Breakdown voltage analysis for the new RESURF AlGaN/GaN HEMTs

This paper demonstrates that the depletion process for AlGaN/GaN high electron mobility tran-sistors(HEMTs)is different than that for silicon power devices by analyzing active region depletion.Based on the special breakdown principle that occurs in AlGaN/GaN HEMTs,we propose a new reduced surface field AlGaN/GaN HEMT with a double low-density drain(LDD)and a positively charged region near the drain to optimize the surface electric field and increase the breakdown voltage.In this structure,two negative charge regions with different doses are introduced into the polarization AlGaN layer to form a double LDD and decrease the high electric field near the gate by depleting two-dimensional electron gas.A positively charged region is added to the electrode near the drain to decrease the high electric field peak at the drain edge.By applying ISE(integrated systems engineering)simulation software,we verify that the virtual gate effect occurs in the AlGaN/GaN HEMTs.The breakdown voltage is improved from 257 V in the conventional structure to 550 V in the proposed structure.     

The mobility of two-dimensional electron gas in AlGaN/GaN heterostructures with varied Al content

The mobility of the two-dimensional electron gas （2DEG） in AIGaN/GaN hetero-structures changes significantly with AI content in the AIGaN barrier layer, while few mechanism analyses focus on it. Theoretical calculation and analysis of the 2DEG mobility in AIGaN/GaN heterostructures with varied AI content are carried out based on the recently reported experimental data. The 2DEG mobility is modeled analytically as the total effects of the scattering mechanisms including acoustic deformation-potential, piezoelectric, polar optic phonon, alloy disorder, interface roughness, dislocation and remote modulation doping scattering. We show that the increase of the 2DEG density, caused by the ascension of the AI content in the barrier layer, is a dominant factor that leads to the changes of the individual scat- tering processes. The change of the 2DEG mobility with AI content are mainly determined by the interface roughness scattering and the alloy disorder scattering at 77 K, and the polar optic phonon scattering and the interface roughness scattering at the room temperature. The calculated function of the interface roughness pa- rameters on the AI content shows that the stress caused AIGaN/GaN interface degradation at higher AI content is an important factor in the limitation of the in- terface roughness scattering on the 2DEG mobility in AIGaN/GaN heterostructures with high AI content.     

新型RESURF AlGaN/GaN HEMTs器件耐压分析

本文首先从器件有源区耗尽过程分析表明AlGaN/GaN HEMTs器件具有与传统Si功率器件不同的耗尽过程,针对AlGaN/GaN HEMTs器件特殊的耐压机理,提出了一种降低表面电场,提高击穿电压的新型RESURF AlGaN/GaN HEMTs结构.新结构通过在极化的AlGaN层中引入分区负电荷,辅助耗尽二维电子气,有效降低了引起器件击穿的栅极边缘高电场,并首次在漏极附近引入正电荷使漏端高电场峰降低.利用仿真软件ISE分析验证了AlGaN/GaN HEMTs器件具有的"虚栅"效应,通过电场和击穿特性分析获得,新结构使器件击穿电压从传统结构的257V提高到550V.     

Genetic algorithm‐based neural‐network modeling approach applied to AlGaN/GaN devices

An accurate equivalent circuit large‐signal model (ECLSM) for AlGaN‐GaN high electron mobility transistor (HEMT) is presented. The model is derived from a distributed small‐signal model that efficiently describes the physics of the device. A genetic neural‐network‐based model for the gate and drain currents and charges is presented along with its parameters extraction procedure. This model is embedded in the ECLSM, which is then implemented in CAD software and validated by pulsed and continuous large‐signal measurements of on‐wafer 8 × 125‐μm GaN on SiC substrate HEMT. Pulsed IV simulations show that the model can efficiently describe the bias dependency of trapping and self‐heating effects. Single‐ and two‐tone simulation results show that the model can accurately predict the output power and its harmonics and the associated intermodulation distortion (IMD) under different input‐power and bias conditions. © 2012 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2013.     

