IQE says that GaN power amplifiers offer superior power capability, efficiency, bandwidth and linearity compared with silicon (Si) or gallium arsenide (GaAs)-based technologies commonly used. IQE contends that GaN power amplifiers also lower overall system costs. Additionally, the company says that GaN-based low-noise amplifiers exhibit improved robustness, noise figure and dynamic range when compared to incumbent solutions. According to IQE, GaN-based transistors can operate at high temperatures, thus reducing system cost, size and weight.

IQE says that the higher cost of epitaxial material grown on 100mm SiC substrates has limited the commercial market penetration of GaN HEMTs. However, IQE says that its 150mm products are compatible with LDMOS processing lines, and its customers have demonstrated the use of LDMOS to fabricate GaN HEMTs.

Russ Wagner, VP of IQE wireless business unit said,"Scaling up to 150mm wafer diameter is a critical milestone on the path to technological maturity and wide market acceptance of GaN HEMTs on SiC." Wagner added,"We are very pleased with the quality of substrates supplied by II-VI Inc. and look forward to continuing our partnership as we execute volume production ramp and expand IQE's range of advanced high-power high-frequency transistor products for defense and wireless infrastructure applications."

The researchers note that green-emitting nitride semiconductor LED structures tend to suffer from low light output due to the difficulty in producing the high-indium-content indium gallium nitride (InGaN) needed for longer-wavelength light emission. In addition to the material quality challenge, strain induced by the lattice mismatch with pure GaN leads to large piezoelectric effects, giving electric fields that tend to pull electrons and holes apart, reducing rates of recombination into photons (i.e. the quantum-confined Stark effect, or QCSE), thus reducing quantum efficiency.

The Chinese team inserted a layer of lower-indium-content InGaN before the high-In-content light-emitting layer. Simulations suggested that such a layer could reduce the strain-dependent electric fields in the active light-emitting multiple quantum well (MQW) structure.

MOCVD on C-plane sapphire was used to produce epitaxial material with a low-In-content InGaN shallow quantum well (SQW) step. A 325nm helium-cadmium laser was used to excite the photoluminescence spectra of the materials at low temperature (85K) and room temperature (298K). One effect of the SQW was to reduce the width of the spectral peak full-width at half maximum (FWHM) at 85K from 16.7nm for the conventional LED material to 13.1nm for the SQW material. The 298K measurement reduced the conventional FWHM of 20.1nm to 15.7nm. The peak intensity was also higher with the SQW structure, therefore the SQW material had improved crystal quality.

The peak height for the SQW material at 298K was 55.1% that at 85K. The corresponding ratio for the conventional structure was 24.1%. The higher ratio for the SQW material indicates a higher rate of radiative recombination and higher internal quantum efficiency (IQE).

The electroluminescence was measured in an integrating sphere, giving light output power–current–voltage (L–I–V) results. The voltage performance is similar in the SQW and conventional devices. However, the light output at 150mA is 28.9% greater in the SQW LED (49.3mW) over the conventional device (38.4mW).

The researchers point out that improved overlap of the electron and hole wavefunctions in the device leads to improved recombination into photons. The external quantum efficiency (EQE) increased from 10.2–13.3% over the conventional LED performance.

TriQuint demonstrated its new GaN-on-diamond, high electron mobility transistors (HEMT) in conjunction with partners at the University of Bristol, Group4 Labs and Lockheed Martin under the Defense Advanced Research Projects Agency’s (DARPA) Near Junction Thermal Transport (NJTT) program. TriQuint claims that its new technology enables RF amplifiers that are up to three times smaller or up to three times the power of today’s GaN solutions.

NJTT focuses on device thermal resistance 'near the junction' of the transistor. Thermal resistance inside device structures can be responsible for more than 50% of normal operational temperature increases. TriQuint research has shown that GaN RF devices can operate at a much higher power density and in smaller sizes, through its highly effective thermal management techniques. Operating temperature largely determines high performance semiconductor reliability. It’s especially critical for GaN devices that are capable of very high power densities.

James L. Klein, vice president and general manager for infrastructure and defense products commented, “By increasing the thermal conductivity and reducing device temperature, we are enabling new generations of GaN devices that may be much smaller than today’s products. ”

Company CTO Boris Epelbaum commented, "Further diameter increase in our patented tungsten based furnaces is not limited as we are using SiC as initial seed."

Wafer polishing drastically improved as well for the AlN substrates. "The corresponding wafers feature surface roughness of less than 0.3 nm and are highly UV transparent," said Octavian Filip, director of wafering.

Dr. Mark J. Furlong, VP IQE Infrared, stated, “The opportunity to establish a new business unit with an exclusive focus on infrared materials will give IQE better opportunities to combine its substrate and epitaxial wafer products for serving a broader range of customers and even broader range of infrared device applications."

A £430,597 grant (EPSRC reference EP/K024337/1) was awarded to the University of Bath’s Department of Electronic and Electrical Engineering with principal investigator Dr DWE Allsopp joined by professor W Wang. A £393,218 grant (EPSRC reference EP/K024345/1) goes to the University of Bristol’s Department of Physics, with principal investigator professor M Kuball and professor D Cherns. IQE Silicon Compounds Ltd, NXP Semiconductors UK Ltd and Plessey Semiconductors Ltd will partner with the University of Bristol.

According to the researchers, AlGaN/GaN high electron mobility transistors (HEMTs) will enable future power conditioning applications, and be used for high efficiency military and civilian, microwave and RF systems. The researchers note that although the performance of AlGaN/GaN HEMTs presently reaches RF powers up to 40W/mm, at frequencies exceeding 300 GHz, its reliability, which is often thermally limited, is a serious issue.

The project aims to mitigate this issue through developing novel substrates that have higher heat extraction capabilities than SiC and developing low cost substrates that have improved heat extraction compared to GaN-on-silicon for more cost sensitive power electronics. The researchers assert that improvement in heat spreading will imcrease reliability and circuit efficiency and ease Gan electronics constraints.

Hitachi Cable GaN-template reportedly can solve this problem because the n-type GaN layer is already grown on the template. Hitachi Cable says that this can reduce the time required for growth by about half compared with conventional methods. The GaN-templates are also said to be suitable for high-output LEDs which require large currents because they allow both low resistance and high crystal formation,

The firm has developed single-crystal free-standing GaN substrates used for blue-violet lasers and developed HVPE-growth technology and machines for mass-production of GaN substrates. Template sized 2”, 4” and 6” are available with 8” templates in development.

“The key factor determining market growth will be how quickly GaN-on-silicon (Si) devices can achieve price parity and equivalent performance as silicon MOSFETs, insulated-gate bipolar transistors (IGBT) or rectifiers,” said Richard Eden, senior market analyst for power semiconductor discretes and modules at IHS. Eden says Price parity will be achieved in 2019, with the GaN power market passing the $1 billion mark in 2022.