Correlation on GaN epilayer quality and strain in GaN-based LEDs grown on 4-in. Si(1 1 1) substrate

Morphology Evolution of Gradient-Alloyed CdxZn1–xSeyS1–y@ZnS Core–Shell Quantum Dots during Transmission Electron Microscopy Determination: A Route to Illustrate Strain Effects

“…Although many materials have been explored, most of the efficient EL and PL devices still rely on the well-developed CdSe QDs. − Especially, Cd x Zn 1– x Se y S 1– y @ZnS core–shell QDs are prime candidates in current light-emitting applications . In conventional semiconductor devices, the strain induced by lattice mismatch has been well known to affect the device performance. , Accordingly, strain effects are more pronounced for core–shell QDs than their bulk counterparts, which significantly influences their PL properties and stability. − Alloyed Cd x Zn 1– x Se y S 1– y @ZnS core–shell QDs, with a chemical composition gradient, reduce the lattice mismatch as well as interfacial strain effects, providing alternative materials for light-emitting applications . For example, Yang et al achieved optimized performance and stability of QD LEDs by controlling the shell gradients .…”

“…In bulk materials, the interfacial strain in heterostructures has been investigated by applying PL and Raman measurements. , Although the spectroscopic measurements are convenient and accurate on the micrometer scale, it is a great challenge to achieve spatial resolution on the nanometer scale because of the limitation of light wavelength and focusing property. X-ray diffraction (XRD) could be effective to determine the strain effects in nanoscale materials; however, the analysis was usually limited by the intrinsic broadened peaks due to the small size and gradient compositions. , This hindered the strain study in core–shell QDs.…”

“…6 In conventional semiconductor devices, the strain induced by lattice mismatch has been well known to affect the device performance. 7,8 Accordingly, strain effects are more pronounced for core−shell QDs than their bulk counterparts, which significantly influences their PL properties and stability. 9−12 Alloyed Cd x Zn 1−x Se y S 1−y @ZnS core−shell QDs, with a chemical composition gradient, reduce the lattice mismatch as well as interfacial strain effects, providing alternative materials for light-emitting applications.…”

Growth of Single-Crystalline GaN Films on Ga-Free Langasite-Type Crystals by Metal–Organic Chemical Vapor Deposition

“…The three peaks observed are attributed to the A 1 (TO), E 2 (high), and A 1 (LO) of GaN epitaxial films. The E 2 (high) is commonly used to characterize the residual stress of GaN films, and the wavenumber of 568 cm –1 is reported to be the stress-free bulk GaN layer . The stress of GaN films could be calculated by the following equation: σ = normalΔ ω / k where “σ” is the stress, “Δω” is the shift of E 2 (high) peak, and “ k ” is the Raman stress coefficient (4.3 cm –1 GPa –1 ).…”

Transferable GaN Films on Graphene/SiC by van der Waals Epitaxy for Flexible Devices

“…The strain was calculated by Equation as follows: where Δω is the E 2 ‐high peak shift and σ is the stress value. There is no obvious change in the E 2 ‐high peak position of the GaN films before and after release (567.8 cm −1 ), which is close to the reported stress‐free GaN (568 cm −1 ) . The cumulative strain of the GaN films is very small (−0.04 GPa), which confirms the release effect of graphene from the internal stress of the GaN films.…”