Grating-coupler-induced intersubband resonances in electron inversion layers of silicon

Resonant intersubband transitions in electron inversion layers on the three principal surfaces of Si have been studied with efficient grating couplers. For Si(111) and Si(110) both directly parallel excited and grating-coupler-induced depolarization-shifted resonances are observed and their dependence on the surface electric and depletion fields studied. For Si(100) intersubband resonances are investigated up to charge densities Nₛ=1.2×{}10¹³ cm^-2. At high densities transitions in the primed subband system are observed. Also for Si(100), there is evidence for parallel excited resonance transitions, which are strictly forbidden for vertical transitions ({Δ}k=0), but become allowed for grating-coupler-induced nonvertical transitions ({Δ}k{≠}0). On all three surfaces a strong interaction of the intersubband resonances with optical phonons in the adjacent SiO₂ layer is found.