Electronic Structure of Realistically Extended Atomistically Resolved Disordered Si:P δ-doped Layers
Date of this Version11-14-2011
Phys. Rev. B 84, 205309 (2011)
The emergence of scanning tunneling microscope (STM) lithography and low temperature molecular beam epitaxy (MBE) opens the possibility of creating scalable donor based quantum computing architectures. In particular, atomically precise Si:P monolayer structures (δ-doped layers) serve as crucial contact regions and in-plane gates in single impurity devices. In this paper we study highly confined δ-doped layers to explain the disorder in the P dopant placements in realistically extended systems. The band structure is computed using the tight-binding formalism and charge-potential self-consistency. The exchange-correlation corrected impurity potential pulls down subbands below the silicon valley minima to create impurity bands. Our methodology is benchmarked and validated against other theoretical methods for small ordered systems. The doping density is shown to linearly control the impurity bands. Disorder within the Si:P δ-doped layer is examined using an extended domain to describe the effects of experimentally unavoidable randomness through explicitly disordered dopant placement. Disorder in the δ-doped layer breaks the symmetry in the supercell and creates band splitting in every subband. Vertical segregation of dopants is shown to dramatically reduce valley splitting (VS). Such VS can be used as a measure of ideality of the fabricated Si:P δ-doped layer. Although the resulting disorder induces density of states fluctuations, this theoretical analysis shows that δ-doped layers can serve as quasimetallic 2D electron sources even in the presence of strong nonidealities.