Switching Characteristics of GaN HFETs in a Half Bridge Package for High Temperature Applications

AlGaN/GaN heterojunction field effect transistors (HFETs) are expected to be a good candidate for power switching application at high temperatures. We designed and fabricated a discrete HFET package and a half bridge module using the AlGaN/GaN HFETs and SiC Schottky barrier diodes (SBDs) for high temperature applications. The half bridge module exhibited good reliability after 250 C and 400 h high temperature storage. Switching characteristics of the AlGaN/GaN HFET were investigated. Qg x Ron, which shows a figure of merit of switching operation, was more than 10 times better than commercial Si MOSFETs. The switching characteristics of the HFET showed no significant degradation up to 225 C.     

Dynamic model of AlGaN/GaN HFET for high voltage switching

We analyze the channel and surface charge dynamics of a high voltage AlGaN/GaN Heterostructure Field Effect Transistor (HFET) operating as a power switch. We demonstrate that operation in the voltage range exceeding 100 V without field plates involves alternating of the surface compensating charge in the gate-drain spacing. Developed model predicts the switching speed limitation of power HFET determined by the surface recharge rate and provides new, voltage-scalable design approach of AlGaN/GaN power devices.     

AlGaN/GaN异质结构欧姆接触的研制

研究了 Ga N高温宽禁带半导体外延层上欧姆接触的制备工艺 ,讨论了几种测试方法的优缺点 ,并根据器件制作的工艺兼容性 ,在 n-Ga N样品上获得了 4× 1 0 - 6 Ω·cm2的欧姆接触 ,在 Al Ga N/Ga N异质结构样品上获得了 4× 1 0 - 4Ω· cm2 的欧姆接触。实验结果表明 ,Al Ga N/Ga N上低阻欧姆接触的制备及其工艺兼容性是Ga N HFET器件研制的技术难点     

Improved RF modeling techniques for enhanced AlGaN/GaN HFETs

Modeling procedures of an AlGaN/GaN HFET that incorporate the effects of both a GaN cap layer and an AlN sub-buffer layer are presented. A single off-state measurement method to extract all eight parasitic elements of an enhanced HFET has been successfully applied. In addition, procedures to model the nonlinear drain-to-source current characteristics featuring a kink are described.     

AlGaN/GaN metal oxide semiconductor heterostructure field effecttransistor

We report on the AlGaN/GaN metal oxide semiconductor heterostructure field effect transistor (MOS-HFET) and present the results of the comparative studies of this device and a base line AlGaN/GaN heterostructure field effect transistor (HFET). For a 5-μ source-to-drain opening, the maximum current was close to 600 mA/mm for both devices. The gate leakage current for the MOS-HFET was more than six orders of magnitude smaller than for the HFET     

The 1.6-kV AlGaN/GaN HFETs

The breakdown voltages in unpassivated nonfield-plated AlGaN/GaN HFETs on sapphire substrates were studied. These studies reveal that the breakdown is limited by the surface flashover rather than by the AlGaN/GaN channel. After elimination of the surface flashover in air, the breakdown voltage scaled linearly with the gate–drain spacing reaching 1.6 kV at 20$muhboxm$. The corresponding static ON-resistance was as low as 3.4$hboxmOmega cdot hboxcm^2$. This translates to a power device figure-of-merit$V_ BR^2/R_ ON = hbox7.5times hbox10^8 hboxV^2 cdot Omega^-1 hboxcm^-2$, which, to date, is among the best reported values for an AlGaN/GaN HFET.     

AlGaN/GaN HFET的2DEG和电流崩塌研究(Ⅰ)

从不同的视角回顾和研究了A1GaN/GaN HFET的二维电子气(2DEG)和电流崩塌问题.阐述了非掺杂的AIGaN/GaN异质结界面存在2DEG的原动力是极化效应,电子来源是AlGaN上的施主表面态.2DEG浓度与AlGaN/GaN界面导带不连续性、AlGaN层厚和Al组分有密切关系.揭示了AlGaN/GaN HFET的2DEG电荷涨落受控于表面、界面和缓冲层中的各种缺陷及外加应力,表面空穴陷阱形成的虚栅对输入信号有旁路和延迟作用,它们导致高频及微波状态下的电流崩塌.指出由于构成电流崩塌因素的复杂性,各种不同的抑制电流崩塌方法都存在不足,因此实现该器件大功率密度和高可靠性还有很长的路要走.     

