Structural and optical properties of InGaN/GaN layers close to the critical layer thickness

Abstract

In this work, we investigate structural and optical properties of metalorganic chemical vapor deposition grown wurtzite InxGa1−xN/GaN epitaxial layers with thicknesses that are close to the critical layer thickness (CLT) for strain relaxation. CLT for InxGa1−xN/GaN structures was calculated as a function of the InN content, x, using the energy balance model proposed by People and Bean [Appl. Phys. Lett. 47, 322 (1985)]. Experimentally determined CLT are in good agreement with these calculations. The occurrence of discontinuous strain relaxation (DSR), when the CLT is exceeded, is revealed in the case of a 120 nm thick In0.19Ga0.89N layer by x-ray reciprocal space mapping of an asymmetrical reflection. The effect of DSR on the luminescence of this layer is clear: The luminescence spectrum shows two peaks centered at ∼2.50 and ∼2.67 eV, respectively. These two components of the luminescence of the sample originate in regions of different strain, as discriminated by depth-resolving cathodoluminescence spectroscopy. DSR leads directly to the emergence of the second, lower-energy, peak. Based on this experimental evidence, it is argued that the appearance of luminescence doublets in InGaN is not evidence of “quantum dotlike In-rich” or “phase separated” regions, as commonly proposed

Investigation of indium gallium nitride facet-dependent nonpolar growth rates and composition for core–shell light-emitting diodes

“…On the NRs, increased surface roughness of the c-plane is observed, indicating a layer of unstrained indium rich growth. 31,32 On the macroscale, the different crystal planes are known to have different relative growth rates 30 determined by growth parameters 33,34 and potentially result in different InN mole fractions on the crystal planes, as shown by previous work. 4,17,29 However, it is unclear if the growth dynamics on rod-shaped nanostructures will be the same.…”

Comparison of the Luminous Efficiencies of Ga- and N-PolarInxGa1−xN/InFernández-Garrido1, Lähnemann2, Hauswald3 et al. 2016Phys. Rev. Applied171140View full textAdd to dashboardCite

“…6(c) also reveals the presence of a-type misfit dislocations (MDs) in sample I, well below the onset of significant plastic relaxation of the entire film in In x Ga 1−x N layers on GaN. [38][39][40][41] Note, however, that plastic relaxation is only observed locally. Local plastic relaxation can be induced by spatial variations in the growth mode caused by fluctuations in the growth conditions or by the presence of structural and/or morphological defects.…”

Defects, strain relaxation, and compositional grading in high indium content InGaN epilayers grown by molecular beam epitaxy

“…27,28 Above h cr , reciprocal space x-ray diffraction (XRD) maps of asymmetrical reflections often exhibit double points associated with discontinuous strain relaxation along the growth direction, and what may also be a chemical discontinuity. Strain discontinuity but no compositional gradient was reported in 120 nm thick In 0.19 Ga 0.81 N. 29 Liliental-Weber et al 30 studied In 0.28 Ga 0.72 N and In 0.40 Ga 0.60 N epilayers using transmission electron microscopy (TEM) and correlated the double points to a selfformed pseudomorphic InGaN interlayer between the main film and the substrate, which was termed a "sequestration layer" (SQL) and had lower indium concentration (0.17 in the first case and 0.23 in the second). Contrary to the SQL, the main epilayer was very rich in basal stacking faults (BSFs).…”