Electronic and optical properties ofSi∕SiO2nanostructures. I. Electron-hole collective processes in singleSi∕SiO2quantum wells
Physical Review B
Photoluminescence measurements have been performed at low temperature on crystalline Si/ SiO 2 quantum wells as a function of thickness. Three distinct electron-hole ͑e-h͒ phases are clearly identified in these structures: the electron-hole liquid, the electron-hole plasma, and the free-exciton gas. It is shown that spatial confinement induced by the SiO 2 barriers modifies the thermodynamical equilibrium between these phases with respect to the bulk case by changing the steady state of the
... dy state of the carrier system and involving new transient states. In the low-thickness domain, the e-h recombination line blueshifts as a result of the effect of quantum confinement on the band-edge positions. Data are analyzed thanks to a model taking account of the new band-diagram parameters-effective mass, band degeneracy, anisotropy-and image charges in the dielectric barrier which modify the strength of Coulomb interactions between carriers in the Si well. Results interpreted in the frame of a simple coalescence model indicate that the two-dimensional electron-hole liquid forms a cloud of in-plane pancakes. Finally, an attempt is made here to compute the phase diagram of carriers in varying-thickness quantum wells by means of a spin-1 lattice-gas model and to predict the nature of the two-dimensional e-h collective state.