Chemistry and electrical properties of surfaces of GaN and GaN/AlGaN heterostructures

TLDR: In this article, the surface passivation process of GaN utilizing SiNx film by electron-cyclotron-resonance assisted plasma chemical vapor deposition (ECR-CVD) achieved low interface state density, 2×1011cm−2'eV−1.

Abstract: Chemical and electrical properties of the surfaces of GaN and GaN/AlGaN heterostructures were systematically investigated by x-ray photoelectron spectroscopy (XPS), capacitance–voltage, and current–voltage measurements. From in situ XPS study, relatively smaller band bending of 0.6 eV was seen at the GaN (2×2) surface grown by radio frequency-assisted molecular beam epitaxy on the metalorganic vapor phase epitaxy GaN template. After exposing the sample surface to air, strong band bending took place at the surface. The surface treatment in NH4OH solution and N2 plasma was found to reduce the surface Fermi level pinning. Surface passivation process of GaN utilizing SiNx film by electron-cyclotron-resonance assisted plasma chemical vapor deposition (ECR–CVD) achieved low interface state density, 2×1011cm−2 eV−1. No pronounced stress remained at the SiNx/GaN interface, which was confirmed by Raman spectroscopy. The present NH4OH/ECR–N2 plasma treatment was also found to be effective in realizing well-ordered ...

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FIG. 7. In situ XPS Al 2p spectra of the NH4OH-treated GaN/AlGaN/Al sample prepared in the MBE chamber~a! before and~b! after the UHV anneal at 700 °C for 10 min.

FIG. 11. Profiles of electron concentration near the GaN/AlGaN interface as a function of distance from the top AlGaN surface. The measuredC–V curves on the Pt/Au Schottky gates are shown in the inset.

FIG. 8. Distributions of interface state density (D it) of the fabricatedn-GaN MIS structures. TypicalC–V data obtained from the NH4OH/ECR–N2 plasma passivated sample were plotted in the inset.

FIG. 10. I –V characteristics of the Pt/Au Schottky contacts with and without an Al-oxide interface layer fabricated on the NH4OH-treated surface of GaN/AlGaN heterostructures.

FIG. 9. I –V characteristics of the gateless GaN/AlGaN HEMT structure with and without SiNx surface passivation.

FIG. 3. ~a! O 1s spectra of the MOVPE sample after the air exposure and the NH4OH/N2 plasma treatments, and~b! change in the XPS integrated intensity of the O 1s level normalized by the N 1s level.