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     

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     

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.     

Large periphery high-power AlGaN/GaN metal-oxide-semiconductorheterostructure field effect transistors on SiC with oxide-bridging

We report on AlGaN/GaN metal oxide semiconductor heterostructure field effect transistor (HFET) over SiC substrates with peripheries from 0.15 to 6 mm. These multigate devices with source interconnections were fabricated using a novel oxide-bridging approach. The saturation current was as high as 5.1 A for a 6 mm wide device with a gate leakage of 1 μA/cm² for 1.5 μm gate length in a 5 μm source-drain opening. The cutoff frequency of around 8 GHz was practically independent of the device periphery. Large-signal output rf-power as high as 2.88 W/mm was measured at 2 GHz. Both the saturation current and the rf-power scaled nearly linearly with the gate width     

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。     

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     

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.     

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.     

Influence of annealed ohmic contact metals on electron mobility of strained AlGaN/GaN heterostructures

The influence of annealed ohmic contact metals on the electron mobility of a two dimensional electron gas (2DEG) is investigated on ungated AlGaN/GaN heterostructures and AlGaN/GaN heterostructure field effect transistors (AlGaN/GaN HFETs). Current-voltage (I-V) characteristics for ungated AlGaN/GaN heterostructures and capacitance-voltage (C-V) characteristics for AlGaN/GaN HFETs are obtained, and the electron mobility for the ungated AlGaN/GaN heterostructure is calculated. It is found that the electron mobility of the 2DEG for the ungated AlGaN/GaN heterostructure is decreased by more than 50% compared with the electron mobility of Hall measurements. We propose that defects are introduced into the AlGaN barrier layer and the strain of the AlGaN barrier layer is changed during the annealing process of the source and drain, causing the decrease in the electron mobility.     

High field-effect mobility normally-off AlGaN/GaN hybrid MOS-HFET on Si substrate by selective area growth technique

The paper reports a normally-off n-channel AlGaN/GaN hybrid metal-oxide-semiconductor heterojunction field-effect transistor (MOS-HFET) on Si substrate with high field-effect mobility. To decrease the channel resistance and to improve the field-effect mobility, of the MOS-HFET, a selective area growth (SAG) technique is applied at the channel region. The fabricated MOS-HFET exhibits a good normally-off operation with the threshold voltage of 3.7 V, the specific ON-state resistance of 7.6 mΩ cm², and the breakdown voltage of over 800 V.     

High-Temperature Operation of AlGaN/GaN HFET With a Low on-State Resistance, High Breakdown Voltage, and Fast Switching

Improved characteristics of an AlGaN/GaN HFET are reported. In this paper, the authors introduce a new ohmic electrode of Ti/AlSi/Mo and a low refractive index SiN_x to decrease the contact resistance and gate leakage current. The AlGaN/GaN HFET showed a low specific resistance of 6.3 mOmega middot cm² and a high breakdown voltage of 750 V. The switching characteristics of an AlGaN/GaN HFET are investigated. The small turn-on delay of 7.2 ns, which was one-tenth of Si MOSFETs, was measured. The switching operation of the HFET showed no significant degradation up to 225 degC     

GaN/AlGaN p-channel inverted heterostructure JFET

A novel GaN/AlGaN p-channel inverted heterostructure junction field-effect transistor (HJFET) with a n/sup +/-type gate is proposed and demonstrated. A new superlattice aided strain compensation techniques was used for fabricating high quality GaN/AlGaN p-n junction. The p-channel HJFET gate leakage current was below 10 nA, and the threshold voltage was 8 V, which is close to that of typical n-channel HFETs. This new HJFET device opens up a way for fabricating nitride based complimentary integrated circuits.     

