Transition in (001) AlGaAs/AlAs/GaAs double-barrier quantum structure for infrared photodetection

Optical transitions for the (001) Al_0.3Ga_0.7As/AlAs/GaAs double-barrier superlattices are evaluated by a semiempirical, tight-binding calculation. The oscillator strength between the hole and electron states confined in either Γ- or X-like well are investigated as a function of AlAs slab thickness. Intersub-band transition within the conduction band, including Γ- and X-like superlattice (SL) states, is described for a quantum well infrared photodetector (QWIP). We found that for a specific design structure, it is possible to achieve the dual wavelength QWIP with comparable oscillator strength for the 3-5 μm and 8-14 μm atmospheric windows. In addition, by varying the AlAs barrier thickness, the characteristics of bound-to-continuous and bound-to-quasibound QWIPs are related to the stationary discrete SL states. As the AlAs thickness increases, the bound-to-continuous state transition becomes weak while the bound-to-quasibound state transition becomes more significant. Optical coupling between X-like state is relatively weak and the transition between the different characteristic states is even weaker.