Compositions and properties of high-conductivity nitrogen-doped p-type β-Ga2O3 films prepared by the thermal oxidation of GaN in N2O ambient

Abstract

A remarkable improvement in the conductivity of grown nitrogen-doped p-type β-Ga2O3 films was successfully achieved via the thermal oxidation of GaN in N2O ambient at 1100 °C. In the vacuum test environment, its room temperature Hall hole concentration is 1.64 × 1017 cm−3, the Hall resistivity is 7.66 Ω cm, the Hall hole mobility is 4.98 cm2 V−1 s−1, and the acceptor ionization energy is 0.087 eV. In addition, the compositions and properties were also extensively investigated. When the oxidation temperature was raised from 900 to 1100 °C, the FWHM of the {2¯ 01}-oriented β-Ga2O3 diffraction peak from the X-ray diffraction (XRD) pattern decreased to 0.237°, confirming an improvement in the crystalline quality of the β-Ga2O3 nanocrystal structure. From both the cross-sectional view of the field emission scanning electron microscopy (FESEM) image and the cross-sectional lamellae prepared by focused ion beam (FIB) milling, it was observed that the generated β-Ga2O3 film transformed into a two-layer morphology when oxidized at 1100 °C. The top layer is a rather loose film composed of nanorods, and the selected area electron diffraction (SAED) pattern of a nanorod confirmed it as high-quality (6¯03)-dominated monocrystal β-Ga2O3. The second layer is a comparatively compact β-Ga2O3 film. This approach to the efficient growth of p-type β-Ga2O3 can broaden the applicability of these two-layered structures. The randomly distributed monocrystal nanorods on the top layer are an appropriate candidate for the photocatalyst, while the relatively more compact second layer with high p-type conductivity can be employed in high-performance solar-blind UV photodetectors or high-power electronic devices.