[Ge(TenBu)4] – a single source precursor for the chemical vapour deposition of germanium telluride thin films

Abstract

Reaction of activated germanium with ⁿBu₂Te₂ in THF solution was shown to be more effective for the preparation of the germanium(IV) tellurolate compound, [Ge(TeⁿBu)₄], than reaction of GeCl₄ with LiTeⁿBu in a 1 : 4 molar ratio in THF. The product was characterised by ¹H, ¹³C{¹H} NMR spectroscopy and microanalysis and evaluated as a single source precursor for the low pressure chemical vapour deposition of GeTe thin films. Depending upon deposition conditions, either dull grey films (predominantly elemental Te) or highly reflective (GeTe) films were obtained from the pure precursor. Grazing incidence X-ray diffraction shows that the highly reflective films are comprised of the rhombohedral α-GeTe phase, while scanning electron microscopy and energy dispersive X-ray analysis reveal rhomb-shaped crystallites with a 49(1) : 51(1)% Ge : Te ratio. This structure is also confirmed from Raman spectra. Van der Pauw measurements show ρ = 3.2(1) × 10⁻⁴ Ω cm and Hall electrical measurements indicate that the GeTe thin films are p-type, with a mobility of 8.4(7) cm² V⁻¹ s⁻¹ and carrier concentration of 2.5(2) × 10²¹ cm⁻³. The high p-type concentration is most likely a result of the substantial Ge vacancies in its sub-lattice, in line with the EDX elemental ratios.