Two to three dimensional transitions of InGaN and the impact of GaN overgrowth

Abstract

The heteroepitaxial growth of InGaN on GaN was studied by in-situ reflection high-energy electron diffraction, atomic force microscopy, scanning tunneling microscopy and transmission electron microscopy. The misfit strain between InGaN and GaN was relaxed by the deposition of a few-nm-thick wetting layer and the subsequent formation of nano-islands without misfit dislocations, which is the so-called StranskiKrastanov growth mode. Thus, InGaN nano-islands with a very high density of around 10 12 cm -2 and a very small aspect ratio of ~2.1 (diameter/height) were achieved. In this paper, we also discuss the problems regarding GaN overgrowth of an InGaN nano-island layer.

Microstructures produced during the epitaxial growth of InGaN alloys

“…Of course, other growth conditions, particularly the growth rate, will also have major effects on the island size and density. For MBE growth, island densities of 10 11 cm À 2 have been reported, similar to those observed for OMVPE growth [81,83].…”

“…Either of these analyses, for equilibrium within the island or for a frozen-in In distribution, gives a process for the selfassembly of a series of In-rich clusters with a density equal to the density of islands, which has been reported to be as high as 10 12 cm À 2 in InGaN grown on GaN by OMVPE [81]. Importantly, when the island density is greater than the dislocation density, typically of the order of 10 8 cm À 2 in high quality epitaxial layers [7], the In-rich regions will capture the injected minority carriers in an LED where they will recombine radiatively before they can reach dislocations, where they would recombine non-radiatively.…”

“…After 12 ML coverage, the average diameter and height of the InGaN islands, with x =0.43, were 30 and 3 nm, respectively. Yamaguchi et al [58] reported the S-K growth of InGaN islands on GaN by both MBE and OMVPE. RHEED studies during MBE clearly showed a 2D to 3D transition as the InGaN layer thickness increased.…”

Microstructural and compositional analyses of GaN‐based nanostructures

“…In the present case, an InGaN island sample was grown at 510 8C and capped with an $2 nm thick GaN layer. To obtain a smooth film, the cap layer was deposited under gallium rich conditions [26]. The growth temperature of the cap layer was kept constant at 510 8C to minimise redistribution of indium during overgrowth with GaN.…”

Two‐step growth of InGaN quantum dots and application to light emitters

“…A typical method of growing QDs is the self-assembled formation of nano-islands and the subsequent growth of a capping layer [2][3][4][5]. However, the strain-driven selfassembled nano-islands have indium compositions largely varying between the bottom and the top of the islands [6]. The capping process causes significant changes in the size and shape of the QDs and sometimes results in the complete dissolution of the QDs [7] because of intermixing and strain relaxation during capping.…”