0.25µm GaN HEMTs performance dependence from epitaxial and geometrical parameters has been investigated by means of numerical simulations.
A single-heterojunction GaN HEMT structure with an iron doped buffer layer also including a mushroom-gate layout forming a gate-connected field-plate over the device SiN passivation layer was considered.
Numerical simulations including static-IV characteristics and breakdown voltage estimation, small signal analysis and double pulse-IV characteristics have been carried out on more than 400 different structures.
Simulations results showed that contact resistance, gate-source spacing, barrier thickness and AlGaN/SiN interface trap density are critical for improving device RF gain. Field-plate extension and passivation layer thickness were found to be parameters that can be used for trading off between device breakdown voltage and RF gain. Increasing iron-doping in the buffer layer leaded to larger breakdown voltage and RF gain but, due to the enhanced trapping effects, also to poorer large-signal operation.

GaN is an excellent wide-bandgap material for high-power electronic applications. Nowadays, lateral GaN-based transistors such as HEMT show great performance. However, HEMTs are facing several difficulties 1) the presence of a high electric field at the device surface, 2) the generation of high heat due to the high electron density along the 2D channel. To bypass most of these issues, devices with vertical architecture are a good alternative since they confine the current and the electric field in the GaN-bulk layer, which also improve the heat dissipation. In this work, we simulate a GaN MOSVFET (or vertical Fin Power FET) using Sentaurus TCAD to study its breakdown mechanism. We also investigate different design parameters to improve the RON and VBR. By optimising each parameter, a device with a positive threshold voltage of 0.7 V, a breakdown voltage as high as 1.5kV and a RON of 0.61mΩ·cm2 have been obtained.

We describe the technology and performance of integrated enhancement/depletion (E/D)-mode n++GaN/InAlN/AlN/GaN HEMTs with a self-aligned metal-oxide-semiconductor (MOS) gate structure. An identical starting epi-structure was used for both types of devices. The n++GaN cap layer was etched away in the gate trenches of the E-mode HEMT while it was left intact for the D-mode HEMT. The plasma etching process was shown to be highly selective between the cap and the InAlN barrier and also to polish the InAlN surface. Gate contacts were isolated using a dielectric layer deposited at low temperature through an e-beam resist to retain the self-aligned approach. Feasibility of the approach for future fast GaN-based mixed-signal electronic circuits was shown by obtaining alternative HEMT threshold voltage values of +0.8 V and −2.6 V, invariant maximal output current of ∼0.35 A mm−1 despite large source-to-drain distances and by demonstrating a functional logic invertor.

This work reports on large area monolithically integrated power topologies in an GaN-on-Si technology with additional on-chip sensors for improved functionality: transistors, diodes and gate-drivers together with thermal and electrical sensors are all designed and processed on a single semiconductor chip.

Excellent device performance is demonstrated by leakage currents below 0.1 µA/mm, blocking voltages well above 600 V and negligible dynamic on-state resistance increase. Operation of half-bridge chips is demonstrated in a soft-switching buck converter at switching frequencies up to 5 MHz, input voltages up to 400 V, and output power up to 250 W. This frequency-voltage combination exceeds the properties of competing semiconductor technologies like BiCMOS and hybrid GaN-on-Si by far.

The realization of such monolithic topologies in a GaN-on-Si high voltage technology opens the way towards a new generation of power devices that offer extremely high operation frequencies and functionality compared to the conventional hybrid approach.

We systematically studied the effect of different doses of 75 MeV sulfur-ion irradiation on AlInN/GaN/Si HEMT structures. The fluences range from 2.8x10^12 ions/cm2 to 5.5x10^13 ions/cm2. SRIM simulations are used to estimate ion stopping range, ion energy loss, target atom displacement, and recoiled atom distribution across active layers. Minor change in specific contact resistivity but a significant change in sheet resistance are observed upon irradiation. Transfer curves show a reduction of on-state current, gate leakage, off-state current (buffer leakage), and a positive threshold voltage shift with higher fluences as well as an increase of vertical conductivity by up to eight orders of magnitude. Positive threshold and pinch-off bias shifts are also observed in CV-characteristics, implying an enhancement of depletion width and background impurities under the gate down to the undoped GaN buffer layer. Although some degradation in performance is observed, all HEMTs remain fully functional even at highest irradiation levels.

This paper discusses a breakthrough new way to make practical electron devices utilising synthetic-diamond. The approach exploits the inherent high dielectric strength and thermal conductivity of diamond to sustain fully embedded field emission sources within the material. Advanced proofs of concept demonstrations of two devices embodying this approach have been achieved: diodes with 3V turn-on; and, vacuum electron sources with an integrated control grid and fully protected field emitters. Together these two demonstrations pave the way to an entirely new class of scalable electronic devices, that can be entirely solid-state for power electronics and high frequency amplification, for example; or, used to replace inefficient and fragile thermionic sources in vacuum electronic devices.
Two immediate space-based applications of the technology for use in travelling wave tubes and ion thrusters will be discussed, and their impact assessed.