GaAs基InAs/AlSb二维电子气结构的生长优化（英文）

采用分子束外延设备(MBE),外延生长了InAs/AlSb二维电子气结构样品.样品制备过程中,通过优化AlGaSb缓冲层厚度和InAs/AlSb界面厚度、改变AlSb隔离层厚度,分别对比了材料二维电子气特性的变化,并在隔离层厚度为5nm时,获得了室温电子迁移率为20500cm~2/V·s,面电荷密度为2.0×1012/cm~2的InAs/AlSb二维电子气结构样品,为InAs/AlSb高电子迁移率晶体管的研究和制备提供了参考依据.     

HEMT太赫兹探测器的二维电子气特性分析

采用分子束外延技术(MBE)对GaAs/Al_xGa_(1-x)As二维电子气(2DEG)样品进行了制备,样品制备过程中,通过改变Al的组分含量、隔离层厚度、对比体掺杂与δ掺杂两种方式,在300 K条件下对制备的样品进行了霍尔测试,获得了室温迁移率7.205E3cm~2/Vs,载流子浓度为1.787E12/cm~3的GaAs/Al_xGa_(1-x)As二维电子气沟道结构,并采用Mathematica软件分别计算了不同沟道宽度时300 K、77 K温度下GaAs基HEMT结构的太赫兹探测响应率,为HEMT场效应管太赫兹探测器的研究和制备提供了参考依据.     

MBE生长高2-DEG面密度InP基PHEMT外延材料

利用MBE技术生长了InP基InAlAs/InGaAs PHEMT结构,使用原子力显微镜(AFM)、霍耳测试系统研究了影响二维电子气(2-DEG)面密度和电子迁移率的因素,着重分析了隔离层厚度、沟道层In组分的影响.在保持较高迁移率的基础上,生长出了高μn×ns的InP PHEMT外延材料.     

RF-MBE生长的AlGaN/GaN高电子迁移率晶体管特性

用射频分子束外延技术研制出了室温迁移率为1035cm2/(V·s),二维电子气浓度为1.0×1013cm-2,77K迁移率为2653cm2/(V·s),二维电子气浓度为9.6×1012cm-2的AlGaN/GaN高电子迁移率晶体管材料.用此材料研制的器件(栅长为1μm,栅宽为80μm,源-漏间距为4μm)的室温非本征跨导为186mS/mm,最大漏极饱和电流密度为925mA/mm,特征频率为18.8GHz.     

RF-MBE生长的AlGaN/GaN高电子迁移率晶体管特性

用射频分子束外延技术研制出了室温迁移率为10 35 cm2 /(V·s) ,二维电子气浓度为1.0×10 1 3cm- 2 ,77K迁移率为2 6 5 3cm2 /(V·s) ,二维电子气浓度为9.6×10 1 2 cm- 2 的Al Ga N/Ga N高电子迁移率晶体管材料.用此材料研制的器件(栅长为1μm,栅宽为80μm,源-漏间距为4μm )的室温非本征跨导为186 m S/m m,最大漏极饱和电流密度为92 5 m A/m m,特征频率为18.8GHz.     

GaAs PHEMT材料中2DEG浓度的控制与测试研究

设计并使用分子束外延(MBE)方法制备了不同帽层厚度、不同掺杂浓度的双平面掺杂GaAs PHEMT外延材料,采用不同工艺手段控制InGaAs沟道异质结界面的平滑程度。采用非接触霍尔方法对样品二维电子气(2DEG)浓度及迁移率进行测试,并用范得堡法对实验结果加以验证。结果表明,平整异质结界面生长技术能有效控制高迁移率2DEG浓度分布;与范德堡法相比,非接触霍尔方法无破坏性、测试结果可靠,该结果可以用来分析多层结构的PHEMT外延材料中InGaAs沟道界面的生长情况。     

MOCVD生长的SiC衬底高迁移率GaN沟道层AlGaN/AlN/GaN HEMT结构

用MOCVD技术在高阻6H-SiC衬底上研制出了具有高迁移率GaN沟道层的AlGaN/AlN/GaN高电子迁移率晶体管(HEMT)结构材料,其室温和80K时二维电子气迁移率分别为1944和11588cm2/(V·s),相应二维电子气浓度为1.03×1013cm-2;三晶X射线衍射和原子力显微镜分析表明该材料具有良好的晶体质量和表面形貌,10μm×10μm样品的表面粗糙度为0.27nm.用此材料研制出了栅长为0.8μm,栅宽为1.2mm的HEMT器件,最大漏极饱和电流密度和非本征跨导分别为957mA/mm和267mS/mm.     

