LETTER TO THE EDITOR: On electron confinement effects and the ultimate size reduction in semiconductor devices

Three-dimensional electron confinements cause a blue shift of the fundamental band gap and a size-induced metal-insulator transition. These quantum-size effects are expected in confinements with diameters up to the order of 10 and 100 nm at room temperature, in metals and semiconductors, respectively. The size effect can markedly be enhanced by an additional phonon confinement which is omnipresent in isolated sub-micrometre crystals. Confinement effects represent the limitation for the ultra-large-scale integration.