Investigation of the Interfaces in Schottky Diodes Using Equivalent Circuit Models

The metal–semiconductor contact is one of the most critical factors that determine the performance of semiconductor devices such as Schottky barrier diodes (SBDs). SBDs between conductive carbon thin films and silicon have attracted attention due to their high performance and potential low cost of fabrication. Here, we introduce impedance spectroscopy (IS) as a powerful technique to characterize such SBDs. The electrical and structural characteristics of carbon–silicon SBDs between silicon and two different types of conductive carbon thin films have been investigated. Modeling the data with an extended equivalent circuit model reveals the effects of the metal electrode contacts of SBDs for the first time. From dc current–voltage measurements, diode parameters including the ideality factor, the Schottky barrier height, and the series resistance are extracted. Through use of analysis with IS, additional information on the Schottky contact is obtained, such as the built-in potential and more reliable barrier height values. Thus, IS can be utilized to analyze interfaces between metals and semiconductors in great detail by electrical means

Chemically Modulated Graphene Diodes

We report the manufacture of novel graphene diode sensors (GDS), which are composed of monolayer graphene on silicon substrates, allowing exposure to liquids and gases. Parameter changes in the diode can be correlated with charge transfer from various adsorbates. The GDS allows for investigation and tuning of extrinsic doping of graphene with great reliability. The demonstrated recovery and long-term stability qualifies the GDS as a new platform for gas, environmental, and biocompatible sensors

Highly Sensitive Electromechanical Piezoresistive Pressure Sensors Based on Large-Area Layered PtSe₂ Films

Two-dimensional (2D) layered materials are ideal for micro- and nanoelectromechanical systems (MEMS/NEMS) due to their ultimate thinness. Platinum diselenide (PtSe₂), an exciting and unexplored 2D transition metal dichalcogenide material, is particularly interesting because its low temperature growth process is scalable and compatible with silicon technology. Here, we report the potential of thin PtSe₂ films as electromechanical piezoresistive sensors. All experiments have been conducted with semimetallic PtSe₂ films grown by thermally assisted conversion of platinum at a complementary metal–oxide–semiconductor (CMOS)-compatible temperature of 400 °C. We report high negative gauge factors of up to −85 obtained experimentally from PtSe₂ strain gauges in a bending cantilever beam setup. Integrated NEMS piezoresistive pressure sensors with freestanding PMMA/PtSe₂ membranes confirm the negative gauge factor and exhibit very high sensitivity, outperforming previously reported values by orders of magnitude. We employ density functional theory calculations to understand the origin of the measured negative gauge factor. Our results suggest PtSe₂ as a very promising candidate for future NEMS applications, including integration into CMOS production lines

High-Performance Hybrid Electronic Devices from Layered PtSe₂ Films Grown at Low Temperature

Layered two-dimensional (2D) materials display great potential for a range of applications, particularly in electronics. We report the large-scale synthesis of thin films of platinum diselenide (PtSe₂), a thus far scarcely investigated transition metal dichalcogenide. Importantly, the synthesis by thermally assisted conversion is performed at 400 °C, representing a breakthrough for the direct integration of this material with silicon (Si) technology. Besides the thorough characterization of this 2D material, we demonstrate its promise for applications in high-performance gas sensing with extremely short response and recovery times observed due to the 2D nature of the films. Furthermore, we realized vertically stacked heterostructures of PtSe₂ on Si which act as both photodiodes and photovoltaic cells. Thus, this study establishes PtSe₂ as a potential candidate for next-generation sensors and (opto-)­electronic devices, using fabrication protocols compatible with established Si technologies

Direct Observation of Degenerate Two-Photon Absorption and Its Saturation in WS₂ and MoS₂ Monolayer and Few-Layer Films

The optical nonlinearity of WS₂ and MoS₂ monolayer and few-layer films was investigated using the <i>Z</i>-scan technique with femtosecond pulses from the visible to the near-infrared range. The nonlinear absorption of few- and multilayer WS₂ and MoS₂ films and their dependences on excitation wavelength were studied. WS₂ films with 1–3 layers exhibited a giant two-photon absorption (TPA) coefficient as high as (1.0 ± 0.8) × 10⁴ cm/GW. TPA saturation was observed for the WS₂ film with 1–3 layers and for the MoS₂ film with 25–27 layers. The giant nonlinearity of WS₂ and MoS₂ films is attributed to a two-dimensional confinement, a giant exciton effect, and the band edge resonance of TPA