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We report the comparison of the atomic layer deposited polycrystalline (p-)/amorphous (a-) HfO2 bilayer gate dielectric with p-HfO2/a-Al2O3 for enhanced $\beta $ -Ga2O3 metal oxide semiconductor capacitors (MOSCAPs). A discrepancy in the temperature-dependent hysteretic behaviors is observed, and thus, pulse capacitance–voltage ( ${C}$ – ${V}$ ) measurements are employed to investigate interface properties at the border between the amorphous (Al2O3 or HfO2) and polycrystalline (HfO2) oxide layers. The proposed p-HfO2 /a-HfO2 exhibits similar interface trap densities ( ${D}_{\text {it}}$ ) at the interface between the bilayer dielectric and $\beta \text {-Ga}_{{2}}\text {O}_{{3}}$ , and shows lower border trap density ( ${N}_{\text {bt}}$ ). An effective barrier height of 1.62 eV for the p-HfO2 /a-HfO2 with a breakdown field of 9.1 MV/cm, which is higher than 1.01 eV of p-HfO2 /a-Al2O3, is obtained from the current density-voltage ( ${J}$ – ${V}$ ) characteristics using the Folwer–Nordheim model. Moreover, as compared with a p-HfO2 single layer, the additional a-HfO2 layer on top of p-HfO2 is beneficial to improve hysteretic and leakage characteristics, while maintaining its high-quality interface. The p-HfO2/a-HfO2 bilayer with improved interface properties as well as a large positive flat-band voltage of 4.7 V is a promising candidate for the metal/high- ${k}$ stack of $\beta $ -Ga2O3 MOSCAPs.

Germanium (Ge) has gained great attention not only for future nanoelectronics but for back-end of line (BEOL) compatible monolithic three-dimensional (M3D) integration recently. For high performance and low power devices, various high-k oxide/Ge gate stacks including ferroelectric oxides have been investigated. Here, we demonstrate atomic layer deposited (ALD) polycrystalline (p-) HfO2/GeOX/Ge stack with an amorphous (a-) HfO2 capping layer. The consecutively deposited a-HfO2 capping layer improves hysteretic behaviors ( ${\Delta } {V}$ ) and interface state density ( $\text{D}_{\mathrm{ it}}$ ) of the p-HfO2/GeOX/Ge stack. Furthermore, leakage current density ( ${J}$ ) is significantly reduced $(\times 100)$ by passivating leakage paths through grain boundaries of p-HfO2. The proposed HfO2 layer with the graded crystallinity suggests possible high-k/Ge stacks for further optimized Ge MOS structures.

Highly sensitive and system integrable gas sensors play a significant role in industry and daily life, and MoS2 has emerged as one of the most promising two-dimensional nanomaterials for gas sensor technology. In this study, we demonstrate a scalable and monolithically integrated active-matrix gas sensor array based on large-area bilayer MoS2 films synthesized via two-successive steps: radio-frequency magnetron sputtering and thermal sulfurization. The fabricated thin-film transistors exhibit consistent electrical performance over a few centimeters area and resulting gas sensors detect NO2 with ultra-high sensitivity across a wide detection range, from 1 to 256 ppm. This is due to the abundant grain boundaries of the sputtered MoS2 channel, which perform as active sites for absorption of NO2 gas molecules. The demonstrated active-matrix gas sensor arrays display good switching capabilities and are anticipated to be readily integrated with additional circuitry for different gas sensing and monitoring applications. Sensitive and scalable gas sensors are essential in daily life air-quality monitoring. Here, a monolithically integrated gas sensing circuit based on two-step-grown polycrystalline MoS2 films is fabricated, showing good switching and NO2 gas sensing response in a wide detection range of 1 to 256 ppm.

