二次退火对Au/Ni/Au/Ni/p-AlGaN欧姆接触组织结构的影响

在蓝宝石衬底上,利用金属-有机物化学气相沉 积(MOCVD)方法制备p-i-n结构AlGaN基体,采 用常规工艺制作台面型紫外探测器。电子束蒸发蒸镀Ni/Au/Ni/Au(20nm/20 nm)结构制备 p 电极。经空气中550℃/3min一次退火和N₂气氛中750℃/30s二次退火后得到欧姆接触。利用高分 辨透射电镜(HRTEM)和能谱(EDS)研究不同退火条件下p 电极接触的组织结构演变。结果 表明:一 次退火p电极金属层出现明显扩散,但仍维持初始的分层状态,金属/半导体接触界面产生 厚约4nm 的非晶层;二次退火后,金属电极分层现象和界面非晶层消失。金/半界面结构表现为半共 格关系,界面结 构有序性提高。Ni向外扩散,Au向内扩散,Ga扩散至金属电极,造成界面附近金属层富 集Au、Ga元素,导致p电极欧姆接触的形成。     

一种在砷化镓上形成欧姆接触的新型六层金属系统

研究了在砷化镓上欧姆接触形成机理,并提出了一种新型的欧姆接触六层金属系统(Ni/Ge/Au/Ge/Ni/Au).在n型GaAs样品上实验了在380～460℃合金温度和50～120 s合金时间下形成欧姆接触,在400℃、60 s下典型的欧姆接触值为2.1x10-7Ω·cm2,同时合金后表面形貌光滑、平整.     

合金条件对Al/n~+-Ge欧姆接触的影响

Ge比Si具有更高的电子和空穴迁移率,且Ge材料可以应用于1.3～1.5μm近红外波段,因此Ge成为制备微电子和光电子器件的主要材料。然而由于Ge的费密能级钉扎效应以及难以获得高浓度的磷(P)原位掺杂,使得n-Ge的欧姆接触成为一个难题。采用P+离子注入获得高掺杂浓度的n-Ge材料,掺杂浓度为1.5×1019cm-3;依据圆形传输线模型(CTLM)制备了一系列Al/n+-Ge样品,研究了不同退火温度和退火方式对其接触特性的影响。实验结果表明,Al/n+-Ge样品通过400℃快速热退火(RTA)30 s表现出欧姆接触特性,并且接触电阻率ρc最低,为1.3×10-5Ω·cm2。     

InAs/InP量子点激光器中欧姆接触合金层特性研究

合金层与InAs/InP量子点激光器的接触电阻对激光 器的性能有很大影响,而接触电阻的 大小与合金材料、退火温度和退火时间有关。本文采用Au/Ni/Au/Ge做InAs/InP量子点激光 器的欧姆接触合金层,通过改变退 火温度和退火时间调节量子点激光器中接触电阻的阻值。实验发现,退火时间对接触电阻的 改变不 大,但是提高退火温度却能极大地降低接触电阻的阻值。实验获得了Au/Ni/Au/Ge 合金层与InAs/InP量子点激光器最佳欧姆接触条件,通过矩阵传输法测得相应接触电阻率为 1.34×10－6 Ω·cm²。在此条件下,制备激射中心波长为 1.577μm的多模量子点 激光器,室温下单面最大输出功率达到和超过39mW。     

Ge／Pt／Au,Ge／Au／Ni／Au—n型GaAs欧姆接触的对比研究

对用快速热合金方法（RTP）形成Ge/Pt/Au,Ge/Au/Ni/Au-n型GaAs欧姆接触进行了对比研究。实验结果表明，在合金形貌和欧姆接触特性兼顾的情况下，Ge/Pt/Au和Ge/Au/Ni/Au有不同的“温度－时间”窗口的接触电阻率。合金后，Auger能谱分析表明，Ge/Au/Ni/Au金属系统扩散进GaAs体内的净施主Ge浓度较高，因而接触电阻率较低。两种欧姆接触金属系统经高温存贮一定时间后，发现其接触电阻率都有所降低。     

