Future of GaN RF Technology in Europe
In the last years GaN has remained a key technology in Europe in particular, but not only, for RF Applications. After an intensive period of research and development the scope has shifted towards industrialization and product development. This is especially true for the applications up to around 20GHz where systems are now being built using European GaN-based components. At the same time, an increasing part of the research activity has moved toward higher frequencies beyond 20GHz.
Evaluation of an InAlN/AlN/GaN HEMT with Ta-based ohmic contacts and PECVD SiN passivation
An InAlN/AlN/GaN HEMT with Au-free Ta-based ohmic contacts and a high-quality PECVD SiN passivation is reported. The ohmic contacts were annealed at 550 degrees C, resulting in a contact resistance of 0.64 Omm. The gate length was 50 nm. The device performance and the process were evaluated by performing DC-, pulsed IV-, RF-, and load-pull measurements. It was observed that current slump was effectively mitigated by the passivation layer. The DC channel current density increased by 71 % to 1170 mA/mm at the knee of the IV curve, and the transconductance increased from 382 to 477 mS/mm after passivation. At the same time the gate leakage increased, and the extrinsic f(max) decreased from 207 to 140 GHz. Output powers of 4.1 and 3.5 W/mm were measured after passivation at 31 and 40 GHz, respectively.
Recent progress in engineering near-infrared persistent luminescence nanoprobes for time-resolved biosensing/bioimaging
Persistent luminescence nanoprobes (PLNPs) can remain luminescent after ceasing excitation. Due to the ultra-long decay time of persistent luminescence (PersL), autofluorescence interference can be efficiently eliminated by collecting PersL signal after autofluorescence decays completely, thus the imaging contrast and sensing sensitivity can be significantly improved. Since near-infrared (NIR) light shows reduced scattering and absorption coefficient in penetrating biological organs or tissues, near-infrared persistent luminescence nanoprobes (NIR PLNPs) possess deep tissue penetration and offer a bright prospect in the areas of in vivo biosensing/bioimaging. In this review, we firstly summarize the design of different types of NIR PLNPs for biosensing/bioimaging, such as transition metal ions-doped NIR PLNPs, lanthanide ions-doped NIR PLNPs, organic molecules-based NIR PLNPs, and semiconducting polymer self-assembled NIR PLNPs. Notably, organic molecules-based NIR PLNPs and semiconductor self-assembled NIR PLNPs, for the first time, were introduced to the review of PLNPs. Secondly, the effects of different types of charge carriers on NIR PersL and luminescence decay of NIR PLNPs are significantly emphasized so as to build up an in-depth understanding of their luminescence mechanism. It includes the regulation of valence band and conduction band of different host materials, alteration of defect types, depth and concentration changes caused by ion doping, effective radiation transitions and energy transfer generated by different luminescence centers. Given the design and potential of NIR PLNPs as long-lived luminescent materials, the current challenges and future perspective in this rapidly growing field are also discussed.