An Al0.3Ga0.7N/GaN undoped channelheterostructure field effect transistor with Fmax of 107 GHz

An Al_0.3Ga_0.7N/GaN heterostructure field effect transistor (HFET) grown on semi-insulating SiC with an 0.2-μm gate length is reported. A source-drain ohmic contact resistance of 0.15-Ω-mm was achieved through the use of high Al content and high n-type doping (1E19 cm^-3) in the AlGaN donor layer and optimized metallization procedures. We obtained a maximum transconductance of 260 mS/mm, a saturated current density of 1.2 A/mm, and a maximum oscillation frequency in excess of 107 GHz in the devices. The results are one of the best achieved up to now, and they will open up the potential for the applications of AlGaN/GaN HFET's in high-power microwave radar, remote sensing, and communications     

Characterization and modeling of AlGaN/GaN MOS capacitor with leakage for large signal transistor modeling

Dual mode AlGaN/GaN metal oxide semiconductor (MOS) heterostructure field-effect transistor (HFET) devices were fabricated and characterized. In HFET mode of operation the devices showed an f/sub t//spl middot/L/sub g/ product of 12GHz/spl middot//spl mu/m at Vgs=-2 V. The AlGaN devices showed formation of an accumulation layer under the gate in forward bias and a f/sub t//spl middot/L/sub g/ product of 6GHz/spl middot//spl mu/m was measured at Vgs=5 V. A novel piecewise small signal model for the gate capacitance of MOS HFET devices is presented and procedures to extract the capacitance in presence of gate leakage are outlined. The model accurately fits measured data from 45MHz to 10GHz over the entire bias range of operation of the device.     

Theoretical Study of Electron Confinement in Submicrometer GaN HFETs Using a Thermally Self-Consistent Monte Carlo Method

This paper studies various existing advanced GaN heterostructures, which are introduced to provide better confinement of the 2-D electron gas in the channel using a Monte Carlo simulation method coupled with a 3-D solution of the heat diffusion equation. It is shown that the introduction of acceptors in the buffer layer and the introduction of an InGaN back-barrier layer at the bottom of the channel, in a single heterojunction AlGaN/GaN heterostructure field-effect transistor (HFET), improve charge confinement in the channel. It is also shown how the inclusion of an AlGaN carrier exclusion layer at the AlGaN/GaN interface significantly improves the current-handling capability of the HFET. This paper is also a study of the effect of carrier confinement on the thermal performance of each structure; the results show that better confinement of carriers in the HFET channel is accompanied by an enhancement of the influence of self-heating effects.     

AlGaN/GaN heterostructure field-effect transistor model includingthermal effects

A new AlGaN/GaN heterostructure field-effect transistor (HFET) model, in the framework of the gradual channel approximation and based on Monte Carlo simulations of the electron transport properties, is presented. The effects on the dc HFET output characteristics arising from contact resistances, from the ungated access channels between the gate and the source and between the gate and the drain, and from self-heating are analyzed. By examining the channel potential, the ungated regions are shown to have nonlinear characteristics. The solution method uses implicit analytical relationships for the current in the gated and ungated segments of the channel that are connected by matching boundary conditions. Thermal effects on the transport parameters associated with self-heating are included self-consistently. The model results are in very good agreement with experimental data from AlGaN/GaN HFETs fabricated on sapphire substrates. The model also identifies several device design parameters that need to be adjusted to obtain optimized performance in terms of output current and transconductance     

$hbox{HfO}_{2}$–III-Nitride RF Switch With Capacitively Coupled Contacts

We report on the first metal-oxide-semiconductor AlGaN/GaN radio-frequency (RF) switch with capacitively coupled contacts using a HfO₂ layer as the gate dielectric and surface passivation layer. The new insulating-gate RF switch has a lower leakage current and can handle higher RF powers than AlGaN/GaN HFET switches.     

GaN基HFET的新进展

回顾了氮化镓 ( Ga N)基异质结场效应晶体管 ( HFET)的发展 ,概述了它的直流和微波特性。制作氮化镓基 HFET可以采用不同的器件结构 ,不同的结构有各自的优点 ,对器件性能有很大影响。多数器件采用了其中两种比较成熟的结构 ,文中对这两种结构进行了讨论     

Recessed-gate AlGaN/GaN HFETs with lattice-matched InAlGaN quaternary alloy capping layers

