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Direct epitaxial integration of magnetic layers with wide bandgap nitride semiconductors will enable spin-controlled transport and photonic phenomena, seeding ideas for functional spintronic devices. Using plasma-assisted molecular beam epitaxy (MBE) in a previously unexplored window, significantly improved ferrimagnetic Mn4N layers are successfully grown on GaN with ~ 1 nm surface roughness. Distinct from earlier reports, the Mn4N layers grown on GaN are found to be 001 oriented with 12-fold in-plane symmetry in the diffraction pattern. This unique epitaxial registry originates from three equivalent rotational domains. The ferrimagnetic magnetotransport properties of low growth temperature Mn4N layers on GaN are comparable to those reported on cubic substrates such as MgO. However, a sign-flip of the Hall resistance is discovered for Mn4N layers grown above 300 °C.

Power and RF electronics applications have spurred massive investment into a range of wide and ultrawide bandgap semiconductor devices which can switch large currents and voltages rapidly with low losses. However, the end systems using these devices are often limited by the parasitics of integrating and driving these chips from the silicon complementary metal–oxide-semiconductor-based design (CMOS) circuitry necessary for complex control logic. For that reason, implementation of CMOS logic directly in the wide bandgap platform has become a way for each maturing material to compete. This review examines potential CMOS monolithic and hybrid approaches in a variety of wide bandgap materials.

In this paper, we map the ferroelectric properties of 22% and 30% scandium-doped aluminum nitride (ScAlN) thin films with the goal to engineer low coercive fields for low-voltage post-CMOS compatible RF frontends. ScAlN films, 200 nm and 300 nm thick, were deposited on platinum and molybdenum electrodes. Lateral and vertical capacitors were tested across various electric field strengths, frequencies, and electrode sizes. Measured coercive field and remnant polarization values were between 3.9-6.2 MV/cm and $58-170\ \mu \mathrm{C}/\text{cm}^{2}$ . Frequency and device area-dependence were studied to identify trends towards low coercive fields. A comparison of lateral and vertical capacitors on the same ScAlN films shows the impact of charge-traps due to current-crowding in lateral devices. Finally, an anomalous observation relating doping concentration and film stress with coercive field and remnant polarization is reported to present the potential for decoupled tuning knobs for ferroelectric engineering properties ScAlN.

This paper reports the temperature-dependent ferroelectric properties of sputtered ferroelectric Al 0.70 Sc 0.30 N. The coercive field is experimentally demonstrated to decrease by 1.5 MV/cm in 300 nm films in the temperature range of 20– 193 0C, corresponding to an average linear coefficient of decrease of 8.8 kV/0C. In the same range, the remnant polarization varies by 23.5% between 90-114 µC/cm2 without a significant drop-off at higher temperatures. Thermally cycling the chip between room temperature and the highest achievable temperature of 193 0C shows a reversible tuning of the coercive field, paving the path towards on-chip ovenization-based control of ferroelectric properties. The dielectric breakdown under AC and DC testing are driven by filamentary and thermally driven breakdown processes respectively. These breakdown processes suggest the potential for high frequency operation of sputtered Al 0.70 Sc 0.30 N as a ferroelectric thin film at elevated temperatures with low leakage.

A strong need exists for a wide-bandgap p-type transistor counterpart of the n-channel GaN HEMTs for power electronics and novel RF circuits. In this work, the first p-channel nitride transistors that break the GHz speed barrier are demonstrated. By leveraging the unique single-channel high-density polarization-induced 2D hole gas of the GaN/AlN heterostructure, best-in-class contact resistances, and scaled T-gate design, p-channel transistor on-currents of 428 mA/mm are observed, with cutoff frequencies in the 20 GHz regime. These observations demonstrate the unique enabling role of the polarization discontinuity at the GaN/AlN semiconductor heterojunction and offer significant hope for a new high-speed and high-voltage wide-bandgap CMOS device platform for applications in RF and power electronics domains.

