Current characteristics of the double-barrier ${\mathrm{Al}}_{0.25}$${\mathrm{Ga}}_{0.75}$As/${\mathrm{Al}}_{0.45}$${\mathrm{Ga}}_{0.55}$As/GaAs single-quantum-well structures

We have calculated the dark current-voltage (I-V) characteristics of the double-barrier (DB) ${\mathrm{Al}}_{0.25}$${\mathrm{Ga}}_{0.75}$As/${\mathrm{Al}}_{0.45}$${\mathrm{Ga}}_{0.55}$As/GaAs single-quantum-well structure used in quantum-well infrared photodetectors (QWIP’s) by varying the ${\mathrm{Al}}_{0.25}$${\mathrm{Ga}}_{0.75}$As and ${\mathrm{Al}}_{0.45}$${\mathrm{Ga}}_{0.55}$As barrier width. Both the three-dimensional injected emitter current and the two-dimensional quantum-well current are evaluated by first calculating the transmission coefficient via the transfer-matrix method with Airy functions as basis wave functions. The two-dimensional density of states of the finite well is evaluated utilizing Green’s functions. The characteristics of a quasibound state are represented by a broad transmission peak as well as a smooth step in the density of states. By varying the barrier width, the low dark current and the high photocurrent in a bound-to-quasibound DB quantum well are compared to the bound-to-bound and bound-to-continuum QWIP’s. We further illustrate the I-V characteristics of the coupled current in which two component currents, emitter and two-dimensional quantum-well current, are comparable.