Abstract
Interfaces in Al2O3/n-GaN capacitors fabricated on free-standing GaN substrates were investigated using sub-bandgap photo-assisted capacitance-voltage measurements. After post-metallization annealing (PMA) at 300 °C, the metal-oxide-semiconductor (MOS) devices exhibited excellent capacitance-voltage (C-V) characteristics without frequency dispersion under dark conditions and a quite low interface state density (Dit) of ∼7×1010 cm-2 eV-1 for energies less than ∼1.2 eV from the conduction band edge. Despite the outstanding characteristics under dark conditions, it was found that sub-bandgap irradiation also resulted in shifts of the C-V curves toward the negative bias direction, which indicates the existence of donor-type interface traps. As a result, the Al2O3/n-GaN Dit distribution does not show the generally reported U-shape: for energies less than ∼1.2 eV from the conduction band edge, a Dit of ∼7×1010 cm-2 eV-1 was observed, although Dit rapidly increased to ∼2-4×1012 cm-2 eV-1 near the valence band edge. These interface states near the valence band edge are positively charged due to trapped holes when the states are located above the Fermi level.
Highlights
Al2O3/GaN interface properties have been investigated using electrical, optical and structural characterization methods, and with first-principles calculations.[12–34] Among the reported results, the importance of the post-deposition annealing (PDA) process after atomic layer deposition (ALD) of Al2O3 was suggested to reduce the interface state density (Dit).[12–15,28] the process is not yet fully established
The Al2O3/n-GaN Dit distribution does not show the generally reported U-shape: for energies less than ∼1.2 eV from the conduction band edge, a Dit of ∼7×1010 cm-2 eV-1 was observed, Dit rapidly increased to ∼2-4×1012 cm-2 eV-1 near the valence band edge
post-metallization annealing (PMA) at even lower temperatures such as 300-600 ○C was reported to be effective for the reduction of Dit, probably due to the considerable progress that has been made in ALD techniques and the improved scitation.org/journal/adv crystal quality of GaN epitaxial layers grown on GaN bulk substrates with low dislocation densities.[13–15]
Summary
Al2O3/GaN interface properties have been investigated using electrical, optical and structural characterization methods, and with first-principles calculations.[12–34] Among the reported results, the importance of the post-deposition annealing (PDA) process after atomic layer deposition (ALD) of Al2O3 was suggested to reduce the interface state density (Dit).[12–15,28] the process is not yet fully established.
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