O phototransistors with ultrahigh responsivity*

Highly-sensitive and flexible photodetectors are desirable for future optoelectronics. However, lacking of obvious current gain mechanism, the sensitivity of graphene-based photodetectors still can’t compare with traditional PMTs and APDs. Here we report a transfer-free structure of hybrid phototransistor consisting of graphene/Cu₂O QDs. It has an ultrahigh responsivity over 10¹⁰A/Wand fW light detectivity even at room temperature. It demonstatrates excellent flexibility with responsivity still higher than 4×10⁶ A/W. Our results revealed an important QD-graphene base-collector amplification mechanism which mimics the carrier density amplification in usual transistors, only much larger. This mechanism was strongly supported by our quantum capacitance measurements and the inversion relation between the responsivity and the incident power. This mechanism should serve as a guidance for further efforts seeking ultrahigh gain using 2D hybrid structures.