Correlation of Optical, Structural, and Compositional Properties with V-Pit Distribution in InGaN/GaN Multiquantum Wells

Abstract

InGaN/GaN double heterostructures and multiquantum wells (MQWs) have been successfully developed since more than 20 years for LED lightning applications. Recent developments show that state-of-the-art LEDs benefit from artificially generated V-pit defects. However, the control of structural and chemical properties plays a tremendous role. In this paper, we report on the lateral distribution of V-pit defects and photoluminescence of InGaN/GaN MQWs grown on thick GaN on patterned sapphire substrates. The synchrotron-based scanning X-ray diffraction microscopy technique K-map was employed to locally correlate these properties with the local tilt, strain, and composition of the InGaN/GaN MQW. Compositional fluctuation is the main factor for the variation of photoluminescence intensity and broadening. In turn, V-pit defects align along small-angle grain boundaries and their strain fields are identified as a reason for promoting the InGaN segregation process on a microscale.

Nanoscale mapping of the full strain tensor, rotation and composition in partially relaxed In$_x$Ga$_{1-x}$N layers by scanning X-ray diffraction microscopy

“…3(a) shows that this loss of In is connected to an increased V-pit density. Such a reduced In concentration near V-pits has already been observed before [21]. It may be the result of a disturbed growth such as changes in the relative diffusion of In and Ga due to the high defect density.…”

“…In general, we can see variations on the micrometer scale in all of the experimental maps which has been observed in In x Ga 1 -x N films before [21,40]. It also appears that the lattice parameters, strains and rotations of the top InGaN layer vary on longer length scales compared to the seed layer.…”

“…Today, the spatial resolution at state-of-the-art beamlines is in the several 10 nm range and SXDM gives direct, model-free information about the lattice parameters. Although the technique has already been applied to several material systems and devices to study strain and composition [20,21], former results were based on limited data and relied on the average crystallographic symmetry. However, on the microscopic scale, no symmetry of the unit cell can be presumed because of an anisotropic local stress.…”

Analysis of stress-induced inhomogeneous electroluminescence in GaN-based green LEDs grown on mesh-patterned Si (111) substrates with n-type AlGaN layer*

“…[23] Besides, the enlarged FLM near the edge of the pattern unit in the inset shows that the InGaN QWs emit a longer wavelength near the trench. The higher indium content in the QWs may relate to the total amount of freestanding surfaces nearby, as suggested by Zoellner et al [24] Based on this stress-induced difference in indium composition, we divide the chip into two parallel diodes.…”

Thermal effect induced dynamically lasing mode tuning in GaN whispering gallery microcavities

“…Strategies to realize tunable luminescence of semiconductors can be divided into three groups: the first is based on energy-band engineering through changing the composition [12,13]. The design of a quantum well structure is the most desirable success for this method [14,15]. The second is based on the tuning of the cavities, including individual cavity size and coupled structures [16][17][18].…”