Intersubband spectroscopy by photoconductivity and absorption in inversion layers onp−Si(100)

Subband spectroscopy in an inversion layer on $p-\mathrm{Si}\mathrm{}\left(100\right)\mathrm{}$ is done simultaneously in photoconductivity and absorption. The resonances observed are investigated in their dependence on inversion electron density $N_s$ and depletion charge $N_{\mathrm{dep}}$ and are interpreted as transitions from the ground subband to higher subbands of the two valleys with heavy mass perpendicular to the surface. Absorption and photoconductivity give identical resonance positions and similar lineshape. The dependence of the subband splitting on $N_s$ and $N_{\mathrm{dep}}$ is found to agree with the measurements of Kneschaurek et al. and the most recent theory by Ando. Agreement with the photoconductivity results of Wheeler and Goldberg and the hot-electron-induced emission experiment of Gornik and Tsui can only be achieved if the latter results are assumed to correspond to a much lower $N_{\mathrm{dep}}$ than derived from the substrate resistivity at 300 K. In contrast to the results of Wheeler and Goldberg the amplitude of the photoconductivity signal exhibits a strong temperature dependence between 1.7 and 6 K.