AlGaN/GaN high electron mobility transistors on semi-insulating bulk ammonothermal GaN have been investigated. By application of regrown ohmic contacts, the problem with obtaining low resistance ohmic contacts to low-dislocation high electron mobility transistor (HEMT) structures was solved. The maximum output current was about 1 A/mm and contact resistances was in the range of 0.3–0.6 $\Omega$ ·mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.

Thermal characterization of modern microwave power transistors such as high electron-mobility transistors based on gallium nitride (GaN-based HEMTs) is a critical challenge for the development of high-performance new generation wireless communication systems (LTE-A, 5G) and advanced radars (active electronically scanned array (AESA)). This is especially true for systems operating with variable-envelope signals where accurate determination of self-heating effects resulting from strong- and fast-changing power dissipated inside transistor is crucial. In this work, we have developed an advanced measurement system based on DeltaV_GS method with implemented software enabling accurate determination of device channel temperature and thermal resistance. The methodology accounts for MIL-STD-750-3 standard but takes into account appropriate specific bias and timing conditions. Three types of GaN-based HEMTs were taken into consideration, namely commercially available GaN-on-SiC (CGH27015F and TGF2023-2-01) and GaN-on-Si (NPT2022) devices, as well as model GaN-on-GaN HEMT (T8). Their characteristics of thermal impedance, thermal time constants and thermal equivalent circuits were presented. Knowledge of thermal equivalent circuits and electro–thermal models can lead to improved design of GaN HEMT high-power amplifiers with account of instantaneous temperature variations for systems using variable-envelope signals. It can also expand their range of application.

Power amplifiers applied in modern active electronically scanned array (AESA) radars and 5G radios should have similar features, especially in terms of phase distortion, which dramatically affects the spectral regrowth and, moreover, they are difficult to be compensated by predistortion algorithms. This paper presents a GaN-based power amplifier design with a reduced level of transmittance distortions, varying in time, without significantly worsening other key features such as output power, efficiency and gain. The test amplifier with GaN-on-Si high electron mobility transistors (HEMT) NPT2018 from MACOM provides more than 17 W of output power at the 62% PAE over a 1.0 GHz to 1.1 GHz frequency range. By applying a proposed design approach, it was possible to decrease phase changes on test pulses from 0.5° to 0.2° and amplitude variation from 0.8 dB to 0.2 dB during the pulse width of 40 µs and 40% duty cycle.

The paper presents the results of a project leading to design and fabrication of a transmitting-receiving module destined for application in an active electronically scanned array (AESA). The module is supposed to operate in the band from 9 GHz to 10 GHz. GaAs technology core chip is applied and it is used to drive power amplifiers based on GaN technology. The shape of the module enclosure follows the requirements of limited space available in an X-band AESA.

The substrate of choice for high power microwave GaN-based devices is silicon carbide. However recently novel semi-insulating truly bulk GaN substrates with excellent crystalline and electrical parameters have been developed by Ammono S..A. These allow to elaborate AlGaN/GaN heterostructures with high electron mobility values and density of two-dimensional electron gas. Developed processing steps, especially planar isolation by ion implantation and formation of low resistivity regrown ohmic contacts enabled fabrication of high quality devices. An 1000 mA/mm on-state current density along with low 4.4 Ω/mm on-state resistance were achieved. For the devices with rectangular, 0.8 μm gate length the f_MAG and f_s were 31 GHz and 22 GHz. The maximum output power density was more than 4.15 W/mm in S-band.