Chemical Vapor Deposition of Hexagonal Gallium Selenide and Telluride Films from Cubane Precursors: Understanding the Envelope of Molecular Control

Gallium selenide (GaSe) thin films have been grown at 325−370 °C by atmospheric pressure metal−organic chemical vapor deposition (AP-MOCVD) using the single-source precursors [(R)Ga(μ 3 -Se)] 4 (R = CMe 3, CEtMe 2, and CEt 2 Me). In contrast, the growth of gallium telluride from [(R)Ga(μ 3 -Te)] 4 is accomplished at 285−310 °C by low-pressure metal−organic chemical vapor deposition (LP-MOCVD). Characterization of the films by Auger electron spectroscopy (AES), Rutherford backscattering (RBS), and wavelength-dispersive spectroscopy (WDS) microprobe analysis shows all the films to have Ga:E (E = Se, Te) compositions of 1:1 with a low degree of impurities (C < 2%; O < 0.1%). From X-ray diffraction (XRD) and transmission electron microscopy (TEM) the GaSe and GaTe films were found to be polycrystalline hexagonal layered GaE structures, with a preferred c -axis orientation independent of substrate. For GaSe this represents the thermodynamically stable phase, while hexagonal GaTe is a metastable phase that converts to the thermodynamic monoclinic form on annealing at 500 °C. Diffraction results yield appropriate lattice parameters of a = 4.1 Å (TEM) and c = 16.38 Å (XRD) for hexagonal GaTe. Crystallite and particle size measurements reveal that the as-deposited films consist of oriented ca. 10 nm crystalline particles. The formation of these hexagonal layered structures is proposed to occur as a consequence of the fragmentation of the cubane's Ga 4 E 4 core during deposition, and the formation of trimeric “Ga 3 E 3 ” building blocks.