Completely merged multi-color asymmetric pyramid with suppressed stress and defect density

• Published in: Journal of crystal growth 2021-09, Vol.570, p.126215, Article 126215
• Main Authors: Tian, Zhenhuan, Zhang, Weihan, Wang, Xuzheng, Li, Qiang, Su, Xilin, Li, Yufeng, Yun, Feng
• Format: Article
• Language: English
• Subjects: Asymmetry; Color; Deep-hole pattern; Dislocation density; Display devices; Lateral overgrowth; Mass transfer; Microstructures; Piezoelectricity; Pyramids; Quantum wells; Residual stress; Sapphire; Spontaneous emission; Stress and defect; Substrates
• ISSN: 0022-0248; 1873-5002
• DOI: 10.1016/j.jcrysgro.2021.126215

•Obtain completely merged asymmetric pyramids by carefully designing substrate pattern.•Enlarge the emission range by mixture facets and lateral overgrowth.•Suppress the stress by deep-hole pattern and lateral overgrowth.•Annihilate the dislocation by dislocation bending and crystal nucleus coalescence.•These asymmetric pyramids can be used for display, flexible devices and VLC. The selective area growth (SAG) technique enables the creation of multi-color micro-structures. However, the substrate pattern to obtain multi-color and mass transfer of these micro-structures are complicated to achieve. Moreover, high dislocation density as well as large residual stress in c-plane quantum wells still remain challenges. Here, an improved SAG strategy was proposed to achieve completely merged asymmetric pyramids on closely connected deep-concave holes via the lateral overgrowth of adjacent pyramids. These asymmetric pyramids were directly grown on the sapphire substrate, making mass transfer be possible. Growth rate distinction appears at the different positions of the overgrowth region, resulting in a multi-wavelength emission. More importantly, the residual stress and the dislocation density can be suppressed by utilizing the deep-hole pattern and lateral overgrowth, contributing to a lower piezoelectric polarization field and a higher spontaneous emission rate. These ultrafast and high-efficient multi-color micro-LEDs are suitable for the application in high-resolution display, flexible devices, and high-speed visible-light-communication.