Carrier transport mechanisms in metal-semiconductor-metal (MSM) devices: A review study

This review provides a comprehensive analysis of carrier transport mechanisms in Metal–semiconductor–metal (MSM) devices, with a focus on the distinctive charge transport behavior arising from their dual Metal–semiconductor interface configuration. While existing reviews, such as those on semiconductor nanostructures, have extensively explored carrier dynamics in individual nanowires, nanocrystals, and related nanoscale architectures with ohmic or single Schottky contacts, this work specifically addresses MSM structures characterized by dual Metal–semiconductor interface configuration. A diverse range of MSM structures are discussed, including those based on silicon carbide (SiC), gallium nitride (GaN), aluminum gallium nitride (Al${}_x$Ga${}_{1-x}$N), nitrogen-doped ZnO (ZnO:N), graphene, and tin dioxide (SnO${}_2$), fabricated using different techniques such as RF sputtering, molecular beam epitaxy, and metal–organic chemical vapor deposition (MOCVD). Transport phenomena such as space charge limited conduction (SCLC), thermionic emission, thermionic field emission (TFE), Poole–Frenkel emission (PFE), and variable range hopping (VRH) are examined in relation to their contributions toward the nonlinear current–voltage (I–V) characteristics commonly exhibited in MSM devices. The study places strong emphasis on the extraction and physical interpretation of key parameters: SCLC exponent, trap density, and critical voltage in the SCLC regime; Schottky barrier height (${\Phi }_B$) and ideality factor ($n$) in thermionic emission; energy parameters such as ${\varepsilon }^{\prime }$ and $E_{00}$ in TFE; high-frequency dielectric constant (${\varepsilon }_s$) and trap ionization energy (${\Phi }_t$) in PFE; and the characteristic temperature ($T_0$) in VRH, which relates to the density and spatial distribution of localized states. By connecting these extracted quantities to trap dynamics, interface phenomena, and field effects, the review offers a structured framework for interpreting the nonlinearities observed in experimental I–V responses. This synthesis serves as a technically grounded reference for advancing the modeling, characterization, and design of MSM devices in emerging applications such as photodetection, gas sensing, high-power electronics, and transparent optoelectronics.