Abstract

Unlike direct band gap materials such as GaAs, which exhibit very sharp and strong absorption at the band edge, indirect gap crystalline silicon has relatively weak band edge absorption and hence weak band edge nonlinearities[1]. Even hydrogenated amorphous silicon (a-Si:H) with its quasi-direct bandgap shows only moderate electro-optic modulation at its nominally 1.7 eV band edge[2, 3] due to disorder-induced tail states. In addition, both a-Si:H and c-Si are centrosymmetric materials so that there are no χ⁽²⁾ optical nonlinearities.

© 1995 Optical Society of America