High-performance MoS₂ phototransistors with Hf_1-x Al _x O back-gate dielectric layer grown by plasma enhanced atomic layer deposition

Molybdenum sulfide (MoS2) 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 MoS2 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 (Hf1-xAlx) is proposed to be a dielectric layer of the MoS2-based phototransistor to solve this problem because of the relatively higher crystallization temperature and dielectric constant. Here, a high-performance MoS2 phototransistor with Hf1-xAlxO 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 x 10(4) A W-1, a large detectivity of 1.7 x 10(17) Jones, a great photo-to-dark current ratio of 2.2 x 10(6)%, and a high external quantum efficiency of 4.4 x 10(6)%. The energy band alignment and operating mechanism were further used to clarify the reason for the enhanced MoS2 phototransistor. The suggested MoS2 phototransistors could provide promising strategies in further optoelectronic applications.