2021, van Deurzen, Len, Gómez Ruiz, Mikel, Lee, Kevin, Turski, Henryk, Bharadwaj, Shyam, Page, Ryan, Protasenko, Vladimir, Xing, Huili (Grace), Lähnemann, Jonas, Jena, Debdeep

This report classifies emission inhomogeneities that manifest in InGaN quantum well blue light-emitting diodes grown by plasma-assisted molecular beam epitaxy on free-standing GaN substrates. By a combination of spatially resolved electroluminescence and cathodoluminescence measurements, atomic force microscopy, scanning electron microscopy and hot wet potassium hydroxide etching, the identified inhomogeneities are found to fall in four categories. Labeled here as type I through IV, they are distinguishable by their size, density, energy, intensity, radiative and electronic characteristics and chemical etch pits which correlates them with dislocations. Type I exhibits a blueshift of about 120 meV for the InGaN quantum well emission attributed to a perturbation of the active region, which is related to indium droplets that form on the surface in the metal-rich InGaN growth condition. Specifically, we attribute the blueshift to a decreased growth rate of and indium incorporation in the InGaN quantum wells underneath the droplet which is postulated to be the result of reduced incorporated N species due to increased N2 formation. The location of droplets are correlated with mixed type dislocations for type I defects. Types II through IV are due to screw dislocations, edge dislocations, and dislocation bunching, respectively, and form dark spots due to leakage current and nonradiative recombination.

2020, Amano, Hiroshi, Collazo, Ramón, De Santi, Carlo, Einfeldt, Sven, Funato, Mitsuru, Glaab, Johannes, Hagedorn, Sylvia, Hirano, Akira, Hirayama, Hideki, Ishii, Ryota, Kashima, Yukio, Kawakami, Yoichi, Kirste, Ronny, Kneissl, Michael, Martin, Robert, Mehnke, Frank, Meneghini, Matteo, Ougazzaden, Abdallah, Parbrook, Peter J., Rajan, Siddharth, Reddy, Pramod, Römer, Friedhard, Friedhard, Jan, Sarkar, Biplab, Scholz, Ferdinand, Schowalter, Leo J, Shields, Philip, Sitar, Zlatko, Sulmoni, Luca, Wang, Tao, Wernicke, Tim, Weyers, Markus, Witzigmann, Bernd, Wu, Yuh-Renn, Wunderer, Thomas, Zhang, Yuewei

Solid state UV emitters have many advantages over conventional UV sources. The (Al,In,Ga)N material system is best suited to produce LEDs and laser diodes from 400 nm down to 210 nm - due to its large and tuneable direct band gap, n- and p-doping capability up to the largest bandgap material AlN and a growth and fabrication technology compatible with the current visible InGaN-based LED production. However AlGaN based UV-emitters still suffer from numerous challenges compared to their visible counterparts that become most obvious by consideration of their light output power, operation voltage and long term stability. Most of these challenges are related to the large bandgap of the materials. However, the development since the first realization of UV electroluminescence in the 1970s shows that an improvement in understanding and technology allows the performance of UV emitters to be pushed far beyond the current state. One example is the very recent realization of edge emitting laser diodes emitting in the UVC at 271.8 nm and in the UVB spectral range at 298 nm. This roadmap summarizes the current state of the art for the most important aspects of UV emitters, their challenges and provides an outlook for future developments. © 2020 IOP Publishing Ltd.

2016, Pristovsek, Markus, Han, Yisong, Zhu, Tongtong, Oehler, Fabrice, Tang, Fengzai, Oliver, Rachel A., Humphreys, Colin J., Tytko, Darius, Choi, Pyuck-Pa, Raabe, Dierk, Brunner, Frank, Weyers, Markus

We benchmarked growth, microstructure and photo luminescence (PL) of (112-2) InGaN quantum wells (QWs) against (0001) and (112-0). In incorporation, growth rate and the critical thickness of (112-2) QWs are slightly lower than (0001) QWs, while the In incorporation on (112-0) is reduced by a factor of three. A small step-bunching causes slight fluctuations of the emission wavelength. Transmission electron microscopy as well as atom probe tomography (APT) found very flat interfaces with little In segregation even for 20% In content. APT frequency distribution analysis revealed some deviation from a random InGaN alloy, but not as severe as for (112-0). The slight deviation of (112-2) QWs from an ideal random alloy did not broaden the 300 K PL, the line widths were similar for (112-2) and (0001) while (112-0) QWs were broader. Despite the high structural quality and narrow PL, the integrated PL signal at 300 K was about 4 lower on (112-2) and more than 10 lower on (112-0).