Geometric Diode Modeling for Energy Harvesting Applications

Transition metal dicalchogenides (TMDCs) are material whose fundamental structure consists of one atom of transition metal and two atoms of chalcogen. The interest on these compounds has constantly increased because of their peculiar chemical and physical properties. Among TMDCs, we can find molybdenum ditelluride, tungsten diselenide, molybdenum diselenide, and molybdenum disulfide (MoTe
2
, WeSe
2
, MoSe
2
, and MoS
2
, respectively). When using few-atom-thick layers, MoS
2
(also known as “molybdenite” has shown the possibility of outperforming the current silicon technology and of being used in many different applications, such as sensors, solar cells, photo detectors, field-effect transistor, and geometric diodes. The latter present different advantages with respect to classical diode structures because a geometric diode is created by etching channels in a planar semiconductor/semimetal, thus forming a so-called “self-switching diode” (SSD), which has demonstrated to detect both microwave and THz signals. An SSD is different from classical diodes, in the sense that no junctions are necessary (hence no doping), and its physics relies upon a nonlinear current, which flows through nanometer-sized parallel channels and is controlled by field-effect phenomena. The simplicity in the fabrication process, a higher breakdown voltage, and less parasitic effects are among the advantages of such diodes. In this work, by means of full-wave drift-diffusion equation-based simulations, we show a physical model for MoS
2
-based geometric diodes, which have lately demonstrated to be possible candidates in both microwave and solar energy harvesting applications. The validation of this model will be performed through comparisons with experimental data retrieved from two different geometrical/technological configurations. In the first one, we consider a bulk (i.e., multilayer, bandgap of 1.2 eV) MoS
2
and a hydrogen silsesquioxane (HSi$\mathrm{O}_{3/2})_{n}$ encapsulation; the second one is an analogous structure that comprises a monolayer MoS
2
(bandgap of 1.85 eV) with an A$1_{2}\mathrm{O}_{3}$ encapsulation obtained by depositing a 3-nm-thick layer of Al to prevent the oxidation of the MoS
2
monolayer.