Chalcogenoether complexes with Group 13 halides and development of single source precursors for chemical vapour deposition of III-V and III-VI thin films

Abstract

GaCl3 can react with macrocyclic thio- and seleno-ethers to give complexes with coordination numbers and geometries that were previously not accessible by using acyclic chalcogenoether ligands. [MCl2([16]aneE4)][MCl4] (M = Ga, In; E = S, Se) exhibit distorted octahedral geometry at M, whereas [GaCl3([14]aneS4)] is the first example of trigonal bipyramidal coordination at Ga with three planar chlorides. GaCl3 was also found to promote the one and two electron oxidation of [8]aneSe2 to [{[8]aneSe2}2][GaCl4]2 and [{[8]aneSe2Cl}][GaCl4].

The coordination complexes [GaCl3(nBu2E)] and (GaCl3)2{nBuE(CH2)nEnBu}] (E = Se, n = 2; E = Te, n = 3) have been found to be effective single source precursors for the LPCVD of Ga2E3 at 773 K. The films were shown to be stoichiometric and have low levels of impurities by EDX. It is possible to preferentially deposit Ga2Te3 onto TiN rather than SiO2. This is the first reported example of a precursor based on a telluroether and the first single source precursor to deposit single phase Ga2Te3.

[Ga(SiPr)2(?-SiPr)]2 can be used to deposit cubic Ga2S3 at 723 K, which can be annealed to give monoclinic Ga2S3. In situ XRD shows that the phase transition occurs between 773 and 873 K. The phase change also causes a change in the resistivity of the thin film. It is also possible to induce a phase change by laser annealing. Microfocus XRD and subsequent phase refinement was used to quantify the percentage conversion to the monoclinic phase, with higher laser powers giving a higher fraction of the monoclinic phase.

The reaction of AlX3 (X = Cl, Br, I) with acyclic chalcogenoethers yielded a range of coordination numbers and geometries. [AlX3(Me2E)] (E = S, Se, Te) had distorted tetrahedral coordination at Al; [AlCl3(MeC(CH2SMe)3)] formed a 1D chain polymer with trigonal bipyramidal coordination; [AlX2(MeECH2CH2EMe)2][AlX4] exhibited 6-coordinate Al. The reaction of AlCl3 with macrocyclic ligands formed [AlCl3([9]aneS3)], [AlCl2([14]aneS4)][AlCl4] and [AlCl2([16]aneSe4)][AlCl4]. All complexes were very air and moisture sensitive and AlCl3 was found to promote the formation of selenonium and telluronium species. [AlCl3(nBu2E)] (E = Se, Te) were found to be unsuitable precursors for LPCVD of aluminium chalcogenide thin
films.

[nBu2Ga(?-EtBu2)2GanBu2] (E = P, As) were used to deposit thin films of GaP and GaAs via LPCVD. The films were crystalline and had low levels of C and O contamination. The thin films of GaP were found to exhibit photoluminescence comparable to that of a single crystal reference, whereas GaAs exhibited some sub-band gap luminescence. [Ga(PtBu)3] was investigated as a single source precursor but was found to be unsuitable due to poor volatility.

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ORCID for Gillian Reid: orcid.org/0000-0001-5349-3468

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