Dopant Migration-Induced Interface Dipole Effect in n-Doped GaAs/AlGaAs Terahertz Detectors

A heterojunction interfacial workfunction internal photoemission (HEIWIP) terahertz detector with $\sim\!\!\hbox{1}\!\times\!\hbox{10}^{18}\ \hbox{cm}^{-3}$ n-type doped GaAs emitters in a multilayer $\hbox{GaAs/Al}_{0.13}\hbox{Ga}_{0.87} \hbox{As}$ heterostructure is presented. The detection mechanism is based on free carrier absorption with a broad response extending to $\sim$5.26 THz (57 $\mu\hbox{m}$), corresponding to an effective workfunction of $\sim$21.8 meV, which is much smaller than the offset expected for an Al fraction of $x = \hbox{0.13}$ at a $\hbox{1} \times \hbox{10}^{18}\ \hbox{cm}^{-3}$ doping. This is attributed to a reduction of the conduction band offset by interface dipole formation between the accumulated negative charges at the interface states and migrated positively charged donors in the barrier. The device has a peak responsivity of 0.32 A/W at $\sim\!\!\hbox{26}\ \mu\hbox{m}$ at 5 K. It is demonstrated that the dopant migration-induced interface dipole effect can be used to extend the zero response threshold frequency $(f_{0})$ of n-type HEIWIP detectors.