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. (C) 2003 MAIK "Nauka / Interperiodica".