Understanding the physical mechanism behind the laser-induced damage of multilayer dielectric interference coatings is essential for developing ultra-high intensity laser systems. The previous work reported high damage thresholds of MLD mirrors and blister formation near the threshold. Here, we present the cross-sectional study of the blisters using transmission electron microscopy and focused ion-beam processing. The measurement shows evidence of void formation and phase transformation under the surface, interdiffusion, and intermixing at the interfaces. These findings provide valuable insights into the mechanisms behind laser-induced damage, facilitating the development of more robust and reliable optics for high-power laser applications.
Point defects are at the heart of the important properties of wide band-gap and oxide semiconductors for power electronics applications, and therefore understanding the details of point defects and their role in determining the properties becomes imperative. Beta-Ga2O3 has received significant attention recently due to its unique advantages, including high breakdown voltage and availability as bulk substrates, which make it a viable candidate for next-generation power device applications. Here we present the first direct microscopic observation of the formation of interstitial-divacancy complexes within beta-Ga2O3 lattice using atomic resolution scanning transmission electron microscopy. We directly observed that cation atoms are present in multiple interstitial sites, and each interstitial atom is paired with two adjacent vacancies. The observed structure of the complexes is consistent with the calculation using density functional theory (DFT), which predicts them to be compensating acceptors. The number of the observed complexes increase as a function of Sn doping concentration, which matches with the increase in the concentration of the trap state at Ec - 2.1 eV measured using deep level optical spectroscopy, which strongly suggests that the defects corresponds to that trap level. Our finding provides new crucial information on the exact origin of the properties of beta-Ga2O3 that has been unobtainable using other methods. The results also provide new important insight on the material’s unique response to the impurity incorporation that can impact their properties, which can ultimately guide the development of growth and doping of new-generation materials for power electronics.
We report on the design, demonstration and current status of tunnel-injected ultra-violet light emitting diodes (UV LEDs). III-Nitride ultraviolet light emitting diodes (UV LEDs) are promising in various applications including sterilization, water purification and medical sensing. However, both the light extraction efficiency and electrical efficiency face fundamental challenges for the conventional UV LED structures. This stems from the poor p-type conductivity and high p-type contact resistance. Hole injection using interband tunneling provides an elegant solution to the fundamental issues of UV LEDs, and can resolve both the hole injection and light extraction issues that have been the primary problems for UV LEDs. In this talk, we will discuss in detail the heterostructure design and demonstration through polarization engineering to realize efficient interband tunneling in ultra-wide band gap AlGaN material. We will then outline some of the growth and fabrication challenges, and discuss our approaches to overcome these. Finally, we will present our results on tunnel-injected UV LEDs that have enabled us to achieve efficient UV light emission in the UVA and UVB wavelength ranges with on-wafer efficiencies comparable to state-of-the-art values [1,2,3].
References:
1. Yuewei Zhang, et al. ''Interband tunneling for hole injection in III-nitride ultraviolet emitters", Appl. Phys. Lett. 106, 141103 (2015);
2. Yuewei Zhang, et al. "Design of p-type cladding layers for tunnel-injected UV-A light emitting diodes", Appl. Phys. Lett. 109, 191105 (2016);
3. Yuewei Zhang, et al. “Tunnel-injected sub-260 nm ultraviolet light emitting diodes”, Appl. Phys. Lett. 110, 201102 (2017).
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