Study of interfacial and microstructural state in 𝑮𝒂𝑵⁄𝑨𝒍𝟐𝑶𝟑 heterostructure

Abstract

Gallium nitride (GaN) films were grown in successive stages on c-plane sapphire substrates treated with silicon nitride (SiN) by metalorganic chemical vapour deposition. Growth started with nitridation of the substrate of the sapphire, followed by treatment with SiN. The film growth was interrupted at various stages to monitor film coalescence by in situ laser reflectometry. The only difference between the explored samples is the thickness, i.e., 0.12, 0.8, 2, and 4.5𝜇𝑚. In order to analyse stress, tilt and twist mosaicity, and electrical properties at all growth phases, Hall effect and High-resolution X-ray diffraction estimates were performed. In the 2θ = (20–80) degree range, the XRD spectra of the films were determined utilizing a high-resolution diffractometer fitted with a four-fold Ge (2 2 0) monochromator utilizing a Cu𝐾𝛼1 radiation source with a wavelength of 𝜆Cu𝐾𝛼1 = 0.154056 nm. The rocking curve full width at half maximum (FWHM) of four planes (00.2), (10.3), (10.2), and (10.1) were measured for each sample. As a function of the thickness, the evolution of the microstructure of GaN layers was monitored. A tilt and twisted mosaic drop with increasing thickness at different rates was seen in the results of this analysis. The interaction between the tilt and twist mosaic (m) increased during the coalescence process and remained practically consistent for completely coalesced layers. Measurements of the Hall effect showed that carrier concentration and mobility have the same twist and tilt mosaic sensitivity. Conversely, in symmetric and asymmetric (𝜔/2θ) scan mode, the a and c lattice parameters and the in-plane 𝜀𝑎 and out-of-plane 𝜀� strains were determined. Therefore, the different stress levels (thermal, intrinsic, and hydrostatic) should be calculated from these parameters. In addition, from the rocking curve scan mode, measurement of the FWHM of the (hk.l) reflections gives an idea of the defect density. At room temperature (300 k), the compressive stress (𝜎𝑎) increased with increasing layer thickness and reached a maximum level of − 0.45 GPa when the 2D growth mode was established. In addition, the concentration of native defects was determined. Compared with the properties of the untreated GaN grown layer, the effects of SiN treatment on mosaicity and stress evolution were discussed. The results are supported by images from an atomic force microscope (AFM), which showed a good surface morphology with a defect density of approximately 5× 108 cm−2 . At last, the determined stress level and defect density were used to explain some physical properties of the epitaxial GaN layers.