Low-power driven broadband phototransistor with a PbS/IGO/HfO2 stack

Abstract

Broadband phototransistors have attracted considerable attention for numerous applications. Transistors based on amorphous oxide semiconductors (AOSs) provide an excellent photosensor platform because of the reasonably high mobility, extremely low off-state current, low-cost fabrication capability, and large-area scalability of AOSs. To create photo-responsivity for visible to near-infrared (NIR) light in an AOS transistor, lead sulfide quantum dots (PbS QDs) with a cutoff wavelength of 1300 nm were incorporated using a spin-coating process. The distance between PbS QDs was tailored by short tetrabutylammonium iodide ligands through a ligand exchange process. To reduce the operation voltage of the AOS phototransistor, indium gallium oxide (IGO) and hafnium oxide (HfO₂) films were used as the semiconducting n-type channel and gate insulator, respectively. The IGO and HfO₂ films were grown by plasma-enhanced atomic layer deposition (PEALD). The fabricated PbS QD/IGO phototransistors with an HfO₂ gate insulator exhibited remarkable switching properties, such as a high carrier mobility of 20.1 cm² (V⁻¹ s⁻¹), a low subthreshold gate swing of 0.060 V decade⁻¹, and a high I_ON/OFF ratio of 2.2 × 10⁸. Additionally, they also exhibited a photo-responsivity of 211 A W⁻¹ and a detectivity of 8.9 × 10¹¹ Jones at 1300 nm even at an ultralow power operation (V_GS = ±1 V, V_DS = 0.1 V). Moreover, the fabricated devices showed a reasonable uniformity with near-zero V_TH in different batches and exhibited the modest degradation after the storage of 15 days to air atmosphere even though they were not encapsulated by a suitable passivation layer. The relevant physical rationale is discussed based on structural, optical, and electrical analyses. The results suggest that a phototransistor with a PbS QD/IGO/HfO₂ stack can provide large-area scalable and low-voltage operation routes for visible to NIR imaging, communication, and sensing applications.