AlGaN紫外探测器p电极的Ni/Au/Ni/Au欧姆接触结构研究

研究了AlGaN半导体p电极的Ni/Au/Ni/Au接触结构的性能和组织结构。退火 前,p电极接触具有明显的整流特性。经空气中550℃/3 min一 次退火和N2气氛中750℃/30 s二 次退火后,电极呈现出了良好的欧姆接触。采用扫描电镜(Scanning Electron Microscope, SEM)、透射 电镜(Transmission Electron Microscope, TEM)、能量分散谱仪(Energy Dispersive Spectrometer, EDS)和X射 线光电子能谱(X-ray Photoelectron Spectroscopy, XPS)观察了电极退火后金--半界面微结构的演化过程。结果表明,完全退火后的p电极 界面及金属层出现了明显的互扩散和界面反应现象;金--半界面上形成了存在良好共格/半共格关系的外延结 构。初始沉积的金属电极分层现象消失,形成了单一的电极结构。Ni向外扩散并与O发生反应,Au扩散至p-GaN 表面。在金-半接触界面上,Ga扩散至金属电极,造成界面附近的金属层中富集Au和Ga元素;Au和Ni明显扩散 至半导体表层,在金-半界面附近形成了Au、Ga和Ni富集现象。这些现象应该对于降低势垒高度和形成欧姆接触具有重要作 用。     

低掺杂浓度n型GaAs欧姆接触的研究

利用传输线方法（TLM）重点研究了低掺杂浓度（2×1017at/cm3）n型GaAs接触层的欧姆接触,通过改变AuGe/Ni的厚度比、合金化的温度和时间等参数,获得了最优化的制备条件：AuGe/Ni/Au的厚度为50nm/25nm/100 nm,退火温度为400 ℃,退火时间为120s时,欧姆接触电阻率为最低3.52×10-4Ωcm-2,这一结果为量子阱结构太赫兹探测器芯片的制备奠定了基础。     

Ag/Au与n-ZnO的欧姆接触特性的研究

为了更好实现ZnO材料在光电器件方面的应用,研究了Ag/Au和n-ZnO薄膜的欧姆接触。通过半导体特性分析系统测出欧姆接触的I-V特性曲线和采用挖补圆盘法测试了欧姆接触的接触电阻率,研究了退火温度对接触特性的影响。利用俄歇电子能谱(AES)研究了欧姆接触的微观结构,比较了不同的金属电极的反射特性。结果表明,Ag(50nm)/Au(100nm)和n-ZnO薄膜的欧姆接触在退火温度为500℃时最好,欧姆接触电阻率仅为5.2×10-4Ω·cm-2,且其反射特性比其它金属电极好。     

Ni/Au与p-GaN的比接触电阻率测量

通过采用环形传输线方法(CILM),电流-电压(I-V)曲线、表面形貌等方法,研究不同的Ni/Au厚度比和空气气氛下合金退火温度对p型氮化镓欧姆接触特性造成的影响。根据Ni/Au与p型氮化镓欧姆接触的形成机制,采用合适的Ni/Au厚度比及退火温度,得到比接触电阻率(ρc)为1.09×10-5Ω.cm2的Ni/Au-p-GaN电极,并分析了Ni在退火过程中对形成良好的欧姆接触中所起到的作用。     

Ni层厚度对p-GaN/Ni/Au欧姆接触特性的影响

对p-GaN/Ni/Au欧姆接触特性与Ni金属层厚度之间的相关性进行了对比实验研究,利用XRD衍射结果与表面金相显微分析手段对Ni/Au双层金属电极在合金退火过程中的行为特性进行了细致探讨。分析结果表明:在Ni/Au电极结构中,由双层互扩散机制与NiO氧化反应机理决定,Ni层与Au层之间的厚度比率对p型GaN欧姆接触特性的优劣有重要影响,在Ni、Au层厚度相当时可获得最佳的p型欧姆接触。     

新型双区阴极结构体效应二极管

常规的GaAs体效应二极管的阴极结构多采用欧姆阴极,在毫米波频段(W 波段),器件的转换效率小于1%.介绍了一种新型的双区阴极结构在W 波段体效应二极管中的实现,并研制出了样品器件.采用此种结构,可以显著提高毫米波器件的输出功率和转换效率.     

Ideal ohmic contacts to InP

A new method of producing ohmic contacts to semiconducting n-type InP by the use of a slow alloying cycle with a P overpressure has resulted in improved contact fabrication. Gunn devices were produced with these contacts for the anode and cathode and their microwave characteristics were measured.     