RF-MBE生长AlN/GaN超晶格结构二维电子气材料

用射频等离子体辅助分子束外延技术( RF- MBE)在c面蓝宝石衬底上外延了高质量的Ga N膜以及Al N/Ga N超晶格结构极化感应二维电子气材料.所获得的掺Si的Ga N膜室温电子浓度为2 .2e1 8cm- 3,相应的电子迁移率为2 2 1cm2 /( V·s) ;1μm厚的Ga N外延膜的( 0 0 0 2 ) X射线衍射摇摆曲线半高宽( FWHM)为7′;极化感应产生的二维电子气室温电子迁移率达到10 86cm2 /( V·s) ,相应的二维电子气面密度为7.5e1 2 cm- 2 .     

GaAs基单片集成InGaP／AIGaAs／InGaAs增强／耗尽型PHEMTs

提出了一种新结构单片集成增强/耗尽型(E/D)InGaP/AlGaAs/InGaAs赝配高电子迁移率晶体管(PHEMTs).外延层材料通过分子束外延技术生长,在室温下,其电子迁移率和二维电子气浓度分别为5410cm2/(V·s)和1.34×1012cm-2.首次提出了普通光学接触曝光分步制作增强与耗尽型的栅技术方法.研制出了单片集成E/D型PHEMTs,获得良好的直流和交流特性,最大饱和漏电流密度分别为300和340mA/mm,跨导为350和300mS/mm,阈值电压为0.2和-0.4V,增强型的fT和fmax为10.3和12.4GHz,耗尽型的fT和fmax为12.8和14.7GHz.增强/耗尽型PHEMTs的栅漏反向击穿电压都为-14V.     

InP-HEMT中复合沟道的设计与生长

设计并生长了带有复合沟道的InP基HEMT材料,该材料具有较高的二维电子气浓度和迁移率。在使用In_xGa_(1-x)As/In_(0.53)Ga_(0.47)As复合沟道时,当In组分等于0.7时得到较好的沟道输运性能;在使用InAs复合沟道时,得到了二维电子气浓度为2.3×10~(12)/cm~2、室温迁移率高达13600 cm~2/V·s的性能优良的HEMT材料。     

InP基功率HEMT结构材料分子束外延生长研究

从 3个层面研究了分子束外延 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P功率 HEMT结构材料生长技术。首先 ,通过观察生长过程的高能电子衍射 (RHEED)图谱 ,确立了 Ga0 .47In0 .53As/ In P结构表面层的 MBE RHEED衍射工艺相图 ,据此生长的单层 Si-doped Ga0 .47In0 .53As(40 0 nm) / In P室温迁移率可达 6960 cm2 / V· s及电子浓度 1 .3 3 E1 7cm- 3。其次 ,经过优化结构参数 ,低噪声 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In P HEMT结构材料的 Hall参数达到μ30 0 K≥ 1 0 0 0 0 cm2 / V· s、2 DEG≥ 2 .5 E1 2 cm- 2 。最后 ,在此基础之上 ,降低 spacer的厚度、在 Ga0 .47In0 .53As沟道内插入 Si平面掺杂层并增加势垒层的掺杂浓度获得了功率 Al0 .48In0 .52 As/ Ga0 .47In0 .53As/ In PHEMT结构材料 ,其 Hall参数达到μ30 0 K≥ 80 0 0 cm2 / V· s、2 DEG≥ 4 .0 E1 2 cm- 2 。     

Dependence of electron mobility on spacer thickness and electron density in modulation-doped Ga0.47In0.53As/Al0.48In0.52As heterojunctions

Modulation-doped Ga0.47In0.53As/Al0.48In0.52As heterojunctions were grown by molecular beam epitaxy. Electron mobilities were measured at room temperature and 77 K as a function of undoped Al0.48In0.52As spacer layer thickness and sheet carrier concentration. Enhanced mobilities were as high as 10 900 cm2V?1s?1 at room temperature and 55 500 cm2V?1s?1 at 77 K in these samples with sheet carrier concentrations at 1 33 × 1012 cm?2 (room temperature) and 1.26 × 1012 cm?12 (77 K).     

不同插入层对抑制Mg掺杂p-GaN的记忆效应

研究了低温(LT) GaN和AlN不同插入层对抑制Mg掺杂p-GaN金属有机化学气相沉积外延中存在的记忆效应的影响,外延生长p-GaN缓冲层,制作具有该缓冲层的AlGaN/GaN高电子迁移率晶体管(HEMT),并对该器件进行电学测试.二次离子质谱仪测试表明p-GaN上10 nm厚的LT-GaN插入层相比于2 nm厚的AlN插入层能更好地抑制Mg扩散.霍尔测试表明,2 nm厚的AlN插入层的引入和GaN存在较大的晶格失配会引入位错,进而会降低AlGaN/GaNHEMT的电子迁移率以及增加其方块电阻;含有10 nm厚的LT-GaN插入层的p-GaN作为缓冲层的AlGaN/GaN HEMT,其方块电阻、电子迁移率以及二维电子气(2DEG)密度分别为334.9 Ω/口,1 923 cm2/(V·s)和9.68×1012 cm-2.器件具有很好的直流特性,其饱和电流为470 mA/mm,峰值跨导为57.7 mS/mm,电流开关比为3.13×109.     

