THE EFFECT OF BARRIER STRUCTURE ON THE PERFORMANCE OF DOUBLE-BARRIER QUANTUM-WELL INFRARED PHOTODETECTORS

The effects of the inner and outer barriers on the performance of mid- wavelength (3-5 mu m) GaAs/AlGaAs double barrier quantum well infra-re d photodetectors (DBQWIPs) have been studied. It was found that the pe ak response wavelength had a significant red shift when the thickness of the AlAs inner barriers was below 10 Angstrom. This is attributed t o the lowering of the upper state energy in the quantum wells. The res ponsivity of DBQWIPs decreases with the inner barrier thickness. This is because the optical gain decreases faster than the increasing rate of the quantum efficiency when the inner barrier thickness increases. The responsivities for devices with different Al compositions (0.35 an d 0.24) in the outer barriers are in the same range, but the dark curr ents for devices with Al(0.35)G(0.65)As outer barriers are much lower than those with Al0.24Ga0.76As outer barriers. Nearly two orders of ma gnitude improvement in detectivity was observed when the Al compositio n in the outer barriers was changed from 0.24 to 0.35. A high detectiv ity of 1 x 10(11) cm Hz(1/2) W-1 at 77 K was obtained for a device wit h 12 Angstrom AlAs inner barriers and 300 Angstrom Al0.35Ga0.65As oute r barriers.