Comparison of photoresponse of transistors based on graphene-quantum dot hybrids with layered and bulk heterojunctions

Phototransistors based on graphene–quantum dot hybrids have a high responsivity and gain. However, the influence of the type of heterojunction on the photoresponse of the transistors is still undetermined. A comparison was performed on field-effect phototransistors (FEpTs) with two types of heterojunctions: layered heterojunctions (LHs) and bulk heterojunctions (BHs). Through a comparative study, it was shown that BH–FEpTs had electron and hole mobilities (μ_E and μ_H) of 677 and 527 cm² V⁻¹ s⁻¹ whereas LH–FEpTs had lower mobilities of μ_E = 314 cm² V⁻¹ s⁻¹ and μ_H = 367 cm² V⁻¹ s⁻¹. The large interfacial area in the BHs reduced the degree of channel order (α) by two orders of magnitude compared with the LHs. Although a higher mobility was achieved, an increase in the degree of channel disorder and the lack of an effective transfer mechanism limits the responsivity in BH–FEpTs. Therefore, LH–FEpTs are more appropriate candidates for near infrared phototransistors. (paper)