MOVPE growth and transport characterization of Bi2−xSbxTe3−ySey films

Abstract

We present a first study of films of the quaternary Bi2−xSbxTe3−ySey solid solutions on (0001) sapphire substrates grown by atmospheric pressure MOVPE. Trimethylbismuth, trimethylantimony, diisopropylselenide and diethyltelluride were used as precursors. To passivate the free bonds of the substrate and to improve the epitaxy, a thin (15 nm) ZnTe buffer layer was first grown. EDX analysis of the films grown at a temperature of 445 °C and about 10-fold excess of chalcogen in the vapor phase indicates on their compliance with V2VI3 stoichiometry. AFM and SEM investigations showed that at the initial stage of deposition the Stranski-Krastanov growth mode is dominant. Complete coalescence of nanoislands occurs at a thickness about 60 nm and further film formation is in the 2D layer-by-layer growth mode. A high mole fraction of antimony in the vapor phase leads to bad crystalline quality of the films and even to their discontinuity. Transport properties of the Bi2−xSbxTe3−ySey films were evaluated using Van der Pauw Hall effect measurements in the range of temperatures of 10–300 K. Some films are always n- or p-type; in other samples the change of conductivity from p- to n-type was observed when the temperature decreases.