Fabrication of Ti ohmic contact to n-type 6H-SiC without high-temperature annealing

The effect of surface morphology of 6H-SiC substrate on the ohmic contact properties of Ti/6H-SiC structure is studied. The H-terminated surface on Si-face 6H-SiC is obtained by both dipping SiC into HF acid solution for 15 s and thermal heating SiC in hydrogen atmosphere at 1100 C for 10 min, while the H-terminated surface on C-face 6H-SiC could be obtained only by the latter method. Ti is deposited on Si-face and C-face SiC substrates with H-terminated surfaces and ohmic contact is obtained without high-temperature annealing.     

氢氟酸刻蚀对Ni/6H-SiC接触性质的作用

采用浓度为10%的氢氟酸（HF）刻蚀6H-SiC单晶片,研究了HF刻蚀时间对Ni/6H-SiC接触性质的影响．经24?h刻蚀的SiC基片在溅射Ni层后,其接触表现良好线性的电流-电压（I-V）曲线．低于这个腐蚀时间的接触具有明显的势垒,但在大于1000℃快速退火后,也得到了良好线性的I-V曲线．X射线衍射（XRD）和俄歇能谱（AES）深度元素分析表明Ni₂Si和C是快速退火后的主要产物．XRD和低能反射电子能量损失谱表明表层的C 关键词： 欧姆接触 SiC 富碳层 互扩散     

Ti--Al based ohmic contacts to n-type 6H-SiC with P+ ion implantation

The Ti--Al ohmic contact to n-type 6H-SiC has been fabricated. An array of TLM (transfer length method) test patterns with Au/Ti/Al/Ti/SiC structure is formed on N-wells created by P⁺ ion implantation into Si-faced p-type 6H-SiC epilayer. The specific contact resistance \rho _c as low as 8.64×10^-6\Omega\cdot cm² is achieved after annealing in N₂ at 900℃ for 5\,min. The sheet resistance R_sh of the implanted layers is 975\Omega/\sqcap\!\!\!\!\sqcup. X-ray diffraction (XRD) analysis shows the formation of Ti_-3SiC₂ at the metal/n-SiC interface after thermal annealing, which is responsible for the low resistance contact.     

硅衬底GaN基LED N极性n型欧姆接触研究

在Si衬底GaN基垂直结构LED的N极性n型面上,利用电子束蒸发的方法制作了Ti/Al电极,通过了I-V曲线研究了有无AlN缓冲层对这种芯片欧姆接触的影响.结果显示,去除AlN缓冲层后的N极性n型面与Ti/Al电极在500到600 ℃范围内退火才能形成欧姆接触.而保留AlN缓冲层的N极性n型面与Ti/Al电极未退火时就表现为较好的欧姆接触,比接触电阻率为2×10^-5 Ω·cm²,即使退火温度升高至600 ℃,也始终保持着欧姆接触特性.因此,AlN缓冲层的存在是Si衬底GaN基垂直结构LED获得高热稳定性n型欧姆接触的关键. 关键词： 硅衬底 N极性 AlN缓冲层 欧姆接触     

Si(100)表面Se薄膜生长及其在Ti/Si欧姆接触中的应用

本文采用分子束外延(MBE)系统在Si(100)表面淀积Se薄膜. 通过控制衬底和固态Se束源炉的温度,实现了Se材料在Si(100)表面上的自限制超薄薄膜生长;在Se超薄层钝化的Si(100)表面上制备的Ti金属电极具有低的欧姆接触电阻特性,且热稳定性温度提升至400 ℃. 关键词： 硒 钝化 欧姆接触 热稳定性     

不同退火方式对Ni/SiC接触界面性质的影响

采用快速热退火(rapid thermal annealing, RTA)法和脉冲激光辐照退火(laser spark annealing, LSA)法, 在n型4H-SiC的Si面制备出Ni电极欧姆接触. 经传输线法测得RTA样品与LSA样品的比接触电阻分别为5.2×10^-4 Ω·cm², 1.8× 10^-4 Ω·cm². 使用扫描电子显微镜、原子力显微镜、透射电子显微镜、拉曼光谱等表征手段, 比较了两种退火方式对电极表面形貌、电极/衬底截面形貌和元素成分分布、SiC衬底近表层碳团簇微结构的影响. 结果表明, 相比于RTA, LSA法制备出的欧姆接触在电极表面形貌、界面形貌、电极层组分均匀性等方面都具有明显优势, 有望使LSA成为一种非常有潜力的制备欧姆接触的退火处理方法.     

