Magnetic counterpart of persistent photoconductivity in narrow-gap semiconductors

At low temperatures, some ionic. covalent and mixed bonding compounds, as w ell as semiconducting heterostructures and quantum wells exhibit persistent photoconductivity. This term is used to describe the striking phenomenon i n which the conductivity of these compounds and/or structures is observed t o be greatly enhanced by visible or infrared illumination and the low resis tance state is maintained for a long time after switching off the illuminat ion. To describe this effect fit variously doped ionic-covalent semiconduct ors. models of repulsive barriers for both electron emission and capture we re introduced based primarily on the assumption of dopants displacement fit the host's crystal lattice. Here we report on the magnetic counterpart of this phenomenon. which however does not exactly meet the expectations based on transport measurements. It was found that the magnetic response. of A(I V)B(VI) narrow-gap semiconductors doped with C-III impurities possesses fea tures of both relaxation phenomena and light-induced phase transition. Expo sure of PbTe:Ga, PbTe:In and Pb0.75Sn0.25Te:In single crystals to white-lig ht illumination at low temperatures resulted initially in an increase of th e diamagnetic response and then in the appearance of a sharp paramagnetic p eak upon heating.