Structure Analysis of GaN Thin Film with Inversion Domains by High Voltage Atomic Resolution Microscopy

Abstract

The atomic structures and surface morphologies of three types of GaN films were investigated by high voltage atomic resolution microscopy (HVARM). By HVARM, each atomic column of Ga and N could clearly be resolved and the polarity of the film and inversion domains could be directly determined. The GaN film was grown on a sapphire substrate by molecular beam epitaxy (MBE) after nitridation of the sapphire surface. Inversion domains (IDs) crossed the whole film to the surface and made small pyramids on the surface. The small pyramids had Ga-polarity and the rest had N-polarity. A GaN film with In exposure during film growth had an almost Ga-polarity flat surface. In exposure process reduced the density of inversion domains that have a N-polarity. While a GaN film grown on an AlN buffer layer was unipolar, with a Ga-polarity. HVARM observation revealed that the density of the IDs determine the qualities and the polarity of the film.

Low Voltage Transmission Electron Microscopy of Graphene

“…Pushing this relationship to extremes to improve resolution has been done. An example is the JEOL ARM1250 TEM, which is capable of operating with electron acceleration voltages of up to 1 MeV, and has a resolution of ∼1 Å for light atoms such as carbon and nitrogen in SiC and GaN …”

Advanced semiconductor characterization with aberration corrected electron microscopes

“…The difficulty was first to calibrate the microscope as the lenses can introduce a 180° rotation between the image and the diffraction pattern, and to obtain local diffraction maps. Alternative solutions have been proposed: HRTEM image analysis [18,19,20], HAADF-STEM image [21,22], or more recently Annular Bright Field (ABF) STEM images [23,24,25,26]. Before the introduction of Cs-correctors, the analysis of HRTEM was not very robust unless a high voltage microscope was used [18].…”

“…Alternative solutions have been proposed: HRTEM image analysis [18,19,20], HAADF-STEM image [21,22], or more recently Annular Bright Field (ABF) STEM images [23,24,25,26]. Before the introduction of Cs-correctors, the analysis of HRTEM was not very robust unless a high voltage microscope was used [18]. Indeed, the determining of polarity relied on the shape of a profile made along a narrow inclined line [19], but the difference between the two polarities was faint and the HRTEM contrast is very sensitive to tilt, thickness and defocus.…”