Multiheterojunction Phototransistors Based on Graphene-PbSe Quantum Dot Hybrids

Graphene-semiconductor quantum dot (QD) hybrid field effect phototransistors (FEpTs) have attracted much interest due to their ultrahigh gain and responsivity in photo detection. However, most reported results are based on single-layer heterojunction, and the multiheterojunction FEpTs are often ignored. Here, we design two typical multiheterojunction FEpTs based on graphene-PbSe quantum dot (QD) hybrids, including QD at the bottom layer (QD-bottom) and graphene at the bottom layer (G-bottom) FEpTs. Through a comparative study, G-bottom FEpTs showed a multisaturation behavior due to the multigraphene layer effect, which was absent in the QD-bottom FEpTs. The mobilities for electrons and holes were mu(E) = 147 cm(2) V-1 s(-1) and mu(E) = 137 cm(2) V-1 s(-1) in the G-bottom FEpTs and mu(E) = 14 cm(2) s(-1) and mu(E) = 59 cm(2) V-1 s(-1) in the QD-bottom FEpTs. Higher responsivity (similar to 10(6) A W-1) and faster response rate were both achieved by the G-bottom FEpTs. All of the advantages in G-bottom FEpTs were attributed to the back-gate effect. Therefore, high performance is expected in those FEpTs whose heterojunctions are designed to be close to the back-gate.