INFLUENCE OF MATERIAL SYNTHESIS AND DOPING ON THE TRANSPORT-PROPERTIES OF WSE2 SINGLE-CRYSTALS GROWN BY SELENIUM TRANSPORT

Resistivity and Hall effect measurements of WSe2 single crystals grown with excess selenium as transport agent in chemical vapor transport a re presented. The electronic properties are shown to depend strongly o n the materials selected for synthesizing polycrystalline powder used in the crystal growth procedure. Compensated high-resistivity samples of p-type doping were obtained with room-temperature carrier concentra tions of p approximate to 10(12) cm(-3) and activation energies of E-A = 450 meV. Changing the starting material resulted in low-resistivity p-type samples with p approximate to 10(17) cm(-3) and E-A approximat e to 80 meV. Vanadium doping leads to degenerate p-type samples with p approximate to 10(19) cm(-3). Copper doping changes high resistivity material to n-type conductivity. No significant changes of transport p roperties are observed for doping with Au, Ni,Mo, Cr, and Fe. Evidence is presented that the effective mass of holes in WSe2 is m(h) = 0.3m( 0).