Polymorphic One-Dimensional (N₂H₄)₂ZnTe:  Soluble Precursors for the Formation of Hexagonal or Cubic Zinc Telluride

Abstract

Two hydrazine zinc(II) telluride polymorphs, (N2H4)2ZnTe, have been isolated, using ambient-temperature solution-based techniques, and the crystal structures determined: alpha-(N2H4)2ZnTe (1) [P21, a = 7.2157(4) Angstroms, b = 11.5439(6) Angstroms, c = 7.3909(4) Angstroms, beta = 101.296(1) degrees, Z = 4] and beta-(N2H4)2ZnTe (2) [Pn, a = 8.1301(5) Angstroms, b = 6.9580(5) Angstroms, c = 10.7380(7) Angstroms, beta = 91.703(1) degrees, Z = 4]. The zinc atoms in 1 and 2 are tetrahedrally bonded to two terminal hydrazine molecules and two bridging tellurium atoms, leading to the formation of extended one-dimensional (1-D) zinc telluride chains, with different chain conformations and packings distinguishing the two polymorphs. Thermal decomposition of (N2H4)2ZnTe first yields crystalline wurtzite (hexagonal) ZnTe at temperatures as low as 200 degrees C, followed by the more stable zinc blende (cubic) form at temperatures above 350 degrees C. The 1-D polymorphs are soluble in hydrazine and can be used as convenient precursors for the low-temperature solution processing of p-type ZnTe semiconducting films.

High‐Mobility p‐Type Transistor Based on a Spin‐Coated Metal Telluride Semiconductor

“…It has been proposed that Cu + mobility under applied electric field may even be used to establish intentional doping profiles in these materials. [23] In summary, the present solution-processed CuInTe 2 films further highlight the relatively broad applicability of hydrazine as a solvent for the preparation of metal-chalcogenide films, [1][2][3]9,10] including metal tellurides, and provide the highest mobilities to date for p-type spin-coated semiconductors (by approximately an order of magnitude). The CuInTe 2 study is also important since it provides an example of a metal-chalcogenide system that is not by itself significantly soluble in hydrazine.…”

“…[15][16][17] Given the relatively high reported bulk mobilities and potential for use in electronic and optoelectronic devices, the telluride-based chalcopyrite represents a natural choice for prospective deposition from hydrazine solutions. In contrast to previously studied solution-processed chalcogenide systems, including SnS 2 , SnSe 2 , In 2 Se 3 , Sb 2 S 3 , Sb 2 Se 3 , ZnTe, and Cu 2 S, [1,3,9,18] (Fig. 1, inset).…”

“…Recently, we demonstrated the deposition of p-type ZnTe films from a hydrazine-based solution. [9] However, initial results employing these telluride-based films in transistors did not yield high mobility, perhaps because of poor grain structure or deleterious surface states in the ultrathin films. Films of p-type CuInSe 2 have similarly been deposited from a hydrazine-based solution, although again the performance of the devices was not in the range of the previous n-type systems (< 1 cm 2 V -1 s -1 ).…”

Solution Processing of Chalcogenide Semiconductors via Dimensional Reduction

“…23). [43] In contrast to the crystalline sulfide and selenide precursors discussed earlier, which consist of metal chalcogenide anions separated by hydrazinium cations, in (N 2 H 4 ) 2 ZnTe, the structure is comprised of extended ZnTe chains with covalently coordinated neutral hydrazine molecules (two per Zn atom). Two distinct structures, a-(N 2 H 4 ) 2 ZnTe and b-(N 2 H 4 ) 2 ZnTe, have been isolated with slightly different conformation for the extended ZnTe chains.…”

“…[44,46] CuInTe 2 proved to be a particularly interesting example because the zinc-blende analog is not substantially soluble in hydrazine, thereby requiring the development of a modified approach for deposition, and it also represents a first example of deposition of a telluride-based system using the hydrazine-based approach (another example is ZnTe). [43] Crystals of CuInTe 2 also offer a band gap of %1 eV and relatively high Hall mobilities (p-type transport), ranging from 30 to 150 cm 2 V À1 s À1 , depending upon preparation conditions. [61][62][63] Since CuInTe 2 does not significantly dissolve in hydrazine, a new stepwise process was devised for dissolution, which involves separate indium-and copper-based precursor solutions.…”