Temperature dependence of the electron intersubband resonance on (100) Si surfaces

Abstract

The dependence of the electron intersubband resonance on temperature has been studied between 4.2 and 130 K for photon energies 10.45, 15.81, and 44.32 meV. At the highest energy, distinct transitions from the ground state to each of the next three higher-lying levels (i.e., the 0→1, 0→2, 0→3 resonances) are observed. With rising temperature, the lines originating from the 0 ground-state subband shift and diminish in amplitude. The effect is attributed to thermal population of the higher-lying levels, in particular the 0′ subband of the fourfold degenerate valleys in the Si (100) surface. Firsthand evidence for the population of this level, and the existence of two distinct types of electrons at finite temperature, comes from the identification of a new resonance (i.e., the 0′→1′ transition) which grows with increasing temperature.