GaN Based UV Sensors for Earth Resources Management, Phase II

This work represents the exploitation of a unique method of crystal growth -- constrained epitaxy (CE) -- in the manufacture of low-noise, multi-color UV sensors. The sensors developed here are based on the GaN/AlGaN materials system and are sensitive in the wavelength range from 250-400nm. Target responsivities are > 0.1 A/W throughout the spectral interest range. The first arrays produced under phase 1 were sensitive both to 285 and 315 nm simultaneously. Multicolor sensitivity improves background noise rejection and provides much more detailed analysis of atmospheric aerosol scattering. Noise is dominated by diode reverse leakage and is less than 10-9A/cm2. The CE manufacturing process is enabled by the recognition that surfaces on which radiation sensitive materials are grown cannot be exposed to plasma etch effluents. To overcome this limitation, a dielectric lift-off-lithography process was developed. In this process, the growth surfaces only come in contact with organic solvents and photosensitive plastics during manufacture. Initial results were obtained on a 10 x 10 diode array. In subsequent work, we intend to produce 100 x 100 arrays. In addition, it the range of attainable spectral sensitivities will be mapped out by studying the range of achievable AlGaN stoichiometries that are practically attainable. More »