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。     

二次退火对Al/Ti/n-GaN/Si欧姆接触的影响

采用热壁外延的方法在硅衬底上生长出n-GaN晶体,制成了Ti/Al双层电极的欧姆接触。通过对不同退火条件下的I-V特性曲线、X射线衍射及二次离子质谱分析,揭示了界面固相反应对该接触的影响,并提出了一种新的二次退火的方法。结果表明,经过二次退火后,Al、Ti、GaN发生了界面固相反应,其接触性能明显提高。     

快速热退火对Au/AuBe/Au与GaP结构的影响

采用金属有机化学气相沉积(MOCVD)制备了GaAs基A1GaInP发光二极管(LED),其中在p-GaP上制作Au/AuBe/Au接触电极,经不同温度快速热退火后,使用扫描电子显微镜(SEM)、X射线光电子能谱仪(XPS)和俄歇电子能谱仪(AES)对样品的欧姆接触的界面特性进行了分析和表征.使用光电测试仪对样品的电性能进行了测试.结果表明,随着退火温度的升高,各元素的扩散深度和强度增加,Au表面出现灰色片状聚合物,其主要成分为AuGa和BeO;在490～550℃时,金属层与GaP界面表层Au中含有Ga和Be元素,GaP中含有Au和Be元素;Ga元素扩散至Au层中,Au3Be相分解并形成β-AuGa,金属层物相结构转变成Au与3-AuGa两相的混合.在490～550℃时LED的正向电压保持不变.     

关于石墨烯上Ge/Au/Ni/Au欧姆接触的对比研究

Superior graphene-metal contacts can improve the performance of graphene devices. We report on an experimental demonstration of Ge/Au/Ni/Au-based ohmic contact on graphene. The transfer length method （TLM） is adopted to measure the resistivity of graphene-metal contacts. We designed a process flow, which can avoid residual photoresist at the interface of metal and graphene. Additionally, rapid thermal annealing （RTA） at different temperatures as a post-processing method is studied to improve graphene-metal contact. The results reveal that the contact resistivity of graphene and Ge/Au/Ni/Au can reach 10^-5 Ω· cm^2 after RTA, and that 350 ℃ is optimum annealing temperature for the contact of graphene-Ge/Au/Ni/Au. This paper provides guidance for fabrication and applications of graphene devices.     

n-GaN基Ti/Al/Ni/Au的欧姆接触高温特性

研究了在高温工作环境下Ti/Al/Ni/Au(15nm/220nm/40nm/50nm)四层复合金属层与n-GaN的欧姆接触的高温工作特性.退火后样品在500℃高温下工作仍能显示出良好的欧姆接触特性;接触电阻率随测量温度的增加而增大,且增加幅度与掺杂浓度有密切关系.掺杂浓度越高,其接触电阻率随测量温度的升高而增加越缓慢;重掺杂样品的Ti/Al/Ni/Au-n-GaN欧姆接触具有更佳的高温可靠性;当样品被施加500℃,1h的热应力后,其接触电阻率表现出不可恢复性增加.     

n-GaN基Ti/Al/Ni/Au的欧姆接触高温特性

研究了在高温工作环境下Ti/Al/Ni/Au(15nm/220nm/40nm/50nm)四层复合金属层与n-GaN的欧姆接触的高温工作特性.退火后样品在500℃高温下工作仍能显示出良好的欧姆接触特性;接触电阻率随测量温度的增加而增大,且增加幅度与掺杂浓度有密切关系.掺杂浓度越高,其接触电阻率随测量温度的升高而增加越缓慢;重掺杂样品的Ti/Al/Ni/Au-n-GaN欧姆接触具有更佳的高温可靠性;当样品被施加500℃,1h的热应力后,其接触电阻率表现出不可恢复性增加.     

