High-performance MoS 2 phototransistors with Hf 1- x Al x O back-gate dielectric layer grown by plasma enhanced atomic layer deposition.

Molybdenum sulfide (MoS 2 ) as an emerging optoelectronic material, shows great potential for phototransistors owing to its atomic thickness, adjustable band gap, and low cost. However, the phototransistors based on MoS 2 have been shown to have some issues such as large gate leakage current, and interfacial scattering, resulting in suboptimal optoelectronic performance. Thus, Al-doped hafnium oxide (Hf 1- x Al x ) is proposed to be a dielectric layer of the MoS 2 -based phototransistor to solve this problem because of the relatively higher crystallization temperature and dielectric constant. Here, a high-performance MoS 2 phototransistor with Hf 1- x Al x O gate dielectric layer grown by plasma-enhanced atomic layer deposition has been fabricated and studied. The results show that the phototransistor exhibits a high responsivity of 2.2 × 10 4 A W -1 , a large detectivity of 1.7 × 10 17 Jones, a great photo-to-dark current ratio of 2.2 × 10 6 %, and a high external quantum efficiency of 4.4 × 10 6 %. The energy band alignment and operating mechanism were further used to clarify the reason for the enhanced MoS 2 phototransistor. The suggested MoS 2 phototransistors could provide promising strategies in further optoelectronic applications.