A Comparative Study of Low-Temperature III-V Nitrides ALD in Thermal and Radical-Enhanced Modes

This paper explores the possibility of Atomic Layer Deposition (ALD) of polycrystalline GaN thin films in a purely thermal mode from trimethylgallium (TMG) and ammonia (NH3) precursors, at a temperature as low as 400 oC, without any additional activation, e.g., by a plasma. In order to achieve this, the so-called adduct chemical pathway, prevalent in GaN Metal Organic Chemical Vapor Deposition (MOCVD), was realized within an ALD scheme. Based on the known existence of the TMG:NH3 adduct in gasphase, here we hypothesize the occurrence of an analogous TMG:NH3 surface adduct, and thereby propose a model for the growth of GaN via surface reactions occurring in a self-limiting
manner. We show that such surface reactions are possible even at 400 oC, and result in polycrystalline GaN films with a reasonable growth rate of 0.045 nm/cycle. The proposed purely thermal low temperature deposition approach may increase the versatility of poly-GaN films in several new applications.