Charge-transfer-doping-modulated amorphous semiconductor multilayer films

Abstract

Charge-transfer doping of hydrogenated amorphous silicon (a-Si:H) by amorphous insulators is demonstrated in multilayer films. Three different kinds of amorphous insulators, silicon nitride (a-SiN_x, silicon oxide (a-SiO_x and silicon oxynitride (a-SiO_xN_y) are tested. Plasma-deposited a-SiN_x is positively charged and acts as a donor with respect to 300 Å thick a-Si: H layers whereas plasma-oxidized a-SiO_x becomes negatively charged. The position of the Fermi level can be controlled by changing the composition of a-SiO_xN_y in a-Si: H/a-SiO_xN_y multilayer films at a constant a-Si: H sublayer thickness. Doping-modulated multilayer films of the form a-Si: H/a-SiN_x/a-Si: H/a-SiO_x exhibit only a light-induced conductance decrease due to the Staebler-Wronski effect but not the persistent excess conductivity that was observed in conventional doping modulated a-Si: H. This suggests that not only internal fields but also special defect states associated with dopant atoms are necessary for producing the light-induced excess conductivity.