Electron transport in unipolar heterostructure transistors with quantum dots in strong electric fields

A model for the explaining specific features of the electron transport in strong electric fields in the quantum-dot unipolar heterostructure transistor (AlGaAs/GaAs/InAs/GaAs/InAs) is presented. It is shown that the two-step shape of the output current-voltage characteristic I _D (V _D ) and the anomalous dependence of the drain current I _D on the gate voltage V _G are caused by the ionization of quantum dots in the strong electric field at the drain gate edge. The ionization of quantum dots sets in at the drain voltage V _D that exceeds the V_D1 value, at which the I _D (V _D ) dependence is saturated (the first step of the I-V characteristic). With the subsequent increase in V _D , i.e., for V _D >V_D1, the I _D (V _D ) dependence has a second abrupt rise due to the ionization of quantum dots, and then, for V _D =V_D2>V_D1, the current I _D is saturated for the second time (the second step in the current-voltage characteristic). It is suggested to use this phenomenon for the determining the population of quantum dots with electrons. The model presented also describes the twice-repeated variation in the sign of transconductance g _m =dI _D /dV _G as a function of V _G .