基于铟锡氧化物/Ti复合电极的高亮度碳纳米管场致发射冷阴极

通过制作亲碳性铟锡氧化物(ITO)/Ti复合电极,改善移植型碳纳米管(CNT)冷阴极的导电电极与CNT膜层之间附着性能,从而消除CNT与电极间的界面势垒和非欧姆接触对CNT阴极场发射均匀性和稳定性的影响.采用磁控溅射技术和丝网印刷工艺制作了ITO/Ti基CNT阴极.用X射线衍射仪和场致发射扫描电子显微镜表征CNT阴极结构,结果显示热处理后的ITO/Ti基CNT阴极中可能有TiC相生成,从而使得导电电极与CNT形成有中间物的强作用体系.该体系降低甚至消除电极与CNT之间的界面势垒,增加了CNT与电极间形成欧姆接触的概率.用四探针技术分析电阻率,结果表明ITO/Ti复合电极具有电阻并联效果,CNT阴极导电性能提高.场致发射特性测试表明ITO/Ti基CNT阴极的场致发射电流达到384μA/cm2,较普通ITO基CNT阴极的场致发射电流有显著提高,能够激发测试阳极发出均匀、稳定的高亮度荧光.制作ITO/Ti复合电极是实现场致发射稳定、均匀的低功耗CNT阴极的有效途径.     

Solid State Reaction of Ruthenium with 6H-SiC Under Vacuum Annealing and the Impact on the Electrical Performance of its Schottky Contact for High Temperature Operating SiC-Based Diodes

Thin films and Schottky diodes dots of ruthenium (Ru) on bulk-grown n-type-6-hexagonal-silicon carbide (6H-SiC) were annealed isochronally in a vacuum furnace at temperatures ranging from 500–1,000 °C. Rutherford backscattering spectroscopy analysis of the thin films showed formation of ruthenium silicide (Ru₂Si₃) at 800 °C, while diffusion of Ru into 6H-SiC commenced at 800 °C. Raman analysis of the thin films annealed at 1,000 °C showed clear D and G carbon peaks which was evidence of formation of graphite. At this annealing temperature, the Schottky contact was observed to convert to an ohmic contact, as evidenced by the linearity of current–voltage characteristic, thereby, rendering the diode unusable. The transformation from Schottky contact to ohmic contact is attributed to graphite formation at the interface.     

Structural characterization of nickel-titanium film on silicon carbide

The presented work describes behavior of contact structures of Ni/Ti type on 6H-SiC n-type. The best contact resistivity obtained is 3.3 × 10⁻⁴ Ω cm². The structure showed excellent thermal stability, it was stable after being tested for 10 h at 900 °C. XRD analysis after annealing at 960 °C revealed orthorhombic Ni₂Si as the dominate phase.     

Mechanism of atomic-scale passivation and flattening of semiconductor surfaces by wet-chemical preparations

Atomic arrangements of Si(001), Si(110) and 4H-SiC(0001) surfaces after wet-chemical preparations are investigated with scanning tunneling microscopy. Their passivated structures as well as the surface formation mechanisms in aqueous solutions are discussed. On both Si(001) and Si(110) surfaces, simple 1 × 1 phases terminated by H atoms are clearly resolved after dilute HF dipping. Subsequent etching with water produces the surfaces with 'near-atomic' smoothness. The mechanisms of atomic-scale preferential etching in water are described in detail together with first-principles calculations. Furthermore, 4H-SiC(0001), which is a hard material and where it is difficult to control the surface structure by solutions, is flattened on the atomic scale with Pt as a catalyst in HF solution. After a mechanism is proposed based on electroless oxidation, the flattened surface mainly composed of a 1 × 1 phase is analyzed. The obtained results will be helpful from various scientific and technological viewpoints.     

