Subband resonance of electrons on Si(110)

Infrared resonant absorption from electron subbands on $n$-type Si(110) is studied for surface densities $N_s$ up to 1.2 × ${10}^{13}$ ${\mathrm{cm}}^{-2\mathrm{}}$. The 0→1 transition is observed in the perpendicular and, provided that the polarization is along the [110] axis in the surface, in the parallel-excitation modes. A distinct splitting on the order of 30% in $N_s$ is found for the two modes. It results from the absence of the depolarization shift (i.e., $\alpha =0\mathrm{}$) in parallel excitation. The comparison with a calculated subband splitting permits the determination of the exciton energy. The resonance shifts rapidly to higher energy with rising temperature in the range 4.2-200 K.