We are pleased to introduce the collection, 2022 Retrospective: Semiconducting Materials and Devices. This collection aims to showcase original research and review-based papers on the most exciting developments of the past couple of years. The work presented here highlights the broad diversity of research performed across the section, and aims to put a spotlight on the main areas of interest. All research presented here seeks to display strong advances in theory, experiment, and methodology with applications to compelling problems. Authors are encouraged to showcase their most recent discoveries and to kickstart scientific discourse around them.

Purdue University

The University of Manchester

Frontiers in Materials

Semiconducting Materials and Devices

Frontiers in Electronic Materials

2022 Retrospective: Semiconducting Materials and Devices

van der Waals antiferromagnets with chemical formula MPX3 (M = V, Mn, Fe, Co, Ni, Cd; X = S, Se) are superb platforms for exploring the fundamental properties of complex chalcogenides, revealing their structure-property relations and unraveling the physics of confinement. Pressure is extremely effective as an external stimulus, able to tune properties and drive new states of matter. In this review, we summarize experimental and theoretical progress to date with special emphasis on the structural, magnetic, and optical properties of the MPX3 family of materials. Under compression, these compounds host inter-layer sliding and insulator-to-metal transitions accompanied by dramatic volume reduction and spin state collapse, piezochromism, possible polar metal and orbital Mott phases, as well as superconductivity. Some responses are already providing the basis for spintronic, magneto-optic, and thermoelectric devices. We propose that strain may drive similar functionality in these materials.

van der Waals antiferromagnets with chemical formula MPX3 (M = V, Mn, Fe, Co, Ni, Cd; X = S, Se) are superb platforms for exploring the fundamental properties of complex chalcogenides, revealing their structure-property relations and unraveling the physics of confinement. Pressure is extremely effective as an external stimulus, able to tune properties and drive new states of matter. In this review, we summarize experimental and theoretical progress to date with special emphasis on the structural, magnetic, and optical properties of the MPX3 family of materials. Under compression, these compounds host inter-layer sliding and insulator-to-metal transitions accompanied by dramatic volume reduction and spin state collapse, piezochromism, possible polar metal and orbital Mott phases, as well as superconductivity. Some responses are already providing the basis for spintronic, magneto-optic, and thermoelectric devices. We propose that strain may drive similar functionality in these materials.

MPX3 van der Waals magnets under pressure (M = Mn, Ni, V, Fe, Co, Cd; X = S, Se)

To realize low-cost, environmentally friendly electronic devices and circuits, there is currently a strong trend to explore plant-based dielectric materials because they can be responsibly sourced from agricultural or forest vegetation, are generally water-soluble, and possess good electrical insulator properties. In this contribution, organic field-effect transistors (OFETs) using a biopolymer dielectric obtained from exudates of Anacardium occidentale Linn. trees, namely, cashew gum (CG), are reported. To characterise the physical and dielectric properties of the gum, thin films and metal-insulator-metal (MIM) capacitors were prepared and characterized. To evaluate the material’s performance in OFETs, bottom-gate top-contact (BGTC) p-channel poly [3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo (3,4-c)pyrrole-1,4-dione) thieno (3,2-b) thiophene]:polymethyl methacrylate (DPPTTT:PMMA) transistors were engineered and studied. The fabricated MIM capacitors display a comparatively high areal capacitance of 260 nF/cm2 at 1 kHz for 130 nm thick films. As a result, the solution-processed DPPTTT:PMMA OFETs favourably operate at 3 V with the average saturation field-effect mobility equal to 0.20 cm2/Vs., threshold voltage around −1.4 V, subthreshold swing in the region of 250 mV/dec, and ON/OFF current ratio well above 103. As such, cashew gum emerges as a promising dielectric for sustainable manufacturing of solution-processed organic FETs.