A Sentaurus TCAD 2-D model of β-Ga2O3 metal-oxide semiconductor field-effect transistors (MOSFETs) with a polycrystalline HfO2 gate-oxide deposited using atomic layer deposition (ALD), which has a semiconductor-on-insulator (SOI) structure, is developed. The results of model shows good agreement with the DC and the AC characteristics of the fabricated device by incorporating proper parameters for the materials, as well as the device models. We also investigate and compare electrical performance of the devices with modified HfO2 gate-oxide geometries. With a reduced HfO2 coverage over the channel, the transconductance (gm) is enhanced, the threshold voltage (Vth) shifts toward a positive voltage, both of which are advantageous for device applications. Moreover, radiation effects during transient operation of the β-Ga2O3 MOSFETs are evaluated and compared for the fabricated and the modified oxide geometries by incorporating carrier generation models with heavy-ions and alpha particles.

Here, we report on heteroepitaxial α-Ga2O3 MOSFETs with a breakdown voltage (BV) of 2.3 kV at a specific on-resistance of 335 mΩ cm2. High-quality α-Ga2O3 layers were grown on a sapphire substrate via halide vapor-phase epitaxy (HVPE). A stack of Ti/Al/Ni/Au was used for the S/D electrode, exhibiting significantly reduced contact resistance as compared with a conventional Ti/Au stack. Consequently, the record BV and mobility of 20.4 cm2 V−1 s−1 were achieved. Moreover, a consistent critical field of 1 MV cm−1 was obtained for variable LGD. Our results are superior to recently reported heteroepitaxial α-/β-Ga2O3 MOSFETs, which is promising toward HVPE α-Ga2O3 based power devices.

In this work, we demonstrate the lateral metal–oxidesemiconductor field-effect transistors (MOSFETs) with β-Ga2O3 film (thickness = 150 nm) grown on a c-plane sapphire substrate by a hydride vapor phase epitaxy (HVPE) method using a CF4-based plasma treatment. By incorporating fluorine (F) the electrical characteristics of the surface and bulk regions of the resistive β-Ga2O3 film could be significantly improved. The analyses by secondary ion mass spectrometry and x-ray photoemission spectroscopy confirmed the formation of the substitutional fluorine, FO, with its peak concentration of 2.3 × 1018 cm−3 at 5 ~ 10 nm deep from the surface and about 1015 ~ 1016 cm−3 in the bulk region. While the argon-plasma treatment was insufficient for making a Ti/Au/Ti metal contact ohmic, the same contact formed on the CF4-treated surface showed an ohmic behavior with specific resistivity of 2.0 × 10−3 Ω·cm2 and contact resistance of 0.8 Ω·m without any post thermal annealing. With the improvement of the electrical properties in both the surface and bulk regions, the HVEP-grown hetero-epitaxial β-Ga2O3 MOSFET exhibited the field-effect mobility of up to 5.3 cm2/V⋅s and on/off ratio of 106.

P-type semiconductors are indispensable for achieving complementary metal oxide semiconductor and integrated circuits based on two-dimensional (2D) semiconductors, and tungsten diselenide (WSe2) and molybdenum ditelluride (MoTe2) are the promising channel materials for PMOS. In this work, we report on the charge trapping effects on hysteretic behavior and field-effect mobility (μ FE) of the p-type WSe2 and MoTe2 FETs using fast pulsed current–voltage (I–V) measurements. The hysteresis is reduced by nearly 98% via ramped pulsed measurements, and μ FE is significantly enhanced via single pulse measurements by minimizing the charge trapping. Moreover, WSe2 FETs are found to be more susceptible to the charge trapping effects compared with MoTe2 FETs; WSe2 FETs exhibit more pronounced enhancement of μ FE and reduction of hysteresis. The intrinsic electrical characteristics of p-type 2D FETs under minimized charge trapping conditions can be investigated using the pulsed I–V characterizations.

Polycrystalline HfO2 dielectrics grown on (−2 0 1) beta-gallium oxide (β-Ga2O3) using high temperature ALD process is investigated. A low capacitance–voltage (C-V) hysteresis of