TRANSPORT MECHANISM OF GAMMA-BAND AND X-BAND ELECTRONS IN ALXGA1-XAS ALAS/GAAS DOUBLE-BARRIER QUANTUM-WELL INFRARED PHOTODETECTORS/

The effect of the Gamma- and X-band electrons in the Al0.25Ga0.75As/Al As/GaAs double-barrier quantum well (DBQW) is investigated by a micros copic empirical pseudopotential calculation. The DBQW structure used i n the calculation is designed as a 3-5-mu m quantum-well infrared phot odetector with an associated transition energy of 313 meV. DBQW tunnel ing transmission via Gamma- and X-like states as a function of electro n energy and applied voltage are described and compared to that in a s ingle-barrier AlAs/GaAs quantum well. The dark current is simulated by the confined ground-state electron tunneling out of the: well. We fin d that, at high-bias voltage, tunneling via X-like states increases th e current by a few orders of magnitude. We have also varied the additi onal barrier thickness and found that for a very thin (<20 Angstrom) a dditional barrier DBQW, the excited-state electrons are not blocked by the Gamma-band barrier, and may give a high photocurrent without the assistance of the X band, although the dark current also increases.