Low-pressure metalorganic vapor-phase epitaxy growth conditions of AlxGa1−xN epilayers on c-oriented sapphire have been optimized for aluminum mole fractions x lying in the 0–0.35 range both on GaN and AlN nucleation layers, with a view to application in visible blind UV photodetectors. Good structural, electrical, and optical properties were obtained for undoped and n-type doped AlGaN alloys on (0001)-oriented sapphire substrates. A typical full width at half maximum of 670–800 arc s is measured for the (0002) x-ray double-diffraction peak in the ω mode of 1-μm-thick AlGaN epilayers grown on a GaN nucleation layer. Room-temperature electron mobilities up to 90 cm2/V s are measured on n-type (1018 cm−3) AlGaN epilayers. The low-temperature photoluminescence (T=9 K) performed on nonintentionally doped AlGaN epilayers with low-Al content (10% and 14%) exhibits reproducibly a sharp exciton-related peak, associated with two phonon replica and does not exhibit any low-photon energy transitions. Optical transmission as well as absorption coefficient measurements using photothermal deflection spectroscopy have been used to study the variation of the T=300 K energy gap of AlGaN with the aluminum concentration. Visible-blind AlGaN(Si)-based photoconductors and Schottky barrier photodiodes with good operating characteristics have been fabricated with these materials.

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Improved Aluminum-Gallium-Nitride p-i-n photodetectors with different active regions are reported, designed for the measurement of UV-A (315 to 380 nm), UV-B (280 to 315 nm), and UV-C (< 280 nm) radiation. The spectral responsivity of Al x Ga 1-x N photodetectors can be tailored by bandgap engineering of the Al x Ga 1-x N layers and integration of filter layers. Intrinsically visible-blind p-i-n photodetectors are measured on-wafer and packaged in TO-18 headers. Photocurrent measurements in photovoltaic mode result in responsivity values of up to 0.21 A/W for UV-A (EQE = 70 %), 0.14 A/W for UV-B (EQE = 56 %), and 0.11 A/W for UV-C (EQE = 57 %), respectively. Room temperature dark current density values as low as 30 pA/cm² at a reverse bias of -3 V yield a specific detectivity of more than 4×10 14 cmHz 0.5 /W. Response time data of the p-i-n photodiodes indicate a rise time of 1.7 ns and a fall time (1/e) of 4.5 ns. Long term stability tests over 1000 h at an irradiance of 5 W/cm² demonstrate the potential of these photodetectors for demanding applications such as the continuous monitoring of high irradiance ultraviolet light sources. Index Terms-Aluminum gallium nitride, p-i-n diodes, Semiconductor epitaxial layers, Ultraviolet photodetectors. 1077-260X (c)

The current paper focuses on several mechanical aspects of a waferlevel packaging approach using a direct face-to-face Chip-to-Wafer (C2W) bonding of a MEMS device on an ASIC substrate wafer. Requirements of minimized inherent stress from packaging and good decoupling from forces applied in manufacturing and application are discussed with particular attention to the presence of through-silicon vias (TSV) in the substrate wafer. The paper deals with FEM analysis of temperature excursion, pressure during molding, materials used and handling load influence on mechanical stress within the TSV system and on wafer level, which can be large enough to disintegrate the system