Quantum-confinement effect in ultrathin Si layer of silicon-on-insulator substrate

We have studied the evolution of valence-band spectra during Si layer thinn ing in a silicon-on-insulator (SOI) substrate by X-ray photoelectron spectr oscopy (XPS) in order to observe the quantum-confinement effect in two-dime nsional Si. It was clearly observed that the valence-band maximum (VBM) shi fts towards higher binding energies with decreasing Si thickness (< similar to 10nm). The VBM shifts were ascribed to vertical confinement of heavy ho les in the quantum-well structure of a vacuum/single-crystalline Si/buried amorphous SiO2.