Photoelectric transient process in Si1-xGex/Si superlattices

The photoelectric transient process of a 99 period Si0.823Ge0.177 (17 Angst rom)/Si(24 Angstrom) superlattice (SL) was investigated by the photocurrent decay (PCD) method Decay lifetimes of electrons and holes in SL and Si cap ping layers are extracted from the transient intensity and polarity of the PCD signal. The temperature and bias dependences of lifetime exhibit the th ermal activation of heavy holes, the dissociation of free excitons and the thermal activations of shallow and deep levels. The heavy holes hop in and out of the well at low temperature and weak electric field, while they jump over the well region in a strong electric field or at high temperature. Li fetimes of electrons and holes are nearly the same in the Si capping layer, while the lifetime of holes is about one order of magnitude longer than th at of electrons in the SL, mainly due to the quantum confinement of holes i n the SL region.