Thermal dissipation enhancement in flip-chip bonded uni-traveling carrier photodiodes.

The thermal properties of modified uni-traveling carrier (MUTC) photodiode flip-chip bonded to AlN and diamond are simulated. The thermal impedance of InGaAs is the primary source of internal heating. An n-down epitaxial structure is designed to improve thermal dissipation. Compared to the conventional p-down configuration, the n-down MUTCs bonded to diamond, or AlN submounts achieved 145% and 110% improvement in dissipated power density at thermal failure, respectively. The improved thermal characteristics presage higher RF output power before thermal failure.

Cavity-based aluminum nanohole arrays with tunable infrared resonances.

This work details the successful computational design, fabrication, and characterization of a cavity-based aluminum nanohole array. The designs incorporate arrays of aluminum nanoholes that are patterned on a dielectric-coated (SiO2 or ZnSe) aluminum base mirror plane. This architecture provided a means of exploring the coupling of the localized resonances, exhibited by the aluminum nanohole array, with the cavity resonance that is generated within the dielectric spacer layer, which resides between the base plane mirror and the nanohole array. Rigorous coupled wave analysis (RCWA) was first used to computationally design the structures. Next, a range of lithographic techniques, including photolithography, E-beam lithography, and nanosphere lithography, were used to fabricate the structures. Finally, infrared spectroscopy and scanning electron microscopy (SEM) were used to characterize the spectral and structural properties of the multilayered devices, respectively. The overall goal of this study was to demonstrate our ability to design and fabricate aluminum-based structures with tunable resonances throughout the infrared region, i.e. from the short-wave through longwave infrared regions of the electromagnetic spectrum (1.5 -12 µm).

Multiband absorbers for the long-wave infrared regime.

We present the development of a long-wave infrared regime multiband absorption filter with simultaneous wavelength and intensity selectivity. The approach employs a technique we call "spectral dithering" to place single-band absorbing pixels across a unit cell such that their weighted sum describes a multiband absorption spectrum. The number of absorption bands is proportional to the number of unique pixels present. Pixel patterning controls wavelength selectivity, whereas pixel distribution controls intensity selectivity. Using the rigorous coupled-wave method for modelling, a filter with three absorption bands between 6 and 14 µm is designed using the spectral dithering technique. The device is fabricated and experimentally verified using Fourier-transform infrared spectroscopy.