Structural and electrical properties of Au/Pt/Ti ohmic contacts to degenerated doped n-GaAs

The ohmic contact characteristics of Au/Pt/Ti on degenerated doped n-GaAs were evaluated. Structural and electrical properties were studied by means of X-ray diffraction (XRD), Auger Energy Spectrum (AES) and a HP4145B parameter analyzer. The structural analysis revealed a TiAs phase in the interface between metal multilayer and GaAs at higher annealing temperatures. Electrical measurement showed a minimum ohmic contact resistance of 3×10^-4 Ω cm². The dominant current mechanism was found to be thermionic emission with a barrier height of Φ_b, of 0.09 V by comparing the experimental data with different theoretical models. Received: 14 December 2001 / Accepted: 4 April 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +86-21/6226-4397, E-mail: zhoujian999@163.net     

The fabrication of nickel silicide ohmic contacts to n-type 6H-silicon carbide

This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi硅化镍;欧姆触点;n型碳化硅;制造;能带;带隙Project supported by the National Basic Research Program of China (Grant No~2002CB311904), the National Defense Basic Research Program of China (Grant No~51327010101) and the National Natural Science Foundation of China (Grant No~60376001).2006-09-192006-10-30This paper reports that the nickel silicide ohmic contacts to n-type 6H-SiC have been fabricated. Transfer length method test patterns with NiSi/SiC and NiSi2/SiC structure axe formed on N-wells created by N^＋ ion implantation into Si-faced p-type 6H-SiC epilayer respectively. NiSi and NiSi2 films are prepared by annealing the Ni and Si films separately deposited. A two-step annealing technology is performed for decreasing of oxidation problems occurred during high temperature processes. The specific contact resistance Pc of NiSi contact to n-type 6H-SiC as low as 1.78× 10^-6Ωcm^2 is achieved after a two-step annealing at 350 ℃for 20 min and 950℃ for 3 min in N2. And 3.84×10-6Ωcm^2 for NiSi2 contact is achieved. The result for sheet resistance Rsh of the N＋ implanted layers is about 1210Ω/□. X-ray diffraction analysis shows the formation of nickel silicide phases at the metal/n-SiC interface after thermal annealing. The surfaces of the nickel silicide after thermal annealing are analysed by scanning electron microscope.     

Study of electronic structures for Fe thin films deposited on Si- and C-faces of 4H-SiC substrates by soft X-ray emission spectroscopy

Silicon carbide (SiC) is a candidate material for electronic devices to operate upon crucial environment. Electronic states of silicides and/or carbide/graphite formed in metal/SiC contact system are fundamentally important from the viewpoint of device performance.We study interface electronic structure of iron thin film deposited on silicon (Si)- and carbon (C)-face of 4H-SiC(0 0 0 1) by using a soft X-ray emission spectroscopy (SXES). For specimens of Fe (50 nm)/4H-SiC (substrate) contact systems annealed at 700 and 900 °C, the Si L_2,3 emission spectra indicate different shapes and peak energies from the substrate depending on thermal-treated temperature. The product of materials such as silicides is suggested. Further, from comparison of Si L_2,3 emission spectra between Si- and C-face for the same annealing temperature at 700 °C, it is concluded that the similar silicides and/or ternary materials are formed on the two surfaces. However for those of 900 °C, the film on substrate is composed of the different silicide and/or ternary materials.     

Titanium-modified Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> with a synergistic effect of surface modifying,bulk doping,and size reducing

In this work, a one-step solid-phase sintering process via TiO₂ and Li₂CO₃ under an argon atmosphere, with ultra-fine titanium powder as the modifying agent, was used to prepare a nano-sized Li₄Ti₅O₁₂/Ti composite (denoted as LTO–Ti) at 800 °C. The introduction of ultra-fine metal titanium powder played an important role. First, X-ray photoelectron spectroscopy demonstrates that Ti⁴⁺ was partially changed into Ti³⁺, through the reduction of the ultra-fine metal titanium powder. Second, X-ray diffraction revealed that the ultra-fine metal titanium powder did not react with the bulk structure of Li₄Ti₅O₁₂, while some pure titanium peaks could be seen. Additionally, the size of LTO–Ti particles could be significantly reduced from micro-scale to nano-scale. The structure and morphology of LTO–Ti were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Electrochemical tests showed a charge/discharge current of 0.5, 1, 5, and 10 C; the discharge capacity of the LTO–Ti electrode was 170, 161, 140, and 111 mAh g^?1. It is believed that the designed LTO–Ti composite makes full use of both components, thus offering a large contact area between the electrolyte and electrode, high electrical conductivity, and lithium-ion diffusion coefficient during electrochemical processes. Furthermore, ultra-fine titanium powder, as the modifying agent, is amenable to large-scale production.     