微波功率AlGaN/GaN HFET的二维能带和异质结构设计

在综述微波功率AlGaN/GaN HFET技术发展趋势基础上,提出了二维异质结能带优化设计的新课题.从自洽求解薛定谔方程和泊松方程出发研究了利用异质界面上的极化电荷来剪裁异质结能带.用极化电荷设计近矩形前势垒能增大高能热电子的隧穿势垒宽度,抑制电流崩塌.背势垒中的极化电荷强化了沟道阱的量子限制,减弱了沟道中的强场峰,能提高击穿电压和抑制电流崩塌.薄势垒层中的极化电荷强化了沟道阱的结构,降低势垒高度后能产生高密度的电子气.优化设计二维异质结构能抑制沟道中的强场峰和电流崩塌,提高击穿电压和大漏压下的输出功率.     

effect of the parameters of AlN/GaN/AlGaN and AlN/GaN/InAlN heterostructures with a two-dimensional electron gas on their electrical properties and the characteristics of transistors on their basis

The effect of the layer thickness and composition in AlGaN/AlN/GaN and InAlN/AlN/GaN transistor heterostructures with a two-dimensional electron gas on their electrical and the static parameters of test transistors fabricated from such heterostructures are experimentally and theoretically studied. It is shown that the use of an InAlN barrier layer instead of AlGaN results in a more than twofold increase in the carrier concentration in the channel, which leads to a corresponding increase in the saturation current. In situ dielectric-coating deposition on the InAlN/AlN/GaN heterostructure surface during growth process allows an increase in the maximum saturation current and breakdown voltages while retaining high transconductance.     

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.     

$hbox{HfO}_{2}$–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.     

Compact Model of Current Collapse in Heterostructure Field-Effect Transistors

In this paper, compact analytical model for the heterostructure field-effect transistor (HFET) current–voltage $(I$– $V)$ characteristics, accounting for the large-signal dispersion, also referred to as current collapse, is presented. The model is based upon an experimentally established fact that the dispersion is mainly due to carrier trapping at the source and drain sides of the gate edges. In wide-bandgap heterostructures like AlGaN/GaN, the characteristic trapping-generation times are several orders of magnitude longer than the signal period at typical operating frequencies. Thus, the radio frequency signal “sees” an averaged $I$–$V$ characteristic resulting from carrier trapping-generation. The approach, based on this difference, leads to a compact quasi-steady-state analytical model of the HFET $I$ –$V$ characteristics that can be easily implemented in device–circuit simulators. The model shows close agreement with the experimental data.      

SiO/sub 2//AlGaN/InGaN/GaN MOSDHFETs

The characteristics of a novel nitride based field-effect transistor combining SiO/sub 2/ gate isolation and an AlGaN/InGaN/GaN double heterostructure design (MOSDHFET) are reported. The double heterostructure design with InGaN channel layer significantly improves confinement of the two-dimensional (2-D) electron gas and compensates strain modulation in AlGaN barrier resulting from the gate voltage modulations. These decrease the total trapped charge and hence the current collapse. The combination of the SiO/sub 2/ gate isolation and improved carrier confinement/strain management results in current collapse free MOSDHFET devices with gate leakage currents about four orders of magnitude lower than those of conventional Schottky gate HFETs.     

含有Al组分阶变AlGaN过渡层的Si基AlGaN/GaN HEMT

采用一个AlN缓冲层和两个Al组分阶变的AlGaN过渡层作为中间层,在76.2mm Si衬底上外延生长出1.7μm厚无裂纹AlGaN/GaN异质结材料,利用原子力显微镜、X射线衍射、Hall效应测量和CV测量等手段对材料的结构特性和电学性能进行了表征。材料表面平整光滑,晶体质量和电学性能良好,2DEG面密度为1.12×1013cm-2,迁移率为1 208cm2/(V.s)。由该材料研制的栅长为1μm的AlGaN/GaN HEMT器件,电流增益截止频率fT达到10.4GHz,这些结果表明组分阶变AlGaN过渡层技术可用于实现高性能Si基GaN HEMT。     

超薄势垒InAlN/GaN HFET器件高频特性分析

采用二次外延重掺杂n+ GaN实现非合金欧姆接触,并通过优化干法刻蚀和金属有机化学气相沉积(MOCVD)外延工艺,有效降低了欧姆接触电阻.将非合金欧姆接触工艺应用于InAlN/GaN异质结场效应晶体管(HFET)器件制备,器件的有效源漏间距缩小至600 nm.同时,结合40 nm T型栅工艺,制备了高电流截止频率(fT)和最大振荡频率(fmax)的InAlN/GaN HFET器件.结果显示减小欧姆接触电阻和栅长后,器件的电学特性,尤其是射频特性得到大幅提升.栅偏压为0V时,器件最大漏源饱和电流密度达到1.88 A/mm;直流峰值跨导达到681 mS/mm.根据射频小信号测试结果外推得到器件的fT和fmax同为217 GHz.