Indium nitride (InN) is an interesting material for future electronic and photonic-related applications, as it combines high electron mobility and low-energy band gap for photoabsorption or emission-driven processes. In this context, atomic layer deposition (ALD) techniques have been previously employed for InN growth at low temperatures (typically < 350 C), reportedly yielding crystals with high quality and purity. In general, this technique is assumed to not involve any gas phase reactions as a result from the time-resolved insertion of volatile molecular sources into the gas chamber. Nonetheless, such temperatures could still favour the precursor decomposition in gas phase during the In half-cycle, therefore altering the molecular species that undergoes physisorption and, ultimately, driving the reaction mechanism to pursue other pathways. Thence, we herein evaluate the thermal decomposition of relevant In precursors in gas phase, namely trimethylindium (TMI) and tris(N,N-diisopropyl-2-dimethylamido-guanidinato) (III) (ITG), by means of thermodynamic and kinetic modelling. According to the results, at T= 593 K, TMI should exhibit partial decomposition of ~8% after 400 s to first generate methylindium (MI) and ethane (C2H6), a percentage that increases to ~34% after 1 hour of exposure inside the gas chamber. Therefore, this precursor should be present in an intact form to undergo physisorption during the In half-cycle of the deposition experiment (< 10 s). On the other hand, the ITG decomposition starts already at the temperatures used in the bubbler and it will slowly decompose as it is evaporated during the deposition process. At T= 300 C, the decomposition is a fast process that reaches 90% completeness after 1 s, and where equilibrium, at which almost no ITG remains, is achieved before 10 s. In this case, the decomposition pathway is likely to occur via elimination of carbodiimide ligand. Ultimately, these results should contribute for a better understanding of the reaction mechanism involved in the InN growth from these precursors.
Thermal Decomposition of Trimethylindium and Indium Trisguanidinate Precursors for InN Growth: An Ab-Initio and Kinetic Modelling Study
Thermodynamic Data for the first decomposition of TMI in different levels of theory; Time-dependent evolution of trimethylindium (TMI) and ITG decomposition in other temperature conditions; Transition state structures that are relevant for TMI decomposition