Au/p-CdZnTe欧姆接触的研究

研究了在60℃下大气中退火不同时间对Au/p-CdZnTe(CZT)欧姆接触特性的影响.通过I-V测试发现,退火2 h时,Au/p-CZT能得到较好的欧姆接触特性.用SEM和XPS进一步分析发现,在2 h退火过程中,Au大量向CZT体表层扩散,作为受主杂质占据Cd位,对CZT体表层进行了p型重掺杂,形成了M-p -p型欧姆接触.Cd、Te在退火过程中几乎未向Au层扩散,Au在扩散过程中未与CZT中的元素形成任何化合物.同时,CZT侧面有27.01%的Te氧化成有钝化作用的TeO2.     

退火对Ni/3C-SiC欧姆接触的影响

采用溅射法在液相外延 3 C-Si C上制备 Ni电极 ,并利用圆形传输线法研究了退火温度对欧姆接触特性的影响 ,实验表明对于 Ni/n-Si C金半接触 ,经过 80 0～ 1 0 0 0°C高温退火 5分钟后 ,肖特基整流特性退化为欧姆接触 ,表现出良好的欧姆接触特性 ,且随退火温度的提高 ,接触电阻进一步下降 ,1 0 0 0°C退火后 ,可获得最低的接触电阻为 5 .0× 1 0 - 5Ω· cm2。     

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。     

欧姆接触金属退火对应力AlGaN/GaN异质结构中电子迁移率的影响

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.     

Effect of annealing temperature on Ti/Al/Ni/Au ohmic contacts on undoped AlN films

The Ti/Al/Ni/Au metals were deposited on undoped AlN films by electron beam evaporation. The influence of annealing temperature on the properties of contacts was investigated. When the annealing temperatures were between 800 and 950℃, the AlN-Ti/Al/Ni/Au contacts became ohmic contacts and the resistance decreased with the increase of annealing temperature. A lowest specific contacts resistance of 0.379 Ω·cm² was obtained for the sample annealed at 950℃. In this work, we confirmed that the formation mechanism of ohmic contacts on AlN was due to the formation of Al-Au, Au-Ti and Al-Ni alloys, and reduction of the specific contacts resistance could originate from the formation of Au₂Ti and AlAu₂ alloys. This result provided a possibility for the preparation of AlN-based high-frequency, high-power devices and deep ultraviolet devices.     

Au/Pt/AuGe/Ni中Pt扩散阻挡层对n-GaAs欧姆接触的影响

The multi-layer metals of Ni/Au Ge/Pt/Au with a Pt diffusion barrier layer of ohmic contact to n-GaAs were studied. The surface morphology and ohmic contact resistivity of multi-layer metals were characterized, with and without the Pt diffusion barrier layer for comparison. The SEM and EDS measurements show the Pt diffusion barrier layer can block the interdiffusion of atoms in multi-layer metals, and improve the surface morphology.The TLM results show that the samples with a Pt diffusion barrier layer have uniform ohmic contact resistance,indicating that the Pt diffusion barrier layer can increase the repetition and uniformity of ohmic contact to n-GaAs,and improve the thermal stability and reliability of GaAs-based devices.     

Microstructural and electrical investigation of Ni/Au ohmic contact on p-type GaN

Electrical properties of Ni/Au ohmic contacts on p-type GaN were interpreted with the change of microstructure observed under transmission electron microscopy. The contact resistivity was decreased from 1.3×10⁻² to 6.1×10⁻⁴ Ωcm² after annealing at 600°C. The reduction is due to the dissolution of Ga atoms into Au−Ni solid solution formed during annealing, via the generation of Ga vacancies. Thus, net concentration of holes increased below the contact, resulting in the reduction of contact resistivity. At 800°C, N atoms decomposed; reacted with Ni, and forming cubic Ni₄N. Consequently, N vacancies, acting as donors in GaN, were generated below the contact, leading to the increase of contact resistivity to 3.8×10⁻² Ωcm².     

p-GaN Ni/Au 电极退火后NiO的除去

The Ni/Au contact was treated with oxalic acid after annealing in 02 ambient, and its 1-V characteristic showed the property of contact has been obviously improved. An Auger electron spectroscopy （AES） depth profile of the contact as-annealed showed that the top layer was highly resistive NiO, while an X-ray photo-electron spectroscopy （XPS） of oxalic acid treated samples indicated that the NiO has been removed effectively. A scanning electron microscope （SEM） was used to observe the surface morphology of the contacts, and it was found that the lacunaris surface right after annealing became quite smooth with lots of small Au exposed areas after oxalic acid treatment. When the test probe or the subsequently deposited Ti/Au was directly in contact with these small Au areas, they worked as low resistive current paths and thus decrease the specific contact resistance.     

