Interlayer-Exciton Based Nonvolatile Valleytronic Memory

Abstract

Analogous to conventional charge-based electronics, valleytronics aims at encoding data via valley degree of freedom, enabling new routes for information processing. Long-lived interlayer excitons (IXs) in van der Waals heterostructures (HSs) stacked by transition metal dichalcogenides (TMDs) carry valley-polarized information and thus would find promising applications in valleytronic devices. Although great progress of IX based valleytronic devices has been achieved, nonvolatile valleytronic memories are still challenging. Here, we demonstrate IX based nonvolatile valleytronic memory in a WS2/WSe2 HS. The emission characteristics of IX exhibit a large excitonic/valleytronic hysteresis upon cyclic-voltage sweeping. Importantly, IX emission can be electrically switched between a bright state and a dark state with large light-intensity and helicity contrast of about 1.7 and 1.8, respectively, which can be ascribed to the chemical-doping of O2/H2O redox couple between TMDs and substrate. Taking advantage of the large hysteresis, IX can be utilized for manipulating and nonvolatile storing valley information and IX based nonvolatile valleytronic memory has been successfully demonstrated. These findings open up an avenue for nonvolatile valleytronic memory and would motivate more investigations on valleytronic devices.

Room‐Temperature Exciton‐Based Optoelectronic Switch

“…The chemical doping effect of O 2 /H 2 O in monolayer WSe 2 has been observed and experimentally confirmed in van der Waals HSs in our previous work. [34] To verify the above hypothesis, we have performed gatedependent PL measurements of WSe 2 /Au and WSe 2 /SiO 2 at 78 K, because the emission peak of trions is much stronger at low temperature. As shown in Figure 2c and Figure S1a (Supporting Information), two emission peaks emerge at about 1.73 and 1.69 eV at 0 V. The higher energy peak can be attributed to the emission of neutral exciton (X 0 ), which is blueshifted for about 70 meV in comparison to that of room temperature because of lattice contraction at low temperature.…”

“…We also note that the PL intensity changes dynamically during the application of ±60 V biases, this is probably due to charge variations in WSe 2 induced by electrical gating. [34] The slow changes in PL emission might be due to charge trapping and detrapping process caused by defects in WSe 2 . [37] To prove the reproducibility and universality of this strategy, we have fabricated another device with Pt electrodes, which exhibits the same behaviors as described above (Figure S3, Supporting Information).…”