Si/CaF² Superlattices. A Direct Gap Structure Due to Interface State Coupling

Abstract

One promising approach for the development of silicon-based light-emitting devices is the epitaxial growth of Si nanostructures. In this context, the lattice matched system CaF,/Si/CaF, as prototype of a well controlled and ordered Si-based system with known microscopic structure is proposed. For this system, a new mechanism is found leading to a direct band gap based on the coupling of interface states in very thin Si layers.

Disorder Effects on the Gap of Thin Si Nanocrystalline Films

“…This choice of parameters for the H and the Si±H interactions is in good agreement with DFT-LDA determination of Hamiltonian and overlap matrix elements [7] and also reproduces accurately the valence band and low conduction band energies (near the gap) of monocrystalline Si films but results in a too large H density of states within the conduction band (2 or 3 eV from the bottom of the conduction band) compared to abinitio calculations [9].…”

“…[7]. The Si±H coefficients are chosen to reproduce ab-initio LMTO band structure calculations of hydrogenated monocrystalline Si layers [9]. We also assume the Si±H interaction to be inversely proportional to the square of the inter-atomic distance d ± ±2 [8] times an exponential decrease f = exp [± ±(d ± ± 1.48)/2.48].…”