Giant magnetoresistance of PbSnTe:In films in the space-charge-limited current regime: Angular features and effect of the surface

In the space-charge-limited current regime at $T = 4.2$ K, the magnetoresistance of PbSnTe:In/(111)BaF$_2$ films has been studied at various mutual orientation of the magnetic field $\mathbf{B}$ (up to 4 T), electric field $\mathbf{E}$ (up to $\sim$10$^3$ V/cm), and normal to the surface $\mathbf{n}$. At $\mathbf{ B}\parallel\mathbf{ n}$, the reduction of the current reaches a factor of $\sim$10$^5$, whereas at $\mathbf{ B}\parallel\mathbf{ E}$, the current increases by a factor of $\sim$10$^3$. The angular dependences of the magnetoresistance have been studied at the “rotation” of $\mathbf{B}$ in three different planes. The angular dependences of the magnetoresistance for the plane corresponding to the orientation $\mathbf{ B}\perp\mathbf{ E}$ exhibit local maxima near the orientations $\mathbf{ B}\perp\mathbf{ n}$, at which charge carriers are deflected by the magnetic field to one of the boundaries of the film. At the deviation to the free surface, the half-width of maxima is several degrees. At the deviation to the interface with the substrate, the half-width of maxima is about an order of magnitude larger and their amplitude is one or two orders of magnitude smaller. Possible mechanisms of giant positive and negative magnetoresistance, as well as the effect of the boundaries of the film on the angular dependences of the magnetoresistance, have been discussed.