Intrinsic Photoconductivity of few-layered ZrS2 Phototransistors via Multiterminal Measurements

We report intrinsic photoconductivity studies on one of the least examined layered compounds, ZrS2.Few-atomic layer ZrS2 field-effect transistors were fabricated on the Si/SiO2 substrate and photoconductivity measurements were performed using both two- and four-terminal configurations under the illumination of 532 nm laser source. We measured photocurrent as a function of the incident optical power at several source-drain (bias) voltages. We observe a significantly large photoconductivity when measured in the multiterminal (four-terminal) configuration compared to that in the two-terminal configuration. For an incident optical power of 90 nW, the estimated photosensitivity and the external quantum efficiency (EQE) measured in two-terminal configuration are 0.5 A/W and 120%, respectively, under a bias voltage of 650 mV. Under the same conditions, the four-terminal measurements result in much higher values for both the photoresponsivity (R) and EQE to 6 A/W and 1400%, respectively. This significant improvement in photoresponsivity and EQE in the four-terminal configuration may have been influenced by the reduction of contact resistance at the metal-semiconductor interface, which greatly impacts the carrier mobility of low conducting materials. This suggests that photoconductivity measurements performed through the two-terminal configuration in previous studies on ZrS2 and other 2D materials have severely underestimated the true intrinsic properties of transition metal dichalcogenides and their remarkable potential for optoelectronic applications.

Analysis of NB Josephson Junction Properties under Optical Irradiation

The gap voltage shift of Nb Josephson junctions fabricated on different substrates is measured under optical illumination at several conditions of light intensity and chopping frequency. The signal dependence on the chopping frequency for junctions realized on glass substrates is bolometer-like with a strong thermal coupling between film and substrate. The responsivity of a junction of 50 μ m × 20 μ m is 50 V/W in vacuum and at liquid helium temperature, and its time constant is lower than 10 μ s . The linearity of the response on the optical power extends over five order of magnitude. The response of junctions fabricated on silicon substrates is flat versus the chopping frequency and about 100 times lower than a junction on glass with the same incident optical power. The shift of the gap at temperatures between 1.2 K and 4.2 K has been measured to separate the nonequilibrium effects from the heating effects.