Abstract
This study assesses the characteristics (edge and screw dislocation density) of a commercially available GaN/AlN/Al2O3 wafer. The heterostructure was evaluated by means of high-resolution X-ray diffraction (HR-XRD), high-resolution transmission electron microscopy (HR-TEM), and Doppler-Broadening Spectroscopy (DBS). The results were mathematically modeled to extract defect densities and defect correlation lengths in the GaN film. The structure of the GaN film, AlN buffer, Al2O3 substrate and their growth relationships were determined through HR-TEM. DBS studies were used to determine the effective positron diffusion length of the GaN film. Within the epitaxial layers, defined by a [GaN (0 0 0 2) || AlN (0 0 0 2) || (0 0 0 2) Al2O3] relationship, regarding the GaN film, a strong correlation between defect densities, defect correlation lengths, and positron diffusion length was assessed. The defect densities 6.13 × 1010 cm−2, 1.36 × 1010 cm−2, along with the defect correlation lengths Le = 155 nm and Ls = 229 nm found in the 289 nm layer of GaN, account for the effective positron diffusion length Leff~60 nm.
Highlights
Gallium nitride, GaN, and its alloys are mostly studied because of their usage in optoelectronic and high-temperature electronic device applications [1,2]
This study relies on a gallium nitride thin film grown on sapphire and purchased from NTT
Advanced sample preparation has a crucial role in a successful Transmission Electron Microscopy (TEM) characterization process; the sample was first mechanically polished, etched with an ion beam until perforation
Summary
GaN, and its alloys are mostly studied because of their usage in optoelectronic and high-temperature electronic device applications [1,2]. Different applications that require either electron [3] or hole injection [4] for different devices imply the use of either n-type or p-type semiconductors. Besides injection layers in heterostructures, GaN layers can be used as free-standing films is applications that require “defect free” semiconductors with wide band gaps. The antiparticles of electrons, can be obtained from radioactive nuclides and normally possess high energy values. They can be used to study thin films or the areas near the surface, with one condition—they need to be slowed down, in order to obtain low-energy positrons. One of the potential uses for defect free GaN films is in the field of positron moderation and field-assisted moderation
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