Investigation of multi-color, broadband quantum well infrared photodetectors with digital graded superlattice barrier and linear-graded barrier for long wavelength infrared applications

We report four different InGaAs/AlGaAs multi-color, broadband (BB) quantum well infrared photodetectors (QWIPs) with digital graded superlattice barrier (DGSLB) and linear-graded barrier (LGB) for long wavelength infrared (LWIR) detection. The two DGSLB-QWIPs were grown using compositionally DGSLB structures with GaAs/Al0.15Ga0.85As material system to create a staircase-like band gap variation in the barrier region. A BE spectral response (7-16 mum) was obtained under positive biases while a normal spectral response (lambda (p) = 11 mum) was obtained under negative biases in the BB-DGSLB-QWIP. A high sensitivity double barrier (DB)-DGSLB-QWIP with a thin undoped Al0.15Ga0.85As DB grown on both side of the quantum well has also been studied. A normal spectral response with peak wavelength at 12 mum was obtained in this device under both positive and negative biases. In addition, two InGaAs/AlGaAs QWIPs using AlxGa1-xAs LGB with and without AlGaAs DB layers have also been investigated. For the BB-LGB-QWIP, the BB spectral response was obtained under positive biases while the voltage-tunable multi-color detection with two peaks were obtained at negative biases. A very high responsivity was achieved in the DB-LGB-QWIP. (C) 2001 Published by Elsevier Science B.V.