NiO removal of Ni/Au Ohmic contact to p-GaN after annealing

The Ni/Au contact was treated with oxalic acid after annealing in O2 ambient, and its I-V characteristic showed the property of contact has been obviously improved. An Auger electron spectroscopy (AES) depth pro-file of the contact as-annealed showed that the top layer was highly resistive NiO, while an X-ray photo-electron spectroscopy (XPS) of oxalic acid treated samples indicated that the NiO has been removed effectively. A scanning electron microscope (SEM) was used to observe the surface morphology of the contacts, and it was found that the lacunaris surface right after annealing became quite smooth with lots of small Au exposed areas after oxalic acid treatment. When the test probe or the subsequently deposited Ti/Au was directly in contact with these small Au areas, they worked as low resistive current paths and thus decrease the specific contact resistance.     

The microstructure characterization of ultrasmall eutectic Bi-Sn solder bumps on Au/Cu/Ti and Au/Ni/Ti under-bump metallization

The microstructure of the ultrasmall eutectic Bi-Sn solder bumps on Au/Cu/Ti and Au/Ni/Ti under-bump metallizations (UBMs) was investigated as a function of cooling rate. The ultrasmall eutectic Bi-Sn solder bump, about 50 μm in diameter, was fabricated by using the lift-off method and reflowed at various cooling rates using the rapid thermal annealing system. The microstructure of the solder bump was observed using a backscattered electron (BSE) image and the intermetallic compound was identified using energy dispersive spectroscopy (EDS) and an x-ray diffractometer (XRD). The Bi facet was found at the surface of the ultrasmall Bi-Sn solder bumps on the Au/Cu/Ti UBM in almost all specimens, and the interior microstructure of the bumps was changed with the solidification rate. The faceted and polygonal intermetallic compound was found in the case of the Bi-Sn solder bump on the Au (0.1 μm)/Ni/Ti UBM, and it was confirmed to be the (Au_1−x−yBi_xNi_y)Sn₂ phase by XRD. The intermetallic compounds grown form the Au (0.1 μm)/Ni/Ti UBM interface, and they interrupted the growth of Bi and Sn phases throughout the solder bump. The ultrasmall eutectic Bi-Sn solder bumps on the Au (0.025 μm)/Ni/Ti UBM showed similar microstructures to those on the Au/Cu/Ti UBM.     

退火工艺对La-Nb共掺杂Bi_4Ti_3O_(12)薄膜结构的影响

采用sol-gel法制备了Si基Bi3.25La0.75Ti2.94Nb0.06O12.03(BLTN)铁电薄膜,研究了退火温度、升温速率和退火时间对BLTN薄膜微观结构的影响。结果表明:制备的BLTN薄膜具有单一的钙钛矿结构,且为随机取向,表面平整致密;退火温度由550℃升高到750℃时,薄膜的衍射峰强度增强,晶粒尺寸由65 nm增大到110 nm;退火升温速率由10℃/min提高为20℃/min时,薄膜的晶化程度降低;退火时间对薄膜的晶相结构影响不大,但时间超过30 min会造成薄膜表面孔洞增多、致密性下降。     

退火温度对NdFeO_3微结构及酒敏性能的影响

采用sol-gel法制备了具有单一斜方钙钛矿结构的NdFeO3样品,研究了退火温度对NdFeO3样品的晶格常数、微结构、电性能及酒敏特性的影响。结果表明:随着退火温度的提高,样品的晶胞体积减小,晶粒度变大,利用该样品制成的气敏元件的电导也随之增大。800℃退火的样品显示出最佳酒敏特性,元件对体积分数为5×10–4的乙醇的最大灵敏度高达151.69,不同退火温度的样品均显示出较好的低温(90℃左右)工作特性。