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Heteroepitaxial crystallographic tilt has been investigated as a possible strain‐relief mechanism in Al‐rich (Al>50%) AlGaN heteroepitaxial layers grown on single‐crystal (0001) AlN substrates with varying miscuts from 0.05° to 4.30°. The magnitude of the elastic lattice deformation‐induced tilt increases monotonically with the miscut angle, tightly following the Nagai tilt model. Although tilt angles as high as 0.1° are recorded, reciprocal space mapping (RSM) broadening and wafer bow measurements do not show any significant changes as a function of the heteroepitaxial tilt angle. While crystallographic tilting has been shown to be effective in controlling strain in some other heteroepitaxial systems, it does not provide any appreciable strain relief of the compressive strain in AlGaN/AlN heteroepitaxy. [ABSTRACT FROM AUTHOR]

Herein, Al‐rich AlGaN‐based avalanche photodiodes (APDs) grown on single crystal AlN substrates high ultraviolet‐C sensitivity for λ < 200 nm are fabricated, while exhibiting blindness to λ > 250 nm. A maximum quantum efficiency of 68% and peak gain of 320 000 are estimated resulting in a figure of merit of ≈220 000 in devices with ϕ = 100 μm. As expected, a decrease in gain with increase in device size is observed and a gain of ≈20 000 is estimated in devices with ϕ = 400 μm. Overall, two orders of magnitude higher performance are observed in APDs on single crystal AlN substrates compared to those on sapphire. [ABSTRACT FROM AUTHOR]

AlGaN lateral polarity structures (LPS) with varying Al composition, have been fabricated by metalorganic chemical vapour deposition on LPS templates containing µm size domains. III-metal and N-polar AlGaN domains have been grown on LT-AlN and c-sapphire domains, respectively. LPS characterization by SEM and AFM reveals two major effects when the Al composition has been varied: (a) A high Al content leads to columnar growth within N-polar domains and (b) a height difference between the polar domains can be observed for low Al compositions towards III-polarity. The surface quality of the III-polar domains is not effected by the Al composition. The surface roughness of N-polar domains decreases for lower Al compositions. The high periodicity of the polar domains and the high quality of the boundary between domains suggest a high potential of AlGaN LPS to be used as lateral wave guides for quasi phase matching. [ABSTRACT FROM AUTHOR]

Growth and characterization of AlN based lateral polarity structures (LPS) are presented. The LPS were grown by MOCVD using patterned low temperature AlN/sapphire substrates: the Al-polar and N-polar AlN grew on AlN buffer layer and nitrided sapphire, respectively. AFM images showed a height difference between the two adjacent domains of different polarity on the order of 30 nm, which was equivalent to the low temperature AlN buffer layer thickness. SEM images provided an insight in the growth mode of the two polarities. It was shown that Al-polar AlN grew two-dimensionally, leading to a smooth well coalesced layer, while N-polar AlN grew primarily three-dimensionally, leading to a columnar structure. This difference in the growth mode led to different properties of domains with opposite polarity, including strain and defect incorporation, as observed by X-ray diffraction, photoluminescence, and Raman spectroscopy measurements. Finally, an outlook on the applicability and future development of AlN-based LPS is given. (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [ABSTRACT FROM AUTHOR]