To realize low-cost, environmentally friendly electronic devices and circuits, there is currently a strong trend to explore plant-based dielectric materials because they can be responsibly sourced from agricultural or forest vegetation, are generally water-soluble, and possess good electrical insulator properties. In this contribution, organic field-effect transistors (OFETs) using a biopolymer dielectric obtained from exudates of Anacardium occidentale Linn. trees, namely, cashew gum (CG), are reported. To characterise the physical and dielectric properties of the gum, thin films and metal-insulator-metal (MIM) capacitors were prepared and characterized. To evaluate the material’s performance in OFETs, bottom-gate top-contact (BGTC) p-channel poly [3,6-di(2-thien-5-yl)-2,5-di(2-octyldodecyl)-pyrrolo (3,4-c)pyrrole-1,4-dione) thieno (3,2-b) thiophene]:polymethyl methacrylate (DPPTTT:PMMA) transistors were engineered and studied. The fabricated MIM capacitors display a comparatively high areal capacitance of 260&nbsp;nF/cm2 at 1&nbsp;kHz for 130&nbsp;nm thick films. As a result, the solution-processed DPPTTT:PMMA OFETs favourably operate at 3&nbsp;V with the average saturation field-effect mobility equal to 0.20&nbsp;cm2/Vs., threshold voltage around −1.4&nbsp;V, subthreshold swing in the region of 250&nbsp;mV/dec, and ON/OFF current ratio well above 103. As such, cashew gum emerges as a promising dielectric for sustainable manufacturing of solution-processed organic FETs.

Towards sustainable, solution-processed organic field-effect transistors using cashew gum as the gate dielectric

Organic Electrochemical Transistors (OECTs) are suitable for developing ultra-sensitive bioelectronic sensors. In the organic electrochemical transistors architecture, the source-drain channel is made of a conductive polymer film either cast from a formulated dispersion or electrodeposited from a monomer solution. The commercial poly(3,4-ethylenedioxidethiophene)/poly(styrene sulfonate) (PEDOT:PSS) water dispersion is the workhorse of organic bioelectronics for its high conductance, low impact and ease of processability. In this study, a hybrid organic electrochemical transistors channel fabrication strategy is presented, where electrochemical deposition of a PEDOT/X (with X indicating the counterion) is performed on a dispersion-cast PEDOT:PSS film. Six different counterions where used: X = PSS, Nafion, Hyaluronate, Dextran sulfate, Dexamethasone phosphate and tauroursodeoxycholic acid, each potentially endowing organic electrochemical transistors with additional functions such as ion exchange and pharmacological activity upon release of X. The PEDOT/X-PEDOT:PSS bilayers were characterized by means of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and focused ion beam tomography combined with scanning electron microscopy (FIB-SEM). In addition, their respective organic electrochemical transistorss were characterized and compared to PEDOT:PSS organic electrochemical transistors. Our results show that the hybrid bilayer strategy is viable to fabricate multifunctional organic electrochemical transistorss with biologically-relevant function, thereby retaining the outstanding figures of merit of commercial PEDOT:PSS.

Organic Electrochemical Transistors (OECTs) are suitable for developing ultra-sensitive bioelectronic sensors. In the organic electrochemical transistors architecture, the source-drain channel is made of a conductive polymer film either cast from a formulated dispersion or electrodeposited from a monomer solution. The commercial poly(3,4-ethylenedioxidethiophene)/poly(styrene sulfonate) (PEDOT:PSS) water dispersion is the workhorse of organic bioelectronics for its high conductance, low impact and ease of processability. In this study, a hybrid organic electrochemical transistors channel fabrication strategy is presented, where electrochemical deposition of a PEDOT/X (with X indicating the counterion) is performed on a dispersion-cast PEDOT:PSS film. Six different counterions where used: X = PSS, Nafion, Hyaluronate, Dextran sulfate, Dexamethasone phosphate and tauroursodeoxycholic acid, each potentially endowing organic electrochemical transistors with additional functions such as ion exchange and pharmacological activity upon release of X. The PEDOT/X-PEDOT:PSS bilayers were characterized by means of electrochemical impedance spectroscopy (EIS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and focused ion beam tomography combined with scanning electron microscopy (FIB-SEM). In addition, their respective organic electrochemical transistorss were characterized and compared to PEDOT:PSS organic electrochemical transistors. Our results show that the hybrid bilayer strategy is viable to fabricate multifunctional organic electrochemical transistorss with biologically-relevant function, thereby retaining the outstanding figures of merit of commercial PEDOT:PSS.

