LOW DARK CURRENT DUAL-BAND INFRARED PHOTODETECTOR USING THIN ALAS BARRIERS AND GAMMA-X MIXED INTERSUBBAND TRANSITION IN GAAS QUANTUM-WELLS

A low dark current dual band quantum well infrared photodetector is demonstrated by adding thin AlAs barriers to the usual detector structure, which consists of Si-doped GaAs wells separated by thick AlGaAs barriers. The advantages of adding the thin AlAs barriers to clad the quantum wells are that (a) the detector displays a low dark current and (b) intersubband photocurrents result from transitions from both the Gamma ground to the first excited state, and from the Gamma ground to a mixed Gamma-X excited state because the X-valley band edge forms a well in AlAs and intrinsic Gamma-X mixing occurs. The spectral peaks of these two transitions, which occur at 8.5 and 5.5 mu m in our test structure, can be varied by changing device parameters during growth.