Correlation of crystalline defects with photoluminescence of InGaN layers

Abstract

We report structural studies of InGaN epilayers of various thicknesses by x-ray diffraction, showing a strong dependence of the type and spatial distribution of extended crystalline defects on layer thickness. The photoluminescence intensity for the samples was observed to increase with thickness up to 200 nm and decrease for higher thicknesses, a result attributed to creation of dislocation loops within the epilayer. Correlation of physical properties with crystalline perfection open the way for optimized designs of InGaN solar cells, with controlled types and dislocation densities in the InGaN epilayers, a key requirement for realizing high photocurrent generation in InGaN.

Microstructures produced during the epitaxial growth of InGaN alloys

“…For example, strained epitaxial layers in semiconductor systems are [39], and Potin et al [40]) for GaInN. Open data points= single phase; half-filled data points = metastable; filled data points= 2 phase mixtures.…”

“…In fact, the non-equilibrium growth of immiscible III/V alloys by OMVPE has been shown to be possible for many alloys [13]. For thick InGaN epilayers, the beginnings of PS by spinodal decomposition occur during OMVPE growth for alloys within the miscibility gap [34][35][36][37][38][39]. This gives rise to experimentally observed compositional fluctuations within the epitaxial layer.…”

“…2. The experimental data [34][35][36][37][38][39][40][41] will be discussed below. Later, more detailed VFF and first principles calculations [42] indicate that the equilibrium solubility may even be slightly smaller.…”

Phase separation in strained epitaxial InGaN islands

“…Since the early study of Ho and Stringfellow, 5 work has been done to study PS in epitaxial InGaN layers both theoretically and experimentally. [6][7][8][9] InGaN layers coherently grown on GaN are under compressive strain. This compressive strain tends to suppress PS of InGaN layers at typical growth temperatures.…”

Investigation of the main correlations between structural and physical propertiess of InAs quantum dots, embedded between strain-relief GaAsSb layers

“…For perfect epitaxial layer(s) interference fringes should be on and strong. Any diminutions of vertical coherence length in comparison with substrate extinction length or layer thickness and diffusion of interference patterns are usually related with structural deteriorations, caused by extended crystal defects, created in the volume of substrate and/or epitaxial layer(s) [12][13][14]. Density of threading segments of dislocation loops and lateral coherence length of substrate and GaAsSb epitaxial layers were determined from parameters of TC RCs, measured at the maximum of substrate or GaAsSb diffraction peaks of -2 RCs [15].…”