CURRENT CHARACTERISTICS OF THE DOUBLE-BARRIER AL0.25GA0.75AS AL0.45GA0.55AS/GAAS SINGLE-QUANTUM-WELL STRUCTURES/

We have calculated the dark current-voltage (I-V) characteristics of t he double-barrier (DB) Al0.25Ga0.75As/Al0.45Ga0.55As/GaAs single-quant um-well structure used in quantum-well infrared photodetectors (QWIP's ) by varying the Al0.25Ga0.75As and Al0.45Ga0.55As barrier width. Both the three-dimensional injected emitter current and the two-dimensiona l quantum-well current are evaluated by first calculating the transmis sion coefficient via the transfer-matrix method with Airy functions as basis wave functions. The two-dimensional density of states of the fi nite well is evaluated utilizing Green's functions. The characteristic s of a quasibound state are represented by a broad transmission peak a s well as a smooth step in the density of states. By varying the barri er 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 bou nd-to-continuum QWIP's, We further illustrate the I-V characteristics of the coupled current in which two component currents, emitter and tw o-dimensional quantum-well current, are comparable.