Transport mechanism of Γ- and X-band electrons in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As/AlAs/GaAs double-barrier quantum-well infrared photodetectors

The effect of the Γ- and X-band electrons in the ${\mathrm{Al}}_{0.25}$${\mathrm{Ga}}_{0.75}$As/AlAs/GaAs double-barrier quantum well (DBQW) is investigated by a microscopic empirical pseudopotential calculation. The DBQW structure used in the calculation is designed as a 3–5-μm quantum-well infrared photodetector with an associated transition energy of 313 meV. DBQW tunneling transmission via Γ- and X-like states as a function of electron energy and applied voltage are described and compared to that in a single-barrier AlAs/GaAs quantum well. The dark current is simulated by the confined ground-state electron tunneling out of the well. We find that, at high-bias voltage, tunneling via X-like states increases the current by a few orders of magnitude. We have also varied the additional barrier thickness and found that for a very thin (<20 Å) additional barrier DBQW, the excited-state electrons are not blocked by the Γ-band barrier, and may give a high photocurrent without the assistance of the X band, although the dark current also increases. © 1996 The American Physical Society.