Prof. Wei Guo
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences,China
Speech Tilte: Polarity control of
III-nitride and approaches in the development of high efficiency AlGaN-based deep
Abstract: AlGaN based deep ultraviolet light-emitting-diodes (DUV-LED) have attracted numerous attentions in the application of UV disinfection, and NLOS communication. However, the development of AlGaN-based UV-LED is still in its infancy compared to InGaN-based blue and green LEDs owning to varies scientific and technical challenges including poor crystalline quality, strong quantum-confined-stark-effect, and UV absorption by p-GaN and metal contact.
In this talk, we first discuss our recent progress on DUV-LEDs grown miscut sapphire substrates. High internal quantum efficiency as high as 92% was demonstrated, thanks to Al and Ga phase separations and consequently carrier localization effect in the active region. The correlation between micro-scale current distribution and surface morphology was provided, suggesting that current prefer to flow through the step edges of the epitaxial layers under low injection current. Furthermore, ECCI images and cross-sectional TEM indicate that Ga-rich stripes are not associated with underlying threading dislocations, therefore poses no damages to the stability of UV-LEDs.
Secondly, we will discuss the influence of polarity control and existence of “inversion domain boundaries” in the electroluminescence property of DUV-LEDs. A “lateral-polarity-structure” (LPS) is proposed, where III- and N-polar domains were grown simultaneously side-by-side on a single wafer. After inserting an AlGaN/AlN superlattice and V/III ratio modification during growth, the surface morphology of N-polar domain is greatly improved, leading to a single peak emission at wavelength of 275 nm in both III and N-polar domains, and 10-fold stronger peak intensity at the inversion domain boundary. The existing of nanoscale “inversion domain” was also discovered in AlN thin film as revealed by HR-TEM. Surprisingly, these inversion domains are fully eliminated after high temperature thermal annealing, suggesting that thermal treatment is an ideal approach in recover the crystalline quality of AlN and benefits the fabrication of DUV-LEDs.
Prof. Wei Guo received PhD degree from North Carolina State University. He then joined Advanced Materials Inc. as a research engineer, focusing on process development of cutting-edge Sym3 TM ICP etching equipment. Prof. Guo joined Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences in 2016, His current research interests include AlGaN thin film growth, development of UV-LEDs/ UV-Photodetectors, and GaN-based HEMT devices. Current achievements are: 1) Initiate the research on “lateral-polarity-structure” UV-LED with significantly enhanced light emission, and development of the hypothesis of 3D band diagram which can be widely used in III-nitride community; 2) Utilize MOCVD growth optimization and offcut angle modulation, obtain a record-high IQE value of 92% and EQE value > 3.7% in DUV wavelength region; 3) Development of self-powered UV photodetectors and self-isolated GaN HEMT devices with polarity control scheme. Prof. Guo has published more than 50 journal articles with citations higher than 1000.