Electronic structure and properties of Cu2-xS thin films: Dependence of phase structures and free-hole concentrations

摘要

Cu2-xS has received increasing attentions in recent years, owing to its promising applications in a broad range of optoelectmnic devices. However, the phase structures and the electronic structures of Cu2-xS with varying Cu stoichiometries are surprisingly complex, and consensus on these aspects are still lacking. In this work, p-type polycrystalline Cu2-xS thin films with different phase structures and a wide range of free-hole concentrations N-Hall (10(19 )similar to 10(22) cm(-3)) were grown by controlling the Cu stoichiometries. We comprehensively studied the correlation of electronic structures and optoelectrical properties of Cu2-xS thin films with their phase structures and N-Hall. With increasing N-Hall of Cu2-xS with different phase structures, it is observed that i) the hole mobility mu reduces from similar to 6 to similar to 1 cm(2) V-1 s(-1) ; ii) the plasma energy E-p increases from similar to 0.3 to 1.2 eV; iii) the high-frequency dielectric constant epsilon(infinity) decreases linearly from similar to 10 to similar to 2.5; iv) the hole effective mass m(h)* increases from similar to 0.25 to 3.7 m(0); v) the direct optical bandgap E-G(Opt) slightly increases from similar to 1.9 to similar to 2.45 eV. Our results also reveal that the surface Fermi level of these Cu2-xS thin films is located above the corresponding valence band maximum, likely due to the presence of surface oxidation and/or the surface defects.

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