In this paper, we present recessed AlGaN/GaN heterojunction field-effect transistors (HFETs) with lattice-matched InAlGaN capping layers, which reduce both ohmic contact resistance and series resistance between the AlGaN and the capping layer. The lattice-matched alloy epitaxial layer with both In and Al high compositions are successfully grown by metal-organic chemical vapor deposition. The grown lattice-matched In/sub 0.09/Al/sub 0.32/Ga/sub 0.59/N capping layer has close total polarization and bandgap to those of the underlying Al/sub 0.26/Ga/sub 0.74/N layer. The balanced polarization eliminates the depletion of electrons at the In/sub 0.09/Al/sub 0.32/Ga/sub 0.59/N/Al/sub 0.26/Ga/sub 0.74/N interface, which can reduce the series resistance across it. It is also noted that the fabricated HFET exhibits very low ohmic contact resistance of 1.0/spl times/10/sup -6/ /spl Omega//spl middot/cm/sup 2/ or less. Detailed analysis of the source resistance reveals that the series resistance at the In/sub 0.09/Al/sub 0.32/Ga/sub 0.59/N/Al/sub 0.26/Ga/sub 0.74/N interface is one fifth as low as the resistance at the conventional GaN/Al/sub 0.26/Ga/sub 0.74/N interface.     

GaN HFET的性能退化

在综述大功率AlGaN/GaN HFET性能退化实验结果的基础上,研究了器件退化与电流崩塌间的关联。分析了现有各类器件失效模型的优点和不足之处。通过沟道中强电场和热电子分布的研究,完善了热电子触发产生缺陷陷阱的器件退化模型。使用这一模型解释了实验中观察到的各类性能退化现象,指出优化设计异质结构可以有效减弱GaN HFET的性能退化。最后提出减弱器件性能退化的方法和途径。     

Structural properties of alloyed Ti/Al/Ti/Au and Ti/Al/Mo/Au ohmic contacts to AlGaN/GaN

Two alloyed ohmic contact structures for AlGaN/GaN–Ti/Al/Ti/Au and Ti/Al/Mo/Au were studied. Both structures were optimized for minimum ohmic contact resistance. Structures grown on sapphire and SiC substrates were used to investigate structural properties of ohmic contacts to AlGaN/GaN. Ohmic contacts to AlGaN/GaN on SiC showed higher contact resistance values compared to contacts to AlGaN/GaN on sapphire. Ohmic contact metals were etched on samples after annealing. The alloyed interface was studied with backside illumination under an optical microscope. Alloyed inclusions associated with threading dislocations were observed on the surface. For the AlGaN/GaN on SiC sample the inclusion density was an order of magnitude lower than for the sample on sapphire. Conductive atomic force microscopy with carbon nanotube tip was used to investigate topography and conductivity profile of the surface after ohmic contact metal removal by etching.     

三种纵向结构的AlGaN/GaN HFET性能比较

对AlGaN/GaN HFET纵向的常规结构、倒置结构和双异质结进行了研究，结果表明：常规结构的材料生长简单、容易控制，倒置结构的直流性能低于常规结构，而双异质结虽然在材料生长方面较为复杂，但它可以获得较常规结构更为优良的直流特性.     

高跨导AlGaN/GaN HFET器件研究

报道了蓝宝石衬底上AlGaN/GaNHFET的制备以及室温下器件的性能。器件栅长为0.8μm,源漏间距为3μm,得到器件的最大漏电流密度为0.7A/mm,最大跨导为242.4mS/mm,截止频率(fT)和最高振荡频率(fmax)分别为45GHz和100GHz。同时器件的脉冲测试结果显示,SiN钝化对大栅宽器件的电流崩塌效应不能彻底消除。     

AlGaN/GaN power HFET on silicon substrate with source-via grounding (SVG) structure

We have developed a high-power AlGaN/GaN HFET fabricated on 4-in conductive Si substrate with a source-via grounding (SVG) structure. The SVG structure enables efficient chip layout and high packing density by the vertical configuration. By establishing a high-quality epitaxial technology on a Si substrate and by significantly reducing the parasitic resistance, a very low specific on-state resistance of 1.9 m/spl Omega//spl middot/cm/sup 2/ is achieved. The breakdown voltage is as high as 350 V, which is attributed to the Si substrate acting as a backside field plate. Because of reduction of the parasitic inductance, very high level of current (2.0 kA/cm/sup 2/) transients, i.e., a turn-on time of 98 ps and a turn-off time of 96 ps, are successfully measured for the first time.     

Low flicker-noise GaN/AlGaN heterostructure field-effecttransistors for microwave communications

We report a detailed investigation of flicker noise in novel GaN/AlGaN heterostructure field-effect transistors (GaN HFET). Low values of 1/f noise found in these devices (i.e., the Hooge parameter is on the order of 10^-1) open up the possibility for applications in communication systems. We have examined the scaling of the noise spectral density with the device dimensions in order to optimize their performance. It was also found that the slope γ of the 1/f^γ noise density spectrum is in the 1.0-1.3 range for all devices and decreases with the decreasing (i.e., more negative) gate bias. The results are important for low-noise electronic technologies requiring a low phase-noise level