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Biography
Mahdi Moradinasab was born in Tehran, Iran, in 1982. He studied electrical engineering at the University of Teheran, where he received the MSc degree in 2009. He joined the Institute for Microelectronics in December 2011. His scientific interests include modeling of optoelectronic and photonic devices.
Graphene Superlattice-Based Photodetectors
Nanostructures made from graphene and graphene related materials or from traditional compound semiconductors are promising building blocks for light sources and detectors in a broad frequency range. By cutting graphene into a few nanometer-wide nanoribbons, the bandgap can be tuned to a certain extent by the confinement of the electronic wave function. One dimensional graphene superlattices provide precisely tunable energy gaps for optical applications.
Single-layer hexagonal Boron Nitride (BN) can be patterned into nanoribbons which exhibit large enough band gaps and qualitatively different properties from those of graphene related materials. Embedding
graphene nanostructures in BN lattices increases flexibility of bandgap engineering for optical transitions.
The optical properties of graphene nanoribbon superlattices embedded in BN sheets and the possibility of using such structures as photodetectors are studied. We propose a set of tight-binding parameters for the investigated structures, which yields an excellent agreement with first-principles results. The results indicate that the optical spectrum of a BN-confined graphene SuperLattice (BNSL) contains more absorption peaks and allows more optical intersubband transitions compared with a Hydrogen-passivated SuperLattice (HSL) of the same geometry. Employing the non-equilibrium Green's function method, the photocurrents and quantum efficiencies are evaluated and compared for both devices at various incident photon energies. Using a statistical approach, the role of line-edge roughness on the optical properties of graphene-based superlattices is investigated. The results indicate that the quantum efficiency and photoresponsivity decrease in the presence of line-edge roughness. For HSLs, induced states appear and increase with the roughness amplitude, which results in the appearance of an additional peak in photocurrent spectrum. In comparison with HSLs, BNSLs exhibit more robust optical properties in the presence of line-edge roughness due to the stable edge atom configuration.
Fig. 1: The ideal and average photocurrent spectra for (a) HSL(11) and (b) BNSL(11) at various roughness amplitudes.
