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Table 2 Summary of the peak intensity ratio of Ga–O to Ga–N, Ga to N, and the corresponding XPS sampling depth at different detection angles θ

From: Investigation on Surface Polarization of Al2O3-capped GaN/AlGaN/GaN Heterostructure by Angle-Resolved X-ray Photoelectron Spectroscopy

Samples Al2O3 thickness (nm) Ratio Detection angles θ
27.5° 42.5° 57.5° 72.5°
S1 1 Ga–O/Ga–N 0.19 0.19 0.23 0.25
Ga/N 2.03 1.69 1.60 1.59
Ga–N BE sampling depth (nm) 8.0 6.5 4.5 2.1
S2 3 Ga–O/Ga–N 0.19 0.17 0.2 0.16
Ga/N 1.92 1.72 1.85 1.69
Ga–N BE sampling depth (nm) 6.0 4.5 2.5 0.1
S3 3 Ga–O/Ga–N 0.23 0.33 0.27 0.28
Ga/N 0.94 1.15 1.39 1.09
Ga–N BE sampling depth (nm) 6.0 4.5 2.5 0.1
  1. Sampling depth = 3λcosθ—the capping Al2O3 thickness