Opto-electronics in van der Waals heterostructures

Atomically thin p-n junction: The advent of various 2d-materials like graphene, transition metal di-chalcogenides (TMDs) and, the existence of well-established device fabrication technique presented an opportunity to take the solid-state device technology to the atomically thin limit. It has been an area of active research in contemporary physics for more than two decades now. In this context, atomically thin PN junctions made of 2D-materials have been studied extensively, as PN junctions form one of the vital building blocks for modern day semiconductor device technology. We study the room temperature optoelectronic properties of an atomically thin vertical hetero-PN junction made of TMD semiconductors like MoS2 and MoTe2. We found anomalous gate dependent photo-conductivity response and high photo responsivity of the order of 105 A/W from the junction. While the former has been attributed to enhanced interaction between the interlayer carriers due to the junction’s atomically sharp nature, the latter has been associated with efficient separation of photo-generated carriers due to the built-in electric field of the junction.

Twisted bilayer graphene: Twisted bilayer graphene (tBLG) is a new system that exhibits fundamental properties distinct from those of Bernal stacked bilayer graphene and are of great current interest because of its exotic electronic and optical phenomena. The energy separation between nearly flat bands and the nearest conduction and valence band is of the order of the photons’ energy used in optical studies, thus making tBLG an exciting candidate for optical study. The optical properties are closely related to the changes in the electronic band structure and Van Hove singularities (VHS), which in turn depends strongly on the twist angle. Therefore, the optical properties of tBLG vary significantly from bilayer and multilayer graphene Our work encompasses a wide variety of optical studies, such as the study of low-energy Raman modes, the evolution of electronic band structure, phonon dispersion, etc. This area of research has shown a lot of potential in the last couple of years and promises exciting research opportunities.


  1. Photo-tunable transfer characteristics in MoTe 2–MoS 2 vertical heterostructure; AK Paul et al. npj 2D Materials and Applications 1 (1), 1-7 (2017).
  2. Enhancing photoresponsivity using MoTe2-graphene vertical heterostructures; M Kuiri et al. Applied Physics Letters 108 (6), 063506 (2016).

(Top left): Optical image together with AFM image of the MoTe2/MoS2 vertical heterostructure. (Top-right): Schematic of the experimental setup. (Middle left): I-V characteristic of atomically thin type-II p-n junction. (Middle-right): Photo-response of the junction. (Bottom-left): Light induced transfer characteristic curves. (Bottom-right): High photo-responsivity of the junction.