Quantum-well infrared photodetectors with digital graded superlattice barrier for long-wavelength and broadband detection

We report two high-performance quantum-well infrared photodetectors (QWIPs) using GaAs/AlGaAs digital graded superlattice barriers and InGaAs quantum wells for long-wavelength infrared and broadband (BB) detection. The compos itionally digital graded superlattice barriers (DGSLBs) of the QWIP structu res were grown using GaAs/AlGaAs digital graded superlattices to form a sta ircase-like composition-graded barrier layer without adjustment of the sour ce temperature (510 degrees C) and the AlGaAs composition (15% Al). In the BB DGSLB QWIP, a broad spectral response from 7 to 16 mu m wavelength range was obtained under positive bias condition, while a normal spectral respon se with peak wavelength at 11 mu m was obtained under the negative bias con dition. In addition, a double-barrier (DB) DGSLB QWIP structure adding a th in (20 Angstrom) undoped Al0.15Ga0.85As on each side of the InGaAs quantum well to form a DB structure for the confinement of electron wave functions in the E-4 states was also studied. A peak responsivity of 3 A/W was obtain ed at V-b = 1 V, T = 35 K, and lambda(p) = 12 mu m, and normal spectral res ponse was observed in this device. (C) 1999 American Institute of Physics. [S0003-6951(99)03842-5].