All-refractory GaAs FET using amorphous TiWSixsource/drain metallization and graded-InxGa1-xAslayers

We report on the fabrication of an all-refractory GaAs field-effect transistor having non-alloyed source and drain ohmic contacts and a TiW/Au refractory gate metallization. The ohmic contacts consist of amorphous TiWSi_x metallization and intervening graded InGaAs layers grown by low pressure organometallic vapor phase epitaxy (LPOMVPE). The amorphous TiWSi_x, is formed using alternating layers of TiW(10 Å) and Si(1.5 Å) deposited by an RF magnetron sputtering technique. The resulting all-refractory FET devices exhibited excellent dc transistor characteristics with measured transconductance of 140 mS/mm. The dc performance of these devices was comparable to conventional devices with AuGe/Ni/Au contacts fabricated using similar material structures     

Negative conductance in semiconductors

Until recently, investigators have been frustrated in their attempts at applying microwave and millimeter-wave frequencies to semiconductor devices. During the last few years, the discovery of avalanche transit-time and Gunn effects in bulk semiconductors has been met with overwhelming enthusiasm. The successful fabrication of models presently utilizing these negative-conductance phenomena has given these high-frequency devices an optimistic outlook for the future.     

GaAs Integrated Microwave Circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits.The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (> 10 /sup 6/ ohm cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated circuits thus allows for improved microwave performance from the devices since parasitics are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94GHz) receiving front end.The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10 /sup 18/ -10 /sup 15/ -10 /sup 18/ cm /sup -3/.The Schottky diodes consist of two deposits with concentrations of 10 /sup 18/ and 10 /sup 17/ cm /sup -3/.The Schottky contact is formed by evaporating Mo-Au onto the 10 /sup 17/ cm /sup -3/ deposits; all ohmic contacts are on the surface and are alloyed to the N+ regions.     

GaAs integrated microwave circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits. The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (>10⁶ohm.cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated-circuits thus allows for improved microwave pedormance from the devices since parasitics are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94 GHz) receiving front end. The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10¹⁸-10¹⁵-10¹⁸cm^-3. The Schottky diodes consist of two deposits with concentrations of 10¹⁸and 10¹⁷cm^-3. The Schottky contact is formed by evaporating Mo-Au onto the 10¹⁷cm^-3deposits; all ohmic contacts are on the surface and are alloyed to the N⁺regions.     

GaAs Integrated Microwave Circuits

GaAs has many desirable features that make it most useful for microwave and millimeter-wave integrated circuits. The process of selective epitaxial depositions of high purity single-crystal GaAs with various doping concentrations into semi-insulating GaAs substrates has been developed. These high-resistivity substrates (>10/sup 6/ ohm /spl dot/ cm) provide the electrical isolation between devices, eliminating the difficulties and deficiencies normally encountered in trying to obtain isolation with dielectrics, back-etching, p-n junctions, etc. This monolithic approach to integrated circuits thus allows for improved microwave performance from the devices since parasitic are reduced to a minimum. Planar Gunn oscillators and Schottky barrier diodes have been fabricated for use in a completely monolithic integrated millimeter wave (94 GHz) receiving front end. The Gunn oscillators are made in a sandwich-type structure of three selective deposits whose carrier concentrations are approximately 10/sup 18/ - 10/sup/15/ - 10/sup 18/ cm/sup -3/. The Schottky diodes consist of two deposits with concentrations of 10/sup 18/ and 10/sup 17/ cm /sup -3/. The Schottky contact is formed by evaporating Mo-Au onto the 10/sup 17/cm/sup -3/ deposits; all ohmic contacts are on the surface and are alloyed to the N/sup +/ regions.     

Simplified ohmic and Schottky contact formation for field effecttransistors using the single layer integrated metal field effecttransistor (SLIMFET) process

A new III-V semiconductor device fabrication process for GaAs-based field effect transistors (FET) is presented which uses a single lithographic process and metal deposition step to form both the ohmic drain/source contacts and the Schottky gate contact concurrently. This single layer integrated metal FET (SLIMFET) process simplifies the fabrication process by eliminating an additional lithographic step for gate definition, a separate gate metallization step, and thermal annealing for ohmic contact formation. The SLIMFET process requires a FET structure which incorporates a compositionally graded In_xGa_1-xAs cap layer to form low resistance, nonalloyed ohmic contacts using standard Schottky metals. The SLIMFET process also uses a Si₃N₄ mask to provide selective removal of the InGaAs ohmic layers from the gate region prior to metallization without requiring an additional lithographic step. GaAs MESFET devices were fabricated using this new SLIMFET process which achieved DC and RF performance comparable to GaAs MESFET's fabricated by conventional methods     

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.     

A Planar Gunn Diode Operating Above 100 GHz

We show the experimental realization of a 108-GHz planar Gunn diode structure fabricated in GaAs/AlGaAs. There is a considerable interest in such devices since they lend themselves to integration into millimeter-wave and terahertz integrated circuits. The material used was grown by molecular beam epitaxy, and devices were made using electron beam lithography. Since the frequency of oscillation is defined by the lithographically controlled anode-cathode distance, the technology shows great promise in fabricating single chip terahertz sources.