Ultrathin GaN/AlN/GaN solution-gate field effect transistor with enhanced resolution at low source-gate voltage

The pH response of a GaN/AlN/GaN solution-gate field effect transistor (SGFET), with a GaN/AlN barrier of 7.5 nm thick, is analyzed and compared with standard GaN/AlGaN/GaN SGFETs with total barrier thicknesses of 19 and 23 nm. While all types of SGFETs show a similar surface sensitivity to H⁺ ions, a significant improvement in the transducive sensitivity of the SGFET source-drain current under pH changes is found when decreasing the barrier thickness, due to the increased transconductance of the FET structure. Resolution better than 0.005 pH can be estimated in the case of the ultrathin SGFET. Moreover, the maximum transconductance value shifts to gate-drain voltage close to 0 V, which eventually involves no need of reference electrode in less demanding applications, simplifying the final design of the device and making AlN barrier-based SGFETs highly recommended in the broad field of chemical sensors.     

A physics‐based model of DC and microwave characteristics of GaN/AlGaN HEMTs

A physics‐based model of AlGaN/GaN High Electron Mobility Transistor (HEMT) is developed for the analysis of DC and microwave characteristics. Large‐ and small‐signal parameters are calculated for a given device dimensions and operating conditions. Spontaneous and piezoelectric polarizations at the heterointerface and finite effective width of the 2DEG gas have been incorporated in the analysis. The model predicts a maximum drain current of 523 mA/mm and transconductance of 138 mS/mm for a 1 μm × 75 μm device, which are in agreement with the experimental data. © 2007 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2007.     

双轴应变下GaN有效质量的计算及其对迁移率的影响

通过计算双轴应变下氮化镓的电子能带结构,给出了GaN有效质量与应变的变化关系。在弛豫时间近似的条件下,这种关系决定了双轴应变AlGaN/GaN中二维电子气(2DEG)的迁移率的改变。在其他物理参量不变的情况下,这种二维电子气迁移率将随着张应变的增加而增加,并随着压应变的增加而减小。计算结果表明,张应变对2DEG迁移率的影响要比压应变大。此外,GaN有效质量的变化在低温时对迁移率的作用更明显。而在低温低浓度的条件下,迁移率却对有效质量的依赖很小。     

Investigation on harmonic spur characteristics of hybrid integrated LDMOS and AlGaN/GaN power amplifiers at different temperatures

The harmonic spur characteristics of a hybrid integrated S‐band power amplifier (PA), consisting of both stages of LDMOSFET and AlGaN/GaN HEMT, are studied at different temperatures. The PA offers a peak output power of 50 dBm (100 W) with power added efficiency higher than 50%, and adjacent channel power ratio performance is less than ?30 dBc. A temperature test chamber is employed for measuring the harmonic spur of PA from 233 to 393 K, and its linear response to temperature is captured at high output power level.     

Impact of ZnO gate interfacial layer on piezoelectric response of AlGaN/GaN C-HEMT based ring gate capacitor

We report on a piezoelectric response investigation of AlGaN/GaN circular high electron mobility transistor (C-HEMT) based ring gate capacitor as a new stress sensor device to be potentially applied for dynamic high-pressure sensing. A ring gate capacitor of C-HEMT with an additional ZnO gate interfacial layer was used to measure the changes in the piezoelectric charge induced directly by the variation of piezoelectric polarization of both gate piezoelectric layers (AlGaN, ZnO) for harmonic loading at different excitation frequences. Our experimental results show that about 10 nm thick piezoelectric ZnO layer grown on ring gate/AlGaN interface of C-HEMT can yield almost a 60% increase in the piezoelectric detection sensitivity of the device due to its higher piezoelectric coefficient. A three-dimensional CoventorWare simulation is carried out to confirm the increase in the measured piezoelectric response of ZnO based ring gate capacitor of C-HEMT.     

