Persistent Photoconductance Research Articles

Towards understanding persistent photoconductance in doping modulated amorphous silicon

Abstract We present a simple model to explain the origin of the persistent photoconductance (PPC) in p–n–p–n multilayers made of hydrogenated amorphous silicon: brief light exposures create metastable Staebler-Wronski defects in the p-type material, making it more intrinsic. This in turn pushes the Fermi level of the whole multilayer closer to the conduction band, thus causing the observed metastable increase of the electron dominated coplanar conductance of the multilayer. Much longer light exposures are needed to shift the Fermi level towards midgap due to Staebler-Wronski defects in the n-type layers, leading to a consequent decrease in the PPC effect. In support of our model we present experimental results on the creation rate and annealing kinetics of the light-induced metastable conductance changes in a multilayer and in p-type and n-type single layers.

Photo-induced and bias induced metastable states in the transverse conduction of PNPN doping-modulated a-Si:H superlattices

We report here large metastable changes in the conductance G(V) perpendicular to the layers of doping-modulated hydrogenated amorphous silicon (a-Si : H). A high or a low G(V) state is obtained with zero or a large bias applied while cooling from 160°C. A large persistent excess conductance (persistent photoconductance) is found after a brief illumination. This effect decreases with increasing bias applied during or after illumination.

Persistent photo-conductance and photoquenching of selectively doped Al0.3Ga0.7As GaAs/heterojunctions

The dependence on photon energy of the persistent photoconductivity (PPC) in selectively doped high mobility Al0.3Ga0.7As—GaAs heterostructures has been measured at temperatures below 80 K. A decrease in conductivity due to light exposure at one wavelength after exposure to light at another wavelength — photo-quenching — is also found. It is concluded that deep centers in GaAs and AlGaAs other than the DX center in AlGaAs are mainly responsible for PPC.