Electronic structure of amorphous semiconductor heterojunctions by photoemission and photoabsorption spectroscopy

Abstract

Heterojunctions of a‐Si: H/a‐Si1−x C x : H and a‐Si: H/a‐SiN x : H, deposited in situ by RF plasma CVD, were investigated by photoemission and photoabsorption using synchrotron radiation. The valence band maximum of a‐Si:H coincides with that of a‐Si x C 1−x : H and it is 1.4±0.2 eV above the VBM of a‐SiN x : H. As the a‐Si: H layer thickness decreases from 800Å to 5Å, the energy bandgap, determined from the difference between the L 2,3 edge, the Si‐2p binding energy and VBM, becomes progressively smaller than the optical bandgap. This suggests that excitonic effects on the L 2,3 edge are enhanced as the dimensionality is reduced from 3D to 2D.