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  1. Multimode lasing at sub-300 nm wavelengths is demonstrated by optical pumping in AlGaN heterostructures grown on single-crystal AlN substrates by plasma-assisted molecular beam epitaxy. Edge-emitting ridge-based Fabry–Pérot cavities are fabricated with the epitaxial AlN/AlGaN double heterostructure by a combined inductively coupled plasma reactive ion etch and tetramethylammonium hydroxide etch. The emitters exhibit peak gain at 284 nm and modal linewidths on the order of 0.1 nm at room temperature. The applied growth technique and its chemical and heterostructural design characteristics offer certain unique capabilities toward further development of electrically injected AlGaN laser diodes.
    Free, publicly-accessible full text available March 1, 2023
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  3. We determine the composition dependence of the transverse and longitudinal optical infrared-active phonon modes in rhombohedral α-(Al x Ga 1− x ) 2 O 3 alloys by far-infrared and infrared generalized spectroscopic ellipsometry. Single-crystalline high quality undoped thin-films grown on m-plane oriented α-Al 2 O 3 substrates with x =  0.18, 0.37, and 0.54 were investigated. A single mode behavior is observed for all phonon modes, i.e., their frequencies shift gradually between the equivalent phonon modes of the isostructural binary parent compounds. We also provide physical model line shape functions for the anisotropic dielectric functions. We use the anisotropic high-frequency dielectricmore »constants for polarizations parallel and perpendicular to the lattice c axis measured recently by Hilfiker et al. [Appl. Phys. Lett. 119, 092103 (2021)], and we determine the anisotropic static dielectric constants using the Lyddane–Sachs–Teller relation. The static dielectric constants can be approximated by linear relationships between those of α-Ga 2 O 3 and α-Al 2 O 3 . The optical phonon modes and static dielectric constants will become useful for device design and free charge carrier characterization using optical techniques.« less
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  4. Epitaxial Sc x Al 1− x N thin films of ∼100 nm thickness grown on metal polar GaN substrates are found to exhibit significantly enhanced relative dielectric permittivity (ε r ) values relative to AlN. ε r values of ∼17–21 for Sc mole fractions of 17%–25% ( x = 0.17–0.25) measured electrically by capacitance–voltage measurements indicate that Sc x Al 1− x N has the largest relative dielectric permittivity of any existing nitride material. Since epitaxial Sc x Al 1− x N layers deposited on GaN also exhibit large polarization discontinuity, the heterojunction can exploit the in situ high-K dielectric property to extendmore »transistor operation for power electronics and high-speed microwave applications.« less
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  6. Abstract Harnessing resonant tunneling transport in III-nitride semiconductors to boost the operating frequencies of electronic and photonic devices, requires a thorough understanding of the mechanisms that limit coherent tunneling injection. Towards this goal, we present a concerted experimental and theoretical study that elucidates the impact of the collector doping setback on the quantum transport characteristics of GaN/AlN resonant tunneling diodes (RTDs). Employing our analytical model for polar RTDs, we quantify the width of the resonant-tunneling line shape, demonstrating that the setback helps preserve coherent injection. This design results in consistently higher peak-to-valley-current ratios (PVCRs), obtaining a maximum PVCR = 2.01more »at cryogenic temperatures.« less
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