A thin film indium gallium arsenide focal plane array for visible and near infrared hyperspectral imaging

Abstract

Indium gallium arsenide (InGaAs) focal plane arrays (FPAs) have proven useful in a wide variety of scientific, commercial, and military applications ranging from near infrared spectroscopy to night vision imaging. In a two-dimensional InGaAs FPA, an InGaAs photodiode array is hybrid-integrated to a silicon CMOS readout integrated circuit using indium bump-bonding techniques. The array is backside-illuminated with a long wavelength cutoff at 1.7 /spl mu/m due to the bandgap of the In/sub 0.57/Ga/sub 0.53/As active layer and a 0.9 /spl mu/m cut-on due to absorption in the indium phosphide (InP) substrate. We report a novel heteroepitaxial structure and process technology in which a thin (/spl les/ 0.3 /spl mu/m) InP common cathode is inserted under the InGaAs active layer. The InP substrate is removed after the FPA has been hybrid-integrated. The result is a thin (< 5 /spl mu/m) photodiode array membrane supported on a two-dimensional matrix of indium columns. The FPA exhibits photoresponse from 0.5 /spl mu/m in the visible to the 1.7 /spl mu/m InGaAs cutoff and is ideal for broad-band imaging spectroscopy or hyperspectral imaging.