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.     

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures

Sheet electron concentration at the heterointerface in Al0.48In0.52As/Ga0.47In0.53As modulation-doped structures has been calculated as a function of the spacer layer thickness, the doping concentration in Al0.48In0.52As and the lattice temperature. The calculated results were compared with those for Al0.3Ga0.7As/GaAs structures and also with the experimental data. It is shown that, compared with AlGaAs/GaAs about 1.5 times higher sheet electron concentration can be obtained in AlInAs/GaInAs at the same doping level, which is in good agreement with the experimental results.     

The influence of composition and unintentional doping on the two-dimensional electron gas density in AlGaN/GaN heterostructures

We have studied the influence of Al content, AlGaN layer thickness, and unintentional background doping by oxygen on the two-dimensional electron gas (2DEG) density in AlGaN/GaN heterostructures. Hall measurements were made on samples grown with molecular beam epitaxy. The 2DEG densities in the range 2–3×10¹³ cm^?2 were measured. A one-dimensional Schrödinger-Poisson model was used to describe the heterostructure. The calculations gave two-dimensional electron densities in accordance with measured values. The electron density is very sensitive to the Al concentration in the AlGaN layer, whereas the sensitivity to layer thickness is small. Our simulations also showed that the two-dimensional concentration increased 50% when the free-carrier concentration changed from 10¹⁵ cm^?3 to 10¹⁸ cm^?3. The relation between donor concentration and free-carrier concentration was found to agree when using oxygen ionization energy as a parameter.     

A new low-noise AlGaAs/GaAs 2DEG FET with a surface undoped layer

A high-performance N-AlGaAs/GaAs selectively doped two-dimensional electron gas (2DEG) FET with a surface undoped layer has been designed and demonstrated. Simple analysis based on the short-channel approximation revealed that an increase in a total layer thickness between a gate electrode and 2DEG at a hetero-interface results in a higher cutoff frequency and a lower noise figure than conventional 2DEG FET's. This is because the gate capacitance can be markedly reduced without a significant decrease in the transconductance owing to a parasitic source resistance. The surface undoped layer intentionally employed in this work can permit the total layer thickness to increase, i.e., the gate capacitance to reduce, without changes in the 2DEG density and in the source resistance. This structure also gives high gate breakdown voltage because of a small neutral region in n- (AlGa)As and a low surface electron field, which possibly yields excellent performance 2DEG FET's for practical use. Fabricated (AlGa)As/ GaAs 2DEG FET's exhibited noticeable room-temperature performances of 0.95-dB noise figure with 10.3-dB associated gain at 12- and 45-GHz cutoff frequency. These are the best data ever reported for 0.5-µm gate length FET's.     

量子点场效应单光子探测器二维电子气电子迁移率分析

设计了一种基于场效应晶体管的量子点场效应单光子探测器,利用二维弛豫时间的近似理论建立了二维电子气电子迁移率的散射模型,通过求解量子点场效应单光子探测器GaAs/AlxGa1-xAs二维电子气系统电子和声子相互作用的Hamiltonian函数,得到了不同温度、不同Al组分以及不同二维电子气电子面密度条件下晶格振动散射对探测器二维电子气电子迁移率的影响.仿真结果显示,提高二维电子气的电子面密度浓度和适当增大Al组分,并降低工作温度,有助于探测器获得更高的二维电子气电子迁移率.     

Electron mobility in two-dimensional electron gas in AIGaN/GaN heterostructures and in bulk GaN

We report on temperature dependencies of the electron mobility in the two-dimensional electron gas (2DEG) in AIGaN/GaN heterostructures and in doped bulk GaN. Calculations and experimental data show that the polar optical scattering and ionized impurity scattering are the two dominant scattering mechanisms in bulk GaN for temperatures between 77 and 500K. In the 2DEG in AIGaN/GaN heterostructures, the piezoelectric scattering also plays an important role. Even for doped GaN, with a significant concentration of ionized impurities, a large volume electron concentration in the 2DEG significantly enhances the electron mobility, and the mobility values close to 1700 cm²/Vs may be obtained in the GaN 2DEG at room temperature. The maximum measured Hall mobility at 80K is nearly 5000 cm²/Vs compared to approximately 1200 cm²/Vs in a bulk GaN layer. With a change in temperature from 300 to 80K, the 2DEG in our samples changes from nondegenerate and weakly degenerate to degenerate. Therefore, in order to interpret the experimental data, we propose a new interpolation formula for low field mobility limited by the ionized impurity scattering. This formula is valid for an arbitrary degree of the electron gas degeneracy. Based on our theory, we show that the mobility enhancement in the 2DEG is related to a much higher volume electron concentration in the 2DEG, and, hence, to a more effective screening.