Tunneling assisted thermionic emission in double-barrier quantum well structures

We report on experimental and theoretical investigations of the dark current behavior in n-type GaAs/AlAs/Al sub0.3 Ga sub0.7 As double-barrier quantum wells (DBQW). The dark current perpendicular to the 50-period DBQW structures shows evidence of tunneling through the 2-nm-wide AlAs tunnel barriers and thermionic emission across the 25-nm-wide AlGaAs layers. The temperature dependence is in good agreement with our numerical simulations, using an effective escape rate of 2.2 x 10 high14 s high-1. The dark current is further modified by internal electric fields caused by an asymmetric dopant distribution, which partially arises from a dopant segregation during epitaxial growth. We also present a theoretical simulation showing how the dark current versus voltage dependence is influenced by these space-charge fields.