Figure 1: DFT results on SiO2 modulation doping with Al acceptors.
From: Modulation Doping of Silicon using Aluminium-induced Acceptor States in Silicon Dioxide
(a,b) Si10 nanocrystal (cyan) in three ML SiO2 (O is red, Si grey, H white) with Al atom (yellow) replacing Si in outermost SiO2 shell, showing β-HOMO (a) and β-LUMO (b) as iso-density plots of 4 × 10−4 e/cubic Bohr radius. (c) Electronic DOS (blue, red) of that approximant (energy scale refers to vacuum level Evac). DOS for pure SiO2 embedding (cyan, orange) is shown for comparison along with the HOMO and LUMO of a 1.9 nm Si nanocrystal fully terminated with OH groups22. The two possible MO spin orientations are noted by α and β due to unpaired electron configuration caused by the acceptor (doublet). (d) Band structures showing the principle of direct modulation doping for a Si nanocrystal (NC) in SiO2 and (e) for Si bulk terminated with SiO2:Al layer. Occupation of electronic states are described by chemical potential μ and Fermi level EF, respectively.
