Polarity-Tunable Field Effect Phototransistors

Field-effect phototransistors feature gate voltage modulation, allowing dynamic performance control and significant signal amplification. A field-effect phototransistor can be designed to be inherently either unipolar or ambipolar in its response. However, conventionally, once a field-effect phototransistor has been fabricated, its polarity cannot be changed. Herein, a polarity-tunable field-effect phototransistor based on a graphene/ultrathin Al₂O₃/Si structure is demonstrated. Light can modulate the gating effect of the device and change the transfer characteristic curve from unipolar to ambipolar. This photoswitching in turn produces a significantly improved photocurrent signal. The introduction of an ultrathin Al₂O₃ interlayer also enables the phototransistor to achieve a responsivity in excess of 10⁵ A/W, a 3 dB bandwidth of 100 kHz, a gain-bandwidth product of 9.14 × 10¹⁰ s^-1, and a specific detectivity of 1.91 × 10¹³ Jones. This device architecture enables the gain-bandwidth trade-off in current field-effect phototransistors to be overcome, demonstrating the feasibility of simultaneous high-gain and fast-response photodetection.