A Temperature Analysis of High-power AlGaN/GaN HEMTs

Galliumnitride has become a strategic superior material for space, defense and civil applications, primarily for power amplification at RF and mm-wave frequencies. For AlGaN/GaN high electron mobility transistors (HEMT), an outstanding performance combined together with low cost and high flexibility can be obtained using a System-in-a-Package (SIP) approach. Since thermal management is extremely important for these high power applications, a hybrid integration of the HEMT onto an AlN carrier substrate is proposed. In this study we investigate the temperature performance for AlGaN/GaN HEMTs integrated onto AlN using flip-chip mounting. Therefore, we use thermal simulations in combination with experimental results using micro-Raman spectroscopy and electrical dc-analysis.Comment: Submitted on behalf of TIMA Editions (http://irevues.inist.fr/tima-editions

A Tamm plasmon-porous GaN distributed Bragg reflector cavity

This paper reports on design, measurement and optimisation of a Tamm plasmon metal-distributed Bragg reflector (DBR) cavity for use in the green part of the visible spectrum. It uses an optimised silver layer thickness and a porous DBR created using a novel electro-chemical etching technique. This device has applications in low-cost lasers, photodetectors, and photoconductive switches for the visible wavelength range

Optical properties and resonant cavity modes in axial InGaN/GaN nanotube microcavities

Microcavities based on group-III nitride material offer a notable platform for the investigation of light-matter interactions as well as the development of devices such as high efficiency light emitting diodes (LEDs) and low-threshold nanolasers. Disk or tube geometries in particular are attractive for low-threshold lasing applications due to their ability to support high finesse whispering gallery modes (WGMs) and small modal volumes. In this article we present the fabrication of homogenous and dense arrays of axial InGaN/GaN nanotubes via a combination of displacement Talbot lithography (DTL) for patterning and inductively coupled plasma top-down dry-etching. Optical characterization highlights the homogeneous emission from nanotube structures. Power-dependent continuous excitation reveals a non-uniform light distribution within a single nanotube, with vertical confinement between the bottom and top facets, and radial confinement within the active region. Finite-difference time-domain simulations, taking into account the particular shape of the outer diameter, indicate that the cavity mode of a single nanotube has a mixed WGM-vertical Fabry-Perot mode (FPM) nature. Additional simulations demonstrate that the improvement of the shape symmetry and dimensions primarily influence the Q-factor of the WGMs whereas the position of the active region impacts the coupling efficiency with one or a family of vertical FPMs. These results show that regular arrays of axial InGaN/GaN nanotubes can be achieved via a low-cost, fast and large-scale process based on DTL and top-down etching. These techniques open a new perspective for cost effective fabrication of nano-LED and nano-laser structures along with bio-chemical sensing applications

Photoluminescence evidence for silicon Frenkel defects in electron irradiated 4H SiC

The nature of defects in 4H SiC was studied by means of low temperature photoluminescence before and after energy-controlled electron irradiation. Analysis of experimental data from irradiation at energies above and below the Si displacement energy together with subsequent annealing leads to the conclusion that Si Frenkel defects have been detected experimentally in this material. Reasons why these are formed in some cases rather than carbon vacancy carbon antisite pairs are explored

Analysis of an unusual mixed-habit natural diamond by high spatial resolution techniques:Growth and fracture

Mixed-habit growth of natural diamond is relatively uncommon and the reasons why it occurs are not well-understood. The diamond studied here, unusually, alternated between cuboidal and octahedral growth over a very long period making it possible, using a variety of high resolution analytical techniques, to establish the properties of the different phases of growth. In particular, nickel, in the form of NE centres, was restricted the cuboidal regions which also contained very high levels of hydrogen. There was a high concentration of nitrogen in the sample, but photoluminescence microscopy revealed it was incorporated in the two different regions of growth in very different forms with strong N3 emission from the octahedral regions, but in the hydrogen-related 3107 cm−1 infra-red and NE centres in the cuboidal regions. These results suggest that the traditional means of assaying nitrogen levels by A- and B-centre absorption may require additions. The section of the sample studied was quite close to the nucleation of growth and study of this region by high spatial resolution photo- and cathodoluminescence microscopy revealed previously unreported aspects of this critical growth step. The experimental results also indicate that a major fracture occurred with new diamond grown between the mixed-habit and the later octahedral growth