Very high transmittance, back-illuminated, silicon-on-sapphire semiconductor wafer substrate for high quantum efficiency and high resolution, solid-state, imaging focal plane arrays

摘要

An advanced, very high transmittance, back-illuminated, silicon-on-sapphire wafer substrate design is presented for enabling high quantum efficiency and high resolution, silicon or silicon-germanium avalanche photodiode detector arrays. The wafer substrate incorporates a stacked antireflective bilayer between the sapphire and silicon layers, comprised of single crystal aluminum nitride (AlN) and non-stoichiometric, silicon rich, amorphous silicon nitride (a-SiN_X1.33), that provides optimal refractive index matching between sapphire and silicon. A one quarter wavelength, magnesium fluoride (λ/4-MgF₂) antireflective layer deposited on the back surface of the thinned sapphire provides refractive index matching at the air-sapphire interface. Selecting a composition of x=0.62 for a-SiN_X, tunes an optimal refractive index for the layer. Selecting design thicknesses of 52 nm for single crystal AlN, 30 nm for a-SiN_0.62, and 120 nm for λ/4-MgF₂ yields a back-illuminated optical transmittance T50% for 250-300 nm, T70% for 300-400 nm and T90% for 400-1100 nm.