Interfacial Chemistry Study of GaN by Trimethylaluminum-Only Cycles and X-ray Photoelectron Spectroscopy

The interfacial chemistry of n-type Ga-face GaN during atomic layer deposition of Al2O3 is studied by preceding the deposition process with several trimethylaluminum(TMA)-only cycles to clarify the impact of this precursor on the Al2O3/GaN interface. X-ray photoelectron spectroscopy analysis shows that the TMA precursor can react with the surface gallium oxide (GaOx) and convert the latter into aluminum oxide (AlOx), in accordance to past reports. However, the extent of conversion is limited as the reaction between TMA and GaOx is saturated after the first few TMA-only cycles. On the other hand, we found that the Ga/N ratio (GaN stoichiometry) is increased with the number of TMA-only cycles. At the same time, the Al-N bond peak appears in the Al 2p core-level spectrum, and its intensity also increases with the number of TMA-only cycles. The latter points to the formation of an Al-N layer, which may be attributed to Al ions from the TMA metal precursor penetrating the AlOx/GaOx layer and reacting with the underlying GaN. The reaction results in a loss of N from Ga bonding sites, and the increase of the Ga/N ratio. The resultant AlN layer protects the underlying GaN from oxidation and forms a high-quality interface with the Al2O3.