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

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

Samples	Al₂O₃ thickness (nm)	Ratio	Detection angles θ
Samples	Al₂O₃ thickness (nm)	Ratio	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