Improved liquid phase exfoliation technique for the fabrication of MoS₂/graphene heterostructure-based photodetector

2D nanosheets produced using liquid phase exfoliation method offers scalable and cost effective routes to optoelectronics devices. But this technique sometimes yields high defect, low stability, and compromised electronic properties. In this work, we employed an innovative approach that improved the existing liquid phase exfoliation method for fabricating MoS₂/graphene heterostructure-based photodetector with enhanced optoelectronic properties. This technique involves hydrothermally treating MoS₂ before dispersing it in a carefully chosen and environmentally friendly IPA/water solvent for ultrasonication exfoliation through an optomechanical approach. Thereafter, heterostructure nanosheets of MoS₂ and graphene were formed through sequential deposition technique for the fabrication of vertical heterojunctions. Furthermore, we achieved a vertically stacked MoS₂/graphene photodetector and a bare MoS₂ photodetector. The MoS₂/graphene hybrid nanosheets were characterized using spectroscopic and microscopic techniques. The results obtained show the size of the nanosheets is between 350 and 500 nm on average, and their thickness is less than or equal to 5 nm, and high crystallinity in the 2H semiconducting phase. The photocurrent, photoresponsivity, external quantum efficiency (EQE), and specific detectivity of MoS₂/graphene heterostructure at 4 V bias voltage and 650 nm illumination wavelength were 3.55 μA, 39.44 mA/W, 7.54 %, and 2.02 × 10¹⁰ Jones, respectively, and that of MoS₂ photodetector are 0.55 μA, 6.11 mA/W, 1.16 %, and 3.4 × 10⁹ Jones. The results presented indicate that the photoresponse performances of the as-prepared MoS₂/graphene were greatly improved (about 7-fold) compared to the photoresponse of the sole MoS₂. Again, the MoS₂/graphene heterostructure fabricated in this work show better optoelectronic characteristics as compared to the similar heterostructure prepared using the conventional solution processed method. The results provide a modest, inexpensive, and efficient method to fabricate heterojunctions with improved optoelectronic performance.