The transconductance degradation caused by the non-linear resistance of access regions in III-nitride high electron-mobility transistors (HEMTs) is mainly responsible for limiting the RF linearity of the transistor. In this paper, we use Landauer’s transmission theory to develop an analytic electrothermal current-voltage (I-V) model of access regions in III-nitride HEMTs. With only 12 parameters, most of which have a physical origin and can be obtained through experimental calibration, the model is able to correctly predict the I-V behavior in access regions from the drift-diffusive to the quasi-ballistic transport regimes. Model accuracy is demonstrated by comparing the results against experimental and numerical hydrodynamic simulations of ungated transmission line structures with length scales ranging from few 10’s of nanometers to 10’s of micrometers.

In this study, AlGaN/GaN high electron mobility transistors (HEMTs) with a two-dimensional hole gas (2DHG) were investigated. In addition to a two-dimensional electron gas (2DEG) formed at the interface of the AlGaN and GaN layers for being a channel, a 2DHG was designed and formed underneath the channel to be the back gate. The simulated results showed the operation of device can be depletion-mode and enhancement-mode by adjusting the back gate bias. The fabricated devices showed the feasibility of 2DHG back gate control.

In this study, AlGaN/GaN MIS-HEMTs with a p-GaN cap layer and ALD deposited Al2O3 gate insulator were fabricated. Devices with two different thicknesses of p-GaN cap layers were investigated and compared. AlGaN/GaN MIS-HEMT with an 8-nm p-GaN cap showed a better DC characteristics than device with a 5-nm p-GaN cap. The drain current of 662.9 mA/mm, a high on/off current ratio of 2.67×109 and a breakdown voltage of 672 V were measured in device with an 8-nm p-GaN cap. In addition, lateral leakage current was investigated by using adjacent MIS gate structures with a separation of 3 μm to investigate the leakage current.

Preliminary thin films of barium zirconate-titanate (BZT) are grown by pulsed laser deposition from bulk ceramic targets on magnesium oxide (001) substrates. Growth conditions are optimized for film crystallinity and thick (100 nm) films are deposited. These films are seen to be growing with a cube-on-cube epitaxial relation. The lattice constant of the alloy follows Vegard’s law as expected but shows a reasonable amount of non-linearity in the relation between band gap and composition.

With the rising interest in oceanic monitoring, climate awareness and surveillance, the scientific community need for developing autonomous, self-sustaining Unmanned Underwater Vehicles (UUVs) increased as well. Limitations on the size, maneuverability, power consumption, and available on-site maintenance of these UUVs make a number of proposed technologies to power them harder to implement than others; solar energy harvesting stands as one of the more promising candidates to address the need for a long-term energy supply for UUVs due to its relatively small size and ease of deployment. Studies show research groups focusing on the use of Si cells (amorphous and crystalline), InGaP, and more recently Organic Photovoltaics to convert the attenuated solar spectrum under shallow depths (no deeper than 9.1 m) into electrical energy used or stored by the UUV’s power management system (P. P. Jenkins et al. 2014; Walters et al. 2015). In our study, we consider the ternary compound In1-xTlxP that allows for varying the quantum efficiency of the cell, and by extension the overall harvesting efficiency of the system by altering the Tl content (x) in the compound. In1-xTlxP on InP is a low strain system since the compound exhibits very little change in its lattice constant with changing Tl content due to the comparable atomic size and forces of In and Tl allowing for relatively easy growth on InP substrates. The study focuses on studying the spectral response and comparing the performance of an optimized single junction In1-xTlxP cells to In1-yGayP cells while accounting for the optical losses of the solar irradiance underwater for various depths.

Anomalous Hall effect was observed at room temperature in MOCVD-grown GaGdN from a (TMHD)3Gd source, which can contain oxygen in its organic ligand. GaN, and GaGdN grown using a Cp3Gd precursor which does not contain oxygen only showed the ordinary Hall effect. This indicates that oxygen could have a role in magnetic properties of GaGdN. The relationship between the anomalous Hall conductivity and longitudinal conductivity indicated that metallic conduction, hopping of carriers, and scattering-independent mechanisms are likely responsible for the ferromagnetism. However, this still requires further clarification.

Recently, Plasma Assisted Atomic Layer Deposition Technique will easily control the thickness and the composition of semiconductor films. The radical generated by using the plasma techniques, gave the decrease of the defect into the semiconductor films. In this investigation, the relationship between microwave plasma power, nitrogen gas flow rate and concentration of generated nitrogen radical, was evaluated. At the first, Plasma emission spectrum at microwave plasma power (0 to 400W) was measured using a mixed 200sccm argon gas and 10sccm nitrogen gas. Next, the plasma emission spectrum was measured in the mixing of nitrogen gas flow rate (0 to 40sccm) with 200sccm argon gas flow rate. At that time, the microwave plasma power was set to 200W. Nitrogen radical spectrum were identified from all the emission spectrum, and the nitrogen radical intensity was calculated. As a result, the nitrogen radical intensity became the largest at 200sccm argon gas flow rate and 10sccm nitrogen gas flow rate. In addition, the nitrogen radical intensity increased in proportion to the microwave plasma power. The concentration of generated nitrogen radical could be controlled by changing the microwave plasma power and the nitrogen gas flow rate. Mentioned above, nitride thin films will be obtained on Si Substrates by microwave generated remote plasma assisted atomic layer deposition technique.

Issues on tin (Sn) doping in the mist chemical vapor deposition of α-Ga2O3 was attributed to conversion of ionization states of Sn from Sn4+ to Sn2+ and/or out-diffusion of Sn after thermal annealing, resulting in highly resistive films. Silicon (Si) doping, instead, was succeeded by the use of a novel doping source of chloro-(3-cyanopropyl)-dimethylsilane [ClSi(CH3)2((CH2)2CN)]. Si was uniformly incorporated in the α-Ga2O3 films and the electrical properties were stable even after the thermal annealing. The activation ratio as donors was nearly 100%. The carrier (electron) concentration was controlled to the level of 1018 cm-3 by the [Si]/[Ga] ratio in the source solution. The maximum mobility was 31.5 cm2/V⋅s, in contrast to 24 cm2/V⋅s with Sn doping, suggesting advantage of Si doping . However, the reduction in dislocation defects in the α-Ga2O3 films formed owing to heteroepitaxy on sapphire was suggested to be the important subject to be considered in the next stage.

Characterization of three vendor’s bulk semi-insulating GaN:Fe wafers, grown by either hydride vapor phase epitaxy or the ammonothermal method, was performed using: scanning electron microscopy, secondary ion mass spectroscopy, high resolution X-ray diffraction, cathodoluminescence, photoluminescence, and high voltage testing. Although the Fe doping level is significantly different for each growth method, both are promising for the fabrication of PCSS devices operating in the lock-on mode.