Nonequilibrium Rock-Salt-Type Pb-Doped SnSe with High Carrier Mobilities ≈ 300 cm2/(Vs)

We synthesized nonequilibrium cubic rock-salt (RS)-type (Sn,Pb)Se and investigated their optoelectronic properties with the expectation that the RS-type structure would exhibit better carrier transport properties than the equilibrium GeS-type layered crystal structure in SnSe because the RS-type structure has the three-dimensional network of (PbSe6) octahedra, while the GeS-type structure has the two-dimensional network of (SnSe3), leading to larger band dispersions and smaller carrier effective masses. To stabilize the nonequilibrium phase, epitaxial thin films were grown by a unique method, a reactive solid-phase epitaxy with a thin RS-type PbSe epitaxial template layer. Additionally, a rapid quenching process from 600 degrees C to room temperature was also effective for stabilizing the nonequilibrium RS-type (Sn,Pb)Se epitaxial films. We succeeded in controlling Pb concentration continuously from 0 to 100% in the (Sn,Pb)Se solid-solution films. The minimum Pb concentration to stabilize the RS-type SnSe was extended from the previously reported value of 63% to 50%. A band gap bowing effect was observed with the smallest estimated band gap of similar to 0.14 eV for the RS-type (Sn0.35Pb0.65)Se. The GeS-type to RS-type structural change increased hole mobility drastically from 60 for SnSe to 290 cm(2)/(Vs) for 58% Pb-doped RS-type (Sn,Pb)Se film as expected. It was found that p-type to n-type conversion occurs by further higher Pb concentrations >= 61%, and the highest electron mobility of 340 cm(2)/(Vs) was observed.