Acceptor Modulation Doping of SiO_2 for Providing Holes to Si Quantum Dots

摘要

The thermodynamics of foreign atoms in nano crystals (NCs) shows that conventional doping is not feasible to a degree required for high quality devices. Modulation doping is used for III-V super lattices (SLs), with excellent results for majority carriers. Adopting modulation doping to Si NCs in a SiO_2 matrix is difficult. We investigated α-SiO_2 approximants by ab-initio methods. Conventional Si dopants fail to deliver shallow energy levels which can be occupied. Finding donors in SiO_2 in order to provide electrons for Si NCs is not possible due to the strong anionic nature of oxygen (O). However, scandium (Sc) works as an acceptor when replacing Si. The electronic nature of Sc results in a lowest unoccupied molecular orbital (LUMO) at an unusually high electron affinity (X). This LUMO can then be doubly occupied by accepting an electron from Si NCs. The doping approach does not depend on the NC material.