We present a self-biased three-stage GaN-based monolithic microwave integrated circuit low-noise amplifier (LNA) operating between 26 and 29 GHz for 5G mobile communications. The self-biasing circuit, common-source topology with inductive source feedback, and RLC negative feedback loops between gate and drain of the third transistor were implemented to achieve low noise, good port match, high stability, high gain, and compact size. Measurement results show that the LNA has a high and flat gain of 30.5 ± 0.4 dB with noise figure (NF) of 1.65–1.8 dB across the band. The three-stage topology also achieves high linearity, providing the 1 dB compression point output power (P1dB) of 21 dBm in the band. To our knowledge, this combination of NF, gain, and linearity performance represents the state of art of self-biased LNA in this frequency band.

This paper presents a theoretical and experimental analysis of the capabilities of the dual-input Doherty power amplifier (DPA) architecture to mitigate efficiency and output power degradations when used in a mismatched load environment. Following a simplified linear piecewise approach, an analytical demonstration is proposed to derive optimal radio frequency drives applied to the Auxiliary path of the DPA to restore power performances while avoiding large signal voltage clipping of active cells. The proposed analytical study is corroborated with harmonic balance simulated results of a C-band, 20-W GaN DPA prototype. The fabricated dual-input DPA prototype has been measured under 1.5-VSWR mismatch configurations to validate the proposed analysis.

This paper presents the design and implementation of power amplifiers using high-power gallium nitride (GaN) high electronic mobility transistor (HEMT) powerbars and monolithic microwave integrated circuits (MMICs). The first amplifier is a class AB implementation for worldwide interoperability for microwave access (WiMAX) applications with emphasis on a low temperature cofired ceramics (LTCC) packaging solution. The second amplifier is a class S power amplifier using a high power GaN HEMT MMIC. For a 450 MHz continuous wave (CW) signal, the measured output power is 5.8 W and drain efficiency is 18.5%. Based on time domain simulations, loss mechanisms are identified and optimization steps are discussed.

With the advent of bright-blue light-emitting diodes in 1994, violet laser diodes in 1996, and vertical-cavity surface-emitting lasers at telecommunications wavelengths in 2000, all based on nitride-containing III–V compounds, a new age for optoelectronics began. Despite their technological success, III-nitride materials still hold some mysteries. Compared with conventional III–V semiconductors, even commercial nitride devices are of poor material quality. Due to their heteroepitaxial origin, their crystals are full of dislocations. Electrical properties, particularly in the case of p-type material, are fairly unsatisfactory. Still, light-emitting diodes with extremely high brightness and lasers with high power and good lifetime can be produced with III–V nitride compounds. In this review, we will give an overview of the essential properties of nitride materials for optoelectronic devices, their current development status, open questions, and recent device achievements.

Vertical-cavity surface-emitting lasers (VCSELs) based on gallium nitride semiconductor heterostructures represent a contemporary focus of research, the aim of which is to develop a new class of planar microdevices in the blue, violet, and near-ultraviolet ranges. We review recent progress in this exploratory area, to highlight the challenges and scientific excitement associated with the efforts that are under way to create flexible, short-wavelength sources for applications expected to range from biomedical diagnostics to solid-state displays and lighting.

This issue of MRS Bulletin presents a review of the progress that vertical-cavity surface-emitting lasers (VCSELs) have made throughout the wavelength spectrum. A VCSEL is a semiconductor laser diode in which light propagates normal to the epitaxial layers. In its older cousin, the Fabry—Pérot laser, light propagates in the plane of the epitaxial layers and reflects from mirrors formed by cleaving a crystal facet across the active layers. No cleaving is required for VCSEL mirrors, which are formed from multiple layers of epitaxially grown or otherwise-deposited thin films. The simple twist in the direction of the laser beam with respect to the epitaxial layers is responsible for most of the unique attributes of VCSELs, which arise from their short cavity length, their completely lithographically defined cross section, and their reliance on only wafer-scale processes for device fabrication. The articles in this issue cover a range of topics, including blue devices, short-wavelength communications lasers, recent advances in 1.3-μm VCSELs, fundamental materials issues related to distributed Bragg reflectors, theoretical quantum-well gain calculations, and work on quantum-dot VCSELs.

Discrete and coalesced monocrystalline GaN and AlxGa1−xN layers grown via pendeo-epitaxy (PE) originated from side walls of GaN seed stripes with and without SiNx top masks have been grown via organometallic vapor phase deposition on GaN/AlN/6H-SiC(0001) and GaN(0001)/AlN(0001)/3C-SiC(111)/Si(111) substrates. Scanning and transmission electron microscopies were used to evaluate the external microstructures and the distribution of dislocations, respectively. The dislocation density in the laterally grown sidewall regions and in the regions grown over the SiNx masks was reduced by at least five orders of magnitude relative to the initial GaN seed layers. Tilting of 0.2° in the coalesced GaN epilayers grown over the SiNx masks was determined via X-ray and selected area diffraction; however, tilting was not observed in the material suspended above the SiC substrate and that grown on unmasked stripes. A strong, low-temperature photoluminescence band-edge peak at ~3.45 eV with a FWHM of <300 µeV was determined on the overgrowth material grown on the silicon carbide substrates. The band-edge in the GaN grown on silicon substrates was shifted to a lower energy by 10 meV, indicative of a greater tensile stress.