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Transition metal dichalcogenides (TMDs) are promising for next-generation electronic and optoelectronic device applications. However, the development of a viable TMD device technology requires an effective strategy for making low-resistance contacts to these materials. In addition, large-area synthesis of low-defect TMD crystals is essential for transforming basic device studies into commercial products...
GaN-based HEMTs have demonstrated outstanding performance in solid-state power amplifiers [1]. Products of fT/fmax and three-terminal breakdown voltage are commonly cited to characterize the high frequency performance of power devices [2]. However, such metrics mix the results of small-signal measurements and DC breakdown measurements taken separately and therefore don't consider side effects of high...
In recent years, GaN trench MOSFETs have been actively investigated to achieve low on-resistance and high breakdown voltage [1-8]. The absence of a JFET region makes the trench MOSFET a favorable device structure to reduce the on-resistance. However, poor (electron) channel mobility in GaN trench MOSFETs lead to increased channel resistance. This could potentially result in reliability issues and/or...
Strained heteroepitaxial HEMTs without the mechanical support of a substrate have been demonstrated only for small-sized AlGaN/GaN membranes, i.e., the substrate was removed from within the immediate vicinity of the transistor area [1]. Such transistors have exhibited improved breakdown voltage and frequency response. However, wafer-scale substrate removal has been considered detrimental to the heterostructure...
We present small-signal measurements on graded AlGaN channel polarization-doped field-effect transistors (PolFETs) that show constant current gain cutoff frequency, fT, and power gain cutoff frequency, fmax, profiles as a function of current density or gate bias. AlGaN/GaN high electron mobility transistors (HEMTs) are suitable candidates for mm-wave and THz amplifiers. However their transconductance,...
One of the main challenges inhibiting the integration of 2D crystals into top-gate field-effect transistors (FETs) is deposition of a uniform, scalable, high-quality dielectric. The most common and controlled method of deposition of thin dielectric films is atomic layer deposition (ALD); however, the inert surface of 2D materials offers no nucleation sites for the ALD precursors, resulting in non-uniform...
Molybdenum disulfide (MoS2), a member of the transition metal dichalcogenide (TMD) family, is a 2D semiconductor with a direct bandgap of ∼1.8 eV for single layers. Its bandgap allows for high Ion/Ioff metal-oxide semiconducting field-effect transistors (FETs). More relevant for radio frequency (RF) wireless applications, theoretical studies predict MoS2 to have saturation velocities, Vsat > 3×10...
Black phosphorus (BP) has recently attracted wide interest for various applications and is particularly appealing for low power tunneling devices due to several unique properties such as a small bandgap and small carrier effective masses. Here, we report the first experimental demonstration of band-to-band tunneling (BTBT) in BP. In addition, we also report fully top gated BP FETs with record-high...
Gallium oxide (Ga2O3) is attractive for power devices owing to its wide bandgap of 4.5 eV and the availability of economical device-quality native substrates. Research on Ga2O3 Schottky barrier diodes and field-effect transistors (FETs) has seen rapid recent progress [1]. An unexplored area of immense interest is the radiation tolerance of these devices, whose high-voltage and high-temperature capabilities...
β-Ga2O3 is a suitable material for next-generation high-power devices because it has excellent material properties and mass productivity. In the past, we have demonstrated field-plated Ga2O3 Schottky barrier diodes (SBDs) with nearly ideal reverse characteristics limited mainly by the thermionic field emission (TFE) leakage current. [1] However, the TFE current, that is, leakage current, was very...
Two-dimensional (2D) semiconductor, such as transition metal dichalcogenides (TMDs) and black phosphorus (BP), have been extensively studied for future transistor applications because of the atomic thin layered structure for excellent immunity to short channel effects. BP has been considered to be promising for future p-type channel material, because of its high hole mobility, up to 5000 cm2/Vs at...
β-Gallium oxide (Ga2O3) is an increasingly attractive choice for next generation power electronics applications due to its large bandgap, good mobility giving rise to a high Baliga's figure of merit (BFoM), mature bulk and thin film growth technologies with excellent doping control over several orders [1-3]. Moreover, recent experimental MOSFETs have shown large breakdown voltages (750 V), large on...
Previous studies have shown that optical and/or injection pumping of graphene can enable negative-dynamic conductivity in the terahertz (THz) spectral range, which may lead to new types of THz lasers and light-emitting devices [1-4]. Recently we obtained preliminary results of single-mode THz lasing in a forward-biased graphene structure with a lateral p-i-n junction in a distributed-feedback dual-gate...
Deep UV (DUV) light-emitting diodes (LEDs) are finding increased application in many areas including water purification and sterilization. Sub-270 nm emission is ideal for these applications since bacterial DNA absorbs strongly in this wavelength regime. To extract high energy photons (∼5 eV), the LED cladding regions must be transparent and therefore consist of high Aluminum content (>60%) n-...
Photoconductive antennas are extensively used in time-domain terahertz imaging and spectroscopy systems to generate terahertz radiation [1, 2]. These emitters consist of a terahertz antenna fabricated on a photoconductive semiconductor. When the semiconductor is pumped by a femtosecond laser and a bias voltage is applied to the antenna arms, an ultrafast photocurrent is generated. As this photocurrent...
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