters (carrier concentration, conductivity and mobility) and on the other hand permit the investigation of the electric field effect in silicene and germanene. This will allow for a first comparison with present day electronic devices which are largely based on the same effect (e.g field effect transistors-FETs) and helps identifying strengths and weaknesses of the proposed new graphite-like layered materials compared to ordinary bulk semiconductors and dielectrics.
A number of other effects and critical parameters such as carrier trapping and losses at defects are totally unexplored and they will be investigated in detail using advanced characterization techniques already proven from semiconductor MOS research.
IV. - Si(Ge) engineered anisotropic superlattices
The aim here is to generate anisotropy in the electronic properties of regularly sp3-hybridized ultrathin Si and Ge. This can be implemented by inserting monolayer(s)-thick non-semiconducting layers such as N, O or C to artificially break the Si (or Ge) lattice periodicity along the vertical growth direction. In such a case, the band structure and the density of states could be strongly modified, reducing in-plane effective mass, while inhibiting the transport perpendicular to the layers. This could reduce both the gate leakage and the carrier scattering, thus maintaining high mobility at low equivalent oxide thickness (EOT). The work here will complement our mainstream effort on 2D sp2-hybridized highly anisotropic lattices increasing our chances to obtain device structures with potential superior electronic properties compared to standard Si devices.