Analytical and numerical modelling of AlGaN/GaN/AlN heterostructure based cantilevers for mechanical sensing in harsh environments

Some industrial areas as oil, automotive and aerospace industries, require electromechanical systems working in harsh environments. An elegant solution is to use III-V materials alloys having semiconductor, piezoelectric and pyroelectric properties. These materials, particularly nitrides such as GaN or AlN, enable design of advanced devices suitable for harsh environment. A cantilever structure based on AlGaN/GaN/AlN heterostructures coupled with a High Electron Mobility Transistor (HEMT) can act as an electromechanical device suited for sensing applications. In this article, we present the mechanical modelling of such a structure. An analytical and a numerical model have been developed to obtain the electrical charge distribution in the structure in response to mechanical stress. A theoretical electromechanical sensitivity of 3.5 μC m⁻² was achieved for the cantilever free end displacement of several hundreds of nanometres. Both models show good agreement, presenting less than 5% deviation in almost the whole structure. The differences between the two models that are pronounced near the clamped area can be explained by particular boundary conditions of the numerical model. The topological characterization and numerical modelling allowed the estimation of the equivalent intrinsic residual stress in the structure and the stress distribution within each layer. Finally, the dynamic mechanical characterization of fabricated cantilevers using laser interferometry is presented and compared to numerical modal analysis with less than 10% deviation between theoretical and experimental resonant frequencies. The obtained results enable the use of the analytical model for further study of the electromechanical coupling with the HEMT structure.     

AlGaN/GaN C-HEMT structures for dynamic stress detection

In our work, we investigated the possibility of dynamic stress detection based on the piezoelectric polarization using AlGaN/GaN circular high electron mobility transistors (C-HEMTs). In our knowledge, stress sensors in that account are introduced for the first time. The sensor structures exhibit good linearity in the piezoelectric response under dynamic stress conditions. The measurements reveal excellent stress detection sensitivity that is independent on the measured frequency range. The sensitivity of the devices can be easily increased by increase of the area of the Schottky gate ring electrode. The further increase of the sensitivity can be tuned by an optimal selection of the DC drain and gate bias.     

Extraction of admittance parameters of symmetrically doped AlGaN/GaN/AlGaN DH-HEMT for microwave frequency applications

Microsystem Technologies - An analytical model for determining intrinsic short-circuit admittance (Y) parameters of AlGaN/GaN/AlGaN Double Heterostructure (DH) High Electron Mobility Transistor...     

Hydrogen sensing of N-polar and Ga-polar GaN Schottky diodes

N-polar and Ga-polar GaN grown on c-plane sapphire were used to fabricate platinum deposited Schottky contacts for hydrogen sensing at room temperature. After exposure to hydrogen, Ga-polar GaN Schottky barrier reduced by 3–4 meV, while the N-polar GaN Schottky contacts became fully Ohmic. The N-polar GaN Schottky diodes showed stronger and faster response to 4% hydrogen than that of Ga-polar Schottky diodes. The abrupt current increase from N-polar GaN Schottky exposure to hydrogen was attributed to the high reactivity of the N-face surface termination. The surface termination dominates the sensitivity and response time of the hydrogen sensors made of GaN Schottky diodes.     

Novel high voltage RESURF AlGaN/GaN HEMT with charged buffer layer

A novel reduced surface field (RESURF) Al GaN /GaN high electron mobility transistor(HEMT)with charged buffer layer is proposed. Its breakdown mechanism and on-state characteristics are investigated.The HEMT features buried Fluorine ions in the GaN buffer layer both under the Drift and the Gate region (FDG). The section of FDG under the drift region (FD) not only reduces the electric field (E-field) peak at the gate edge but also enhances the E-field in the drift region by the assisted depletion, leading to a significant improvement in breakdown voltage (BV). Moreover, the section of FDG under the gate (FG) enhances the back barrier and effectively prevents electron injecting from the source to form leakage current, thus a higher BV is achieved. The BV of the proposed HEMT sharply increases to 750 V from 230 V of conventional AlGaN /GaN HEMT with the same dimensional parameters, and the specific on-resistance (Ron,sp) just increases to1.21 m?·cm~2from 1.01 m?·cm~2.     

