Mixed‐Dimensional MoS₂/Ge Heterostructure Junction Field‐Effect Transistors for Logic Operation and Photodetection

Abstract There has been a growing interest in electronic and optoelectronic devices based on heterostructures between atomically thin 2D and 3D semiconductor materials. This paper proposes a 2D molybdenum disulfide (MoS₂)/3D germanium (Ge) junction field‐effect transistor (JFET). Typical electrical characteristics of the JFET are observed, with a low subthreshold swing of ≈88 mV/dec and a high on/off ratio of ≈10⁵. The device exhibits a bidirection photoresponse in which the photocurrent polarity is reversed depending on the wavelength of light. Under visible illumination at 532 nm, the positive photoresponsivity of this device can be modulated by the gate voltage, reaching a peak value of 66 A W⁻¹. In contrast, the device exhibits a tunable negative photoresponse behavior under an infrared illumination of 1550 nm. This is attributed to the competition between the negative photoresponse from the bolometric effect in MoS₂ and the positive photoresponse from photogenerated carriers in Ge. Based on these interesting characteristics in this JFET, three controllable current states (−1, 0, and 1) are realized by changing the gate voltage and infrared light. These results indicate that the device has promising potential as a multifunctional optoelectronic unit, including signal amplification, broadband photodetection, and multilogic calculations.