Electronic and optical properties ofSi∕SiO2nanostructures. I. Electron-hole collective processes in singleSi∕SiO2quantum wells

N. Pauc, V. Calvo, J. Eymery, F. Fournel, N. Magnea
2005 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
more » ... ier 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.
doi:10.1103/physrevb.72.205324 fatcat:pencnugttrhb3be2uiaid346pq