Epitaxial multilayer heterostructures of ScxAl1−xN/GaN with Sc contents x = 0.11–0.45 are found to exhibit significant differences in structural quality, chemical impurity levels, and electronic properties depending on the starting Sc source impurity levels. A higher purity source leads to a 2–3 orders of magnitude reduction in the carbon, oxygen, and fluorine unintentional doping densities in MBE-grown ScxAl1−xN/GaN multilayers. Electrical measurements of ScxAl1−xN/n+GaN single heterostructure barriers show a 5–7 orders of magnitude reduction in the electrical leakage for films grown with a higher purity Sc source at most Sc contents. The measured chemical and electrical properties of epitaxial ScxAl1−xN highlight the importance of the starting Sc source material purity for epitaxial device applications that need these highly piezoelectric and/or ferroelectric transition-metal nitride alloys.

We report the synthesis of large-scale continuous MoSe2 films on SiO2/Si substrates by atmospheric pressure chemical vapor deposition (CVD). As-grown thin films were composed of a continuous monolayer of MoSe2 and extended up to a millimeter scale. The CVD-grown monolayer MoSe2 films were uniform in thickness and highly crystalline with hexagonal crystal structures. Raman and photoluminescence spectra showed that CVD-grown monolayer MoSe2 films have similar vibrational and optical properties to those of mechanically exfoliated monolayer MoSe2. These results demonstrate that the CVD-grown monolayer MoSe2 films have reasonably high quality comparable to that of mechanically exfoliated monolayer MoSe2 flakes.

Mn4N is a compound magnetic material that can be grown using MBE while exhibiting several desirable magnetic properties such as strong perpendicular magnetic anisotropy, low saturation magnetization, large domain size, and record high domain wall velocities. In addition to its potential for spintronic applications exploiting spin orbit torque with epitaxial topological insulator/ferromagnet bilayers, the possibility of integrating Mn4N seamlessly with the wide bandgap semiconductors GaN and SiC provides a pathway to merge logic, memory and communication components. We report a comparative study of MBE grown Mn4N thin films on four crystalline substrates: cubic MgO, and hexagonal GaN, SiC and sapphire. Under similar growth conditions, the Mn4N film is found to grow single crystalline on MgO and SiC, polycrystalline on GaN, and amorphous on sapphire. The magnetic properties vary on the substrates and correlate to the structural properties. Interestingly, the field dependent anomalous Hall resistance of Mn4N on GaN shows different behavior from other substrates such as a flipped sign of the anomalous Hall resistance.

Nitride-based semiconductors have received considerable attention during the last decade due to their outstanding properties for optoelectronic, high frequency, and high power applications. The integration of GaN and Si (100) devices on the same chip would enable a vast array of new applications, from novel power distribution schemes in Si microsystems, to power digital-toanalog converters and new opportunities for optoelectronic devices integrated on a Si platform. This paper aims to summarize some of the recent results on the heterogeneous integration of GaN and Si (100) devices and circuits by using a hybrid 4" wafer bonding technology.

Back-gated MoSe2 thin-film transistors (TFTs) with an Al2O3-capping layer were fabricated, and the device characteristics of the MoSe2 TFTs that are dependent on the Al2O3-capping-layer passivation were investigated. The output drain current was doubled, the fluctuation of the output current was suppressed, and the threshold voltage of the MoSe2 TFTs was negatively shifted with the Al2O3-capping layer. The on/off-current ratio of the MoSe2 TFTs is approximately six decades regardless of the Al2O3-capping layer, but the field-effect mobility was greatly increased from 2.86 cm2/Vs to 10.26 cm2/Vs after the deposition of the Al2O3-capping layer. According to the results of this study, the Al2O3-capping layer can enhance the device characteristics of MoSe2 TFTs.

We investigated the dependence of electron mobility on the thickness of MoS2 nanosheets by fabricating bottom-gate single and few-layer MoS2 thin-film transistors with SiO2 gate dielectrics and Au electrodes. All the fabricated MoS2 transistors showed on/off-current ratio of similar to 10(7) and saturated output characteristics without high-k capping layers. As the MoS2 thickness increased from 1 to 6 layers, the field-effect mobility of the fabricated MoS2 transistors increased from similar to 10 to similar to 18 cm(2)V(-1)s(-1). The increased subthreshold swing of the fabricated transistors with MoS2 thickness suggests that the increase of MoS2 mobility with thickness may be related to the dependence of the contact resistance and the dielectric constant of MoS2 layer on its thickness. (C) 2016 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).