A transistor and memory operation of a new AlGaAs/InGaAs heterojunction field-effect transistor (HFET) in a tetrahedral-shaped recess (TSR) on the (lll)B GaAs substrate was investigated at a temperature up to 120 K. The TSR-FET memory has a channel on the (lll)A side surfaces of the recess and a single floating quantum dot (QD) gate at the bottom. Owing to the particular shape of the TSR structure, the charge in the floating QD gate can effectively modulate the channel current. We found a clear hysteresis in the current-voltage (I-V) characteristics with an abrupt increase and decrease in the current at the subthreshold gate bias region. Random telegraph signals with a constant amplitude of about 70 nA were also observed in the memory retention characteristics. These phenomena were considered to be attributed to the current modulation by hole charging/discharging in the QD.
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