GaN管芯射频功率放大器的研究

给出了一种基于GaN管芯的C波段射频功率放大器的设计方法。该方法采用CREE公司的CGH60120D芯片,并利用ADS软件对管芯模型进行负载牵引,以得到管芯的最佳阻抗值,然后设计管芯的负载匹配电路和直流偏置电路。最后对整个电路系统进行仿真,使其达到预期的功率值。     

Direct-readout pressure sensor based on AlGaN/GaN heterostructure

Microsystem Technologies - Based on the excellent piezoelectricity of AlGaN/GaN heterostructures, a pressure sensor was fabricated combined with micro machining technology. Direct readout was...     

A simplification method for capacitance models in AlGaN/GaN high electron mobility transistors under large drain voltage using channel analysis

This article analyzes the bias dependence of gate‐drain capacitance (C_gd) and gate‐source capacitance (C_gs) in the AlGaN/GaN high electron mobility transistors under a high drain‐to‐source voltage (V_ds) from the perspective of channel shape variation, and further simplifies C_gd and C_gs to be gate‐to‐source voltage (V_gs) dependent only at high V_ds. This method can significantly reduce the number of parameters to be fitted in C_gd and C_gs and therefore lower the difficulty of model development. The Angelov capacitance models are chosen for verifying the effectiveness of simplification. Good agreement between simulated and measured small‐signal S‐parameters, large‐signal power sweep, and power contours comprehensively proves the accuracy of this simplification method.     

Surface‐treatment effects of a sapphire substrate by He+‐, Ar+‐, and Xe+‐ion implantations for GaN epitaxial layers

Abstract— The structural, electrical, and optical properties of GaN epilayers grown on various ion‐implanted sapphire(0001) substrates by MOCVD were investigated. GaN or AlN buffer layers and pre‐treatment were indispensably introduced before GaN‐epilayer growth. The ion‐implanted substrate's surface had decreased internal free energies during the growth of the ion‐implanted sapphire(0001) substrates. The crystal and optical properties of the GaN epilayers grown in ion‐implanted sapphire(0001) substrates were improved. Also, an excessively roughened and modified surface caused by ions degraded the GaN epilayers. Not only the ionic radius but also the chemical species of implanted sapphire(0001) substrates improved the properties of the GaN epilayers grown by MOCVD. It is obvious that the ion‐implanted pre‐treatment of sapphire(0001) substrates can be an alternative pre‐treatment procedure for GaN deposition and has the potential to improve the properties of the GaN epilayers on sapphire(0001) substrates.     

Differential evolution based small signal modeling of GaN HEMT

In this article differential evolution based method of small signal modeling of GAN HEMT has been investigated. The method uses a unique search space exploration strategy to obtain optimized values of intrinsic and extrinsic elements pertaining to compact small signal model from extracted equivalent circuit elements and measured S‐parameter data. Effectiveness of the method has been illustrated by comparing the measured S‐parameter data of a 4 × 0.1 × 75 μm² GaN/SiC HEMT in the frequency range of 1 to 30 GHz wherein modeled and measured data are in good agreement.     

Growth and characterization of 0.8-μm gate length AlGaN/GaN HEMTs on sapphire substrates

AlGaN/GaN high electron mobility transistor (HEMT) structures were grown on 2 inch sapphire substrates by MOCVD, and 0.8-μm gate length devices were fabricated and measured. It is shown by resistance mapping that the HEMT structures have an average sheet resistance of approximately 380 Θ/sq with a uniformity of more than 96%. The 1-mm gate width devices using the materials yielded a pulsed drain current of 784 mA/mm atV _gs=0.5 V andV _ds=7 V with an extrinsic transconductance of 200 mS/mm. A 20-GHz unity current gain cutoff frequency (f _T) and a 28-GHz maximum oscillation frequency (f _max) were obtained. The device with a 0.6-mm gate width yielded a total output power of 2.0 W/mm (power density of 3.33 W/mm) with 41% power added efficiency (PAE) at 4 GHz.