Wide Band Gap Semiconductors

In this paper, a high efficiency C-band GaN HEMT high power amplifier with internal harmonic manipulation circuits is presented. We employed a new circuit topology for simultaneous high efficiency matching at both fundamental and 2nd-harmonic frequencies. The developed GaN HEMT amplifier has achieved over 57% drain efficiency (50% power-added-efficiency) with 100 W output power at C-band. This is the state-of-the-art efficiency of GaN HEMT high power amplifier at C-band to the best of our knowledge.

We investigate the breakdown (Vbr) enhancement potential of the field plate (FP) technique in the context of AlGaN/GaN power HEMTs. A comprehensive account of the critical geometrical and material variables controlling the field distribution under the FP is provided. A systematic procedure is given for designing a FP device, using two-dimensional (2-D) simulation, to obtain the maximum Vbr , with minimum degradation in on-resistance and frequency response. It is found that significantly higher Vbr can be achieved by raising the dielectric constant (εi) of the insulator beneath the FP. Simulation gave the following estimates. The FP can improve the Vbr by a factor of 2.8-5.1, depending on the 2-DEG concentration (ns) and εi. For n s=1×1013/cm2, the Vbr can be raised from 123 V to 630 V, using a 2.2 μm FP on a 0.8 μm silicon nitride, and 4.7 μm gate-drain separation. The methodology of this paper can be extended to the design of FP structures in other lateral FETs, such as MESFETs and LD-MOSFETs

This work reports an electron beam irradiation (30 kGy and 90 kGy) approach to narrow the band gap of the pristine CeO2 nanostructure (p-CeO2) to enhance their visible light activity through defect engineering. This was confirmed by diffuse reflectance spectroscopy, photoluminescence, Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Brunauer–Emmett–Teller, electrochemical impedance spectroscopy, and linear scan voltammetry. XPS revealed changes in the surface states, composition, Ce4+ to Ce3+ ratio, and other defects in the modified CeO2 nanostructures (m-CeO2). The m-CeO2 exhibits excellent photocatalytic activities by degrading 4-nitrophenol and methylene blue in the presence of visible light (λ > 400 nm) compared to the p-CeO2. The optical, photocatalytic, and photoelectrochemical studies and proposed mechanism further support the enhanced visible light photocatalytic activities of the m-CeO2. This study confirmed that defect-induced band gap engineered m-CeO2 could be used effectively as photocatalyst and photoelectrodes owing to their enhanced visible light photocatalytic activities.

A class-AB power amplifier was designed for an envelope tracking (ET) application. Class-AB amplifier is widely used in wireless communication systems due to the compromise between linearity and efficiency. As a power device, Cree Gallium Nitride High Electron Mobility Transistor (GaN HEMT) CGH4010F was chosen. The input and output matching networks were designed and simulated with Advanced Design System (ADS). After some optimization, the amplifier was fabricated using a Rogers RT/Duroid 5880 substrate. The amplifier together with a MAX2247 preamplifier as a driver was measured. A good agreement between the simulation and measurement results was observed. The maximum power added efficiency (PAE) is around 50 percents with the supply voltage Vsup= 10V and the maximum drain efficiency is around 75 percents with Vsup= 5V. An output power up to 42 dBm and good linearity of the output voltage with respect to the supply voltage in the range 0≪Vsup≪20V were achieved. Thus, the amplifier i...

This paper shows a physical approach to large-signal electro-thermal simulation of AlGaN/GaN HEMTs. The dynamic thermal behavior of the HEMT is described by a 3D network of thermal resistances and capacitances describing the physical structure of the HEMT, and including features such as the thermal boundary resistance between GaN and SiC, and the die-attach, as well as temperature non-uniformity along the gate finger. The thermal network is self-consistently coupled inside ADS with an electro-thermal large-signal model.

The frequency and power capability of GaN-based Gunn diodes is evaluated using transient hydrodynamic simulations. GaN Gunn oscillators with 2µm-thick GaN Gunn diodes are predicted to have fundamental frequency of 148-162GHz and power density of>10 5 W/cm 2. Due to their high frequency and power characteristics, applications of these devices are envisaged for THz signal generation.