Spatially modified layer properties related to the formation of gallium droplets on GaN(0001) surfaces during plasma-assisted molecular-beam epitaxy

Abstract

The surface morphology and the spatial distribution of defect-related luminescence of GaN(0001) layers grown by plasma-assisted molecular-beam epitaxy under gallium-rich conditions has been investigated. Droplets of liquid gallium form on the surface during growth and lead to distinct spiral hillocks under the droplet. The droplets are surrounded by extended voids which point to an incomplete gallium adlayer on the GaN surface during growth at the droplet boundary. Cathodoluminescence spectra indicate an enhanced intensity in the yellow spectral range for the GaN under the droplets which is attributed to a change in the local density of point defects in the layer.

AlGaN/GaN HEMTs on free-standing GaN substrates: MBE growth and microwave characterization

“…The etched surfaces exhibited root-mean-square roughnesses as low as Table 1 Sample ID, substrate growth temperature, Ga BEP, Hall mobility, electron sheet density, sheet resistance (by CTLM), saturated drain current density (at source-drain voltage V DS ¼ 10 V and gate-source voltage V GS ¼ 0), and gate leakage current 2.8 Å , and the surface morphologies between droplets were similar to those previously reported elsewhere [14,18]. The morphology of regions under Ga droplets in similarly grown samples is consistent with those reported by Kruse et al [19]. However, as yet we have not identified any correlation between AlGaN surface morphology and electronic properties of AlGaN/GaN HEMTs.…”

In as a surfactant for the growth of GaN (0001) by plasma-assisted molecular-beam epitaxy

“…As we showed in a previous publication, these droplets change locally the surface morphology and the bulk properties of GaN. 3 The use of a surfactant is an approach to influence the surface morphology of GaN without the drawbacks associated with a gallium-rich growth described above. The used atomic species is supposed to enhance the surface migration of gallium and/or nitrogen without being incorporated into the crystal by itself.…”

Stress evolution of GaN/AlN heterostructure grown on 6H-SiC substrate by plasma assisted molecular beam epitaxy

“…The poor surface below the droplets has been found to degrade the bulk properties of GaN. 22 Thus, "modulated growth" was performed in order to obtain atomically smooth surfaces without droplet formation. The barrier and cap layers were grown with no growth interruption at a constant Ga flux.…”