The transition time of microwave GaN HEMT series switch transistors is evaluated. Different GaN HEMT technologies are studied, and e.g. technologies assumed to have an Fe-doped buffer, a slow recovery is observed, and the level has still not recovered to the steady state case after 40ms. The amplitude of the transient increases slightly with more negative off bias, and a significant impact on the amplitude related to the on-bias is observed (Vg < 0V). This is very relevant for user cases where 0V Vg might not be possible to achieve. However, a positive gate bias reduces the impact of the slow transient. Furthermore, a strong temperature dependence of the transient can be seen and the transition speed is increasing at higher operating temperatures, which is in line with trap related slow transients.

For future high frequency applications requiring shorter gate length of 100 nm and below, the electric field peak at the gate vicinity is extremely high, resulting in a more pronounced self-heating also at lower drain bias (VDS ≤ 15 V for instance). Theoretically, a thin nucleation layer with an outstanding quality would be enough to accommodate the growth of high quality GaN HEMTs avoiding the use of a complex stack and thus enhancing significantly the thermal dissipation. Recently, the company SweGaN demonstrated the growth of a buffer-free AlGaN/GaN heterostructure using solely a thin AlN nucleation layer (NL) with a thickness well-below 100 nm. In this work, this novel technology is assessed by applying a variation of short gate lengths starting from 250 nm down to below 100 nm in the same mask-set. Corresponding DC and RF electrical characterizations will be presented.

Mechanical stress in the active epitaxial layers of GaN field effect transistors significantly influences channel electron concentration. This effect has now been utilized to tailor device properties by intentionally applying mechanical strain to the channel region underneath the gate. The strained channel layers are a consequence of either a mechanically stressed SiNx passivation film, gate electrode or the superposition of both. Physical device simulations in conjunction with experimental verifications have demonstrated controllable device threshold voltage variations within a range of several volts at a given basic epitaxial layer design. This means that dedicated variations in the GaN MMIC device process can be introduced for obtaining certain functionalities or performance. Therefore this new technique opens interesting aspects for further developments of mm-wave GaN MMICs such as optimized power transistors with low loss access regions, the monolithic integration of devices with different functionalities (e.g. power and low-noise device) and many other aspects.

(In)AlGaN LEDs emitting in the UVB and the UVC wavelength regions are of tremendous interest due to their various applications such as phototherapy, sensing of gases (e.g., SO2, NOx, NH3), disinfection of water, air and surfaces, non-line-of-sight communication and basic science experiments in the area of gravitational sensors. In this paper, we present the fabrication of (In)AlGaN LEDs emitting from 320nm to 230nm. The LEDs were grown by MOVPE on sapphire substrates. By optimizing the LED heterostructure design, growth parameters and the processing and packaging technologies, significant progress was achieved with respect to the internal efficiency, injection efficiency and light extraction. Based on these optimizations, UVB LEDs, emitting at 310nm, were realized with up to 30mW output powers at 350mA and lifetime (L50), after 100h of burn-in, of 8000h. Furthermore, UVC LEDs, with single emission peak at 233nm and output powers of 300µW at 100mA will also be presented.

Gallium-Nitride-based MicroLED arrays of individually-addressable LED pixels offer advantages over conventional LEDs such as extremely high modulation bandwidths and spatially and temporally controllable illumination patterns. Further miniaturization will enable the use of such LED arrays as a basis for novel imaging and sensing techniques. In this work, microLED arrays with pixel dimensions and pitches down to 2 microns were designed and fabricated by top-down manufacturing methods. Technological details of this will be presented. The microLED arrays were then transferred via flip-chip to PCBs including the driver circuit and their brightness and modulation speed were investigated. Moreover, the characteristics of even smaller LED pixels were explored and cathodoluminescence and electroluminescence characteristics of small light sources with dimensions of < 1 µm were extracted.