Multifunctionally-doped PEDOT for organic electrochemical transistors

Oxide semiconductors have attracted revived interest for complementary metal–oxide–semiconductor (CMOS) back-end-of-line (BEOL) compatible devices for monolithic 3-dimensional (3D) integration. To obtain a high-quality oxide/semiconductor interface and bulk semiconductor, it is critical to enhance the performance of oxide semiconductor transistors. Atomic layer-deposited (ALD) indium oxide (In2O3) has been reported with superior performance such as high drive current, high mobility, steep subthreshold slope, and ultrathin channel. In this work, the interface and bulk traps in the MOS gate stack of ALD In2O3 transistors are systematically studied by using the C–V and conductance method. A low EOT of 0.93 nm is achieved directly from the accumulation capacitance in C–V measurement, indicating a high-quality gate oxide and oxide/semiconductor interface. Defects in bulk In2O3 with energy levels in the subgap are confirmed to be responsible for the conductance peak in GP/ω versus ω curves by TCAD simulation of C–V and G–V characteristics. A high n-type doping of 1×1020/cm3 is extracted from C–V measurement. A high subgap density of states (DOS) of 3.3×1020 cm−3 eV−1 is achieved using the conductance method, which contributes to the high n-type doping and high electron density. The high n-type doping further confirms the capability of channel thickness scaling because the charge neutrality level aligns deeply inside the conduction band.

Oxide semiconductors have attracted revived interest for complementary metal–oxide–semiconductor (CMOS) back-end-of-line (BEOL) compatible devices for monolithic 3-dimensional (3D) integration. To obtain a high-quality oxide/semiconductor interface and bulk semiconductor, it is critical to enhance the performance of oxide semiconductor transistors. Atomic layer-deposited (ALD) indium oxide (In2O3) has been reported with superior performance such as high drive current, high mobility, steep subthreshold slope, and ultrathin channel. In this work, the interface and bulk traps in the MOS gate stack of ALD In2O3 transistors are systematically studied by using the C–V and conductance method. A low EOT of 0.93&nbsp;nm is achieved directly from the accumulation capacitance in C–V measurement, indicating a high-quality gate oxide and oxide/semiconductor interface. Defects in bulk In2O3 with energy levels in the subgap are confirmed to be responsible for the conductance peak in GP/ω versus ω curves by TCAD simulation of C–V and G–V characteristics. A high n-type doping of 1×1020/cm3 is extracted from C–V measurement. A high subgap density of states (DOS) of 3.3×1020&nbsp;cm−3&nbsp;eV−1 is achieved using the conductance method, which contributes to the high n-type doping and high electron density. The high n-type doping further confirms the capability of channel thickness scaling because the charge neutrality level aligns deeply inside the conduction band.

Characterization of Interface and Bulk Traps in Ultrathin Atomic Layer-Deposited Oxide Semiconductor MOS Capacitors With HfO2/In2O3 Gate Stack by C-V and Conductance Method

In recent years, the infrared electrochromic devices based on acid doped polyaniline films have achieved much progress, which has not been summarized before. This is important to accelerate the development of this field. In this paper, we will briefly review some representing work about the infrared electrochromic properties of acid doped polyaniline films, which were reported in the last 5 years.

In recent years, the infrared electrochromic devices based on acid doped polyaniline films have achieved much progress, which has not been summarized before. This is important to accelerate the development of this field. In this paper, we will briefly review some representing work about the infrared electrochromic properties of acid doped polyaniline films, which were reported in the last 5&#xa0;years.