Improvement in photocurrent with n-type niobium- and rhenium-doped molybdenum and tungsten diselenide single crystals

<b>The structure of niobium-doped MoSe2 and WSe2</b>

“…Niobium (|Kr| 4d 4 5s 1 ) exists in its compounds in oxidation states: Nb 3+ (4d 2 ), Nb 4+ (4d 1 ) and Nb 5+ (4d 0 ). We showed previously [9] that the insertion of niobium into the network of MSe 2 creates deep donor levels, which then enhance the n-type character of the single crystals obtained with a metallic character that increases with doping. It was suggested that the donor level requirement is that this metal exists in the network of MoSe 2 as Nb 5+ .…”

“…In previous work [9] we examined ways to increase the photoconductivity of MSe 2 transition metal n-type dichalcogenides. Niobium-and rhenium-doped single crystals were obtained by chemical vapour transport from a polycrystalline 1 % metal-doped solid solution, using as transport agent iodine in the case of MoSe 2 , and SeCl 4 in the case of WSe 2 [Throughout this paper % composition denotes atomic %].…”

A Van Der Waals Homojunction: Ideal p–n Diode Behavior in MoSe2

“…One fundamental question is whether the elemental doping, which has been successful for controlling carrier types in bulk material, works for 2D layered materials having weak vdW interaction. Historically well‐known elemental doping method has been also adopted in bulk TMdCs . For example, Nb (five valance electrons) or Re (seven valance electrons) has been used for a substitutional p‐type or n‐type dopant to replace the cation such as Mo or W with six valance electrons, where Nb has no miscibility gap for Mo alloys .…”

“…Historically well‐known elemental doping method has been also adopted in bulk TMdCs . For example, Nb (five valance electrons) or Re (seven valance electrons) has been used for a substitutional p‐type or n‐type dopant to replace the cation such as Mo or W with six valance electrons, where Nb has no miscibility gap for Mo alloys . Recently, for 2D layered materials, this concept is expected by the theoretical calculation and was also demonstrated for MoS 2 .…”

The growth and thermodynamical feasibility of tungsten diselenide single crystals using chemical vapour transport technique

“…The transition metal disulphides and diselenides have attracted considerable attention during the past few years (Legma et al 1991;Patel 1992;Agarwal et a11993;Gallagher et al 1994). These MX2 (M = transition metal; X = chalcogen) compounds are formed by a layer of transition metal atoms between two layers of sulphur or selenium atoms.…”