X-Ray Photoelectron Spectroscopy Characterization of Aluminum Nitride Surface Oxides: Thermal and Hydrothermal Evolution

Abstract

Oxidized surfaces of aluminum nitride (AlN) epilayers grown on sapphire substrates and of AlN bulk crystals grown by physical vapor transport were studied by x-ray photoelectron spectroscopy (XPS). Analysis of the oxygen core level spectra showed approximately equal contributions from oxygen in two bonding states, which were identified by the binding energies and relative separation of the fitted peaks as OH ) and O 2) . The oxide on air-exposed AlN surfaces was identified as aluminum oxide hydroxide. Systematic annealing experiments were conducted in vacuum to study the thermal evolution of hydroxide layers, and a dehydration mechanism resulting in the formation of Al 2 O 3 at high temperature was identified.

Native oxide and hydroxides and their implications for bulk AlN crystal growth

“…In this case, the reactions might involve (1) 2Al(OH) 3 25 supports the probability of reactions 1 and 2 occurring. Similar conclusions were drawn from XPS analysis by Dalmau et al; 19 an oxygen peak characteristic of a hydroxide was reduced by annealing for 6 h from 260 °C to 830 °C under ultrahigh vacuum. The intensity of XPS oxygen peaks changed in a manner indicating a shift in the surface composition from AlOOH toward Al 2 O 3 with increasing temperature.…”

“…18,19 Its formation occurs rapidly, within a few minutes. Panchula and Ying 18 followed the formation of native hydroxides on freshly prepared nanocrystalline AlN upon exposure to oxygen and water vapor in ambient air by photo-acoustic Fourier transform infrared spectroscopy.…”

“…From x-ray excited Auger electron spectrum (XANES) measurements, Kameshima et al 21 concluded that the oxide thickness of AlN powders produced by carbothermal means was twice as thick (1.1 nm) as those found on AlN powders produced by direct nitridation (0.5-0.6 nm). Also using XPS, Dalmau et al 19 concluded that the limiting thickness of AlOOH on AlN (0001) exposed to air was 1.2 nm.…”

“…The intensity of XPS oxygen peaks changed in a manner indicating a shift in the surface composition from AlOOH toward Al 2 O 3 with increasing temperature. 19 At sufficiently high temperatures (more than 1500 °C), in the presence of Al vapor (which is produced by the sublimation of AlN), the oxide can be removed by forming volatile oxygen species. 26 The most probable reaction is (3) Al 2 O 3 + 4 Al(g) = 3Al 2 O.…”

Structural and chemical analysis of annealed plasma-enhanced atomic layer deposition aluminum nitride films

“…Similar results have been reported by Ansart et al 26 who concluded that no chemical alterations of AlN deposited with plasma-enhanced CVD took place below 850 C in air and that transformation to a-Al 2 O 3 took place rapidly above 1100 C in air. Dalmau et al 27 reported AlN to form a thin layer ($1 nm) of AlOOH at room temperature under ambient-air exposure. This layer then approached the stoichiometry of Al 2 O 3 when annealed under vacuum in higher temperatures.…”