Modulating Charge Separation with Hexagonal Boron Nitride Mediation in Vertical Van der Waals Heterostructures

Abstract

Tuning the optical and electrical properties by stacking different layers of two-dimensional (2D) materials enables us to create unusual physical phenomena. Here, we demonstrate an alternative approach to enhance charge separation and alter physical properties in van der Waals heterojunctions with type-II band alignment by using thin dielectric spacers. To illustrate our working principle, we implement a hexagonal boron nitride (h-BN) sieve layer in between an InSe/GeS heterojunction. The optical transitions at the junctions studied by photoluminescence and the ultrafast pump–probe technique show quenching of emission without h-BN layers exhibiting an indirect recombination process. This quenching effect due to strong interlayer coupling was confirmed with Raman spectroscopic studies. In contrast, h-BN layers in between InSe and GeS show strong enhancement in emission, giving another degree of freedom to tune the heterojunction property. The two-terminal photoresponse study supports the argument by showing a large photocurrent density for an InSe/h-BN/GeS device by avoiding interlayer charge recombination. The enhanced charge separation with h-BN mediation manifests a photoresponsivity and detectivity of 9 × 102 A W–1 and 3.4 × 1014 Jones, respectively. Moreover, a photogain of 1.7 × 103 shows a high detection of electrons for the incident photons. Interestingly, the photovoltaic short-circuit current is switched from positive to negative, whereas the open-circuit voltage changes from negative to positive. Our proposed enhancement of charge separation with 2D-insulator mediation, therefore, provides a useful route to manipulate the physical properties of heterostructures and for the future development of high-performance optoelectronic devices.

A Bi-Anti-Ambipolar Field Effect Transistor

“…The InSe region shows strong vibrational peaks at 115, 178, and 228 cm −1 , corresponding to out-of-plane A 1 1g , in-plane E 2 1g, and out-of-plane A 2 1g modes, as reported previously. 15,16 The WSe 2 region exhibits a broad peak at 250 cm −1 , a combination of E 1 2g and A 1g modes, and the characteristic of the few-layered WSe 2 , and the small peak at 302 cm −1 corresponds to the B 1 2g mode. 17 The overlapped InSe/WSe 2 region exhibits all the prominent peaks of InSe and WSe 2 , but the intensity is quenched due to interlayer coupling.…”

“…Here, P is the incident laser power density and A is the active area of the InSe/WSe 2 device. 15,28,33 This enhancement of responsivity under reverse bias is due to the added potential created by the application of strain that efficiently separates the photogenerated electron−hole pairs (Figures S9 and 4g). Therefore, we observe a systematic increase in the photoresponsivity as the applied strain increases (reverse bias in Figure 4e,f).…”

Highly Efficient Photodetection in Metal Nanocluster/Graphene Heterojunctions

“…The performance of the GSH-Au NCs photodetector was determined with parameters such as responsivity ( R ), photogain (η), and detectivity ( D* ). The formula used to calculate the responsivity ( R ) of the device is as follows Here, I ph is photocurrent and P is the laser power density which is incident on the device and Α is the active area of GSH-Au NCs device. The maximum photoresponsivity obtained from GSH-Au NCs photodetector is 7 A W −1 ( P = 12 W m –2 ) at V ds = 5 V. The value of η of the device was estimated using the formula given as Here, R is the responsivity as calculated in eq , h is Planck’s constant, c is the speed of light, e is the electronic charge, and λ is the incident laser wavelength.…”

Exposing the trion's fine structure by controlling the carrier concentration in hBN-encapsulated MoS2

“…14,15 As the transmission probability of the hBN barrier decreases exponentially with the number of atomic layers, most devices rely on the barriers whose thicknesses fall in the single-nanometers range. 36,[38][39][40][41] However, the electron wave function can penetrate even larger number of layers, up to 9 nm thick. 35,[42][43][44] A parallel pattern can be found in our results, where the charge carrier tunneling seems to occur for structures with bottom hBN thickness below ∼10 nm, as manifested by the strong trion-related emission (see Fig.…”