Optical control of the mobility of a MODFET with a layer of self-assembled quantum dots

We report an experimental study of GaAs/Al0.33Ga0.67As modulation doped field effect (MODFET) transistors, in which an InAs layer of self-assembled quantum dots is placed in one of the Al0.33Ga0.67As barrier layers close to the two-dimensional electron gas (2DEG). We find the source–drain resistance is bistable with the two states controlled by illumination and applied gate bias. Brief illumination induces a large, persistent drop in the resistance, which can be recovered by applying a positive gate bias. Magneto-transport measurements show that while illumination causes only a relatively small change in the 2DEG density, it can greatly enhance its mobility. We suggest this is because the 2DEG mobility is limited by percolation of the electrons through the rough electrostatic potential induced by the charged dots. Illumination reduces the negative charge trapped in the dots, thus smoothing the conduction band potential, which produces a large increase in the mobility.