Influence of deep defects on electrical properties of Ni/4H-SiC Schottky diode

In this paper, we investigate the influence of deep level defects on the electrical properties of Ni/4H-SiC Schottky diodes by analyzing device current-voltage(I-V) characteristics and deep-level transient spectra(DLTS). Two Schottky barrier heights(SBHs) with different temperature dependences are found in Ni/4 H-SiC Schottky diode above room temperature. DLTS measurements further reveal that two kinds of defects Z_(1/2) and Ti(c)~a are located near the interface between Ni and SiC with the energy levels of E_C-0.67 eV and E_C-0.16 eV respectively. The latter one as the ionized titanium acceptor residing at cubic Si lattice site is thought to be responsible for the low SBH in the localized region of the diode, and therefore inducing the high reverse leakage current of the diode. The experimental results indicate that the Ti(c)~a defect has a strong influence on the electrical and thermal properties of the 4 H-SiC Schottky diode.     

Thickness dependence on thermal stability of sputtered Ag nanolayer on Ti/Si(1 0 0)

Thermal stability of Ag layer on Ti coated Si substrate for different thicknesses of the Ag layer have been studied. To do this, after sputter-deposition of a 10 nm Ti buffer layer on the Si(1 0 0) substrate, an Ag layer with different thicknesses (150-5 nm) was sputtered on the buffer layer. Post annealing process of the samples was performed in an N₂ ambient at a flow rate of 200 ml/min in a temperature range from 500 to 700 °C for 30 min. The electrical property of the heat-treated multilayer with the different thicknesses of Ag layer was examined by four-point-probe sheet resistance measurement at the room temperature. Phase formation and crystallographic orientation of the silver layers were studied by θ-2θ X-ray diffraction analysis. The surface topography and morphology of the heat-treated films were determined by atomic force microscopy, and also, scanning electron microscopy. Four-point- probe electrical measurement showed no considerable variation of sheet resistance by reducing the thickness of the annealed Ag films down to 25 nm. Surface roughness of the Ag films with (1 1 1) preferred crystallographic orientation was much smaller than the film thickness, which is a necessary condition for nanometric contact layers. Therefore, we have shown that the Ag layers with suitable nano-thicknesses sputtered on 10 nm Ti buffer layer were thermally stable up to 700 °C.     

在Si(111)上用有机溶胶凝胶甩膜热解法制备(0001)定向的6H-SiC薄膜

在Si(111)衬底上用聚苯乙烯溶胶凝胶甩膜并经950℃真空(10^-3Pa)热解处理法,制备出晶态SiC薄膜.用FTIR,XRD,TEM,RamanXPS等方法研究了SiC薄膜的晶体结构、微结构、组成以及各元素的化学态等性质.结果表明制得的是沿(0001)高度择优取向的晶态6H-SiC薄膜.膜中SiC晶粒沿c轴柱状生长,其最大尺寸约150nm,膜厚约为0.3μm,SiC中的Si/C比约为1.表层有少许污染C(CH和CO)和少量O(Si₂O₃,CO态氧和吸附氧).从对比实验可知,在热解时将甩膜的Si片与另一空白Si片面面相贴可明显增加SiC的生成量. 关键词： 碳化硅 薄膜 溶胶凝胶     

Self-aligned-gate AlGaN/GaN heterostructure field-effect transistor with titanium nitride gate

Self-aligned-gate heterostructure field-effect transistor(HFET) is fabricated using a wet-etching method.Titanium nitride(TiN) is one kind of thermal stable material which can be used as the gate electrode.A Ti/Au cap layer is fixed on the gate and acts as an etching mask.Then the T-shaped gate is automatically formed through over-etching the TiN layer in 30% H_2O_2 solution at 95 ℃.After treating the ohmic region with an inductively coupled plasma(ICP) method,an Al layer is sputtered as an ohmic electrode.The ohmic contact resistance is approximately 0.3 Ω·mm after annealing at a low-temperature of 575 ℃ in N_2 ambient for 1 min.The TiN gate leakage current is only 10~(-8) A after the low-temperature ohmic process.The access region length of the self-aligned-gate(SAG) HFET was reduced from 2 μm to 0.3 μm compared with that of the gate-first HFET.The output current density and transconductance of the device which has the same gate length and width are also increased.     

Plasma-assisted surface treatment for low-temperature annealed ohmic contact on AlGaN/GaN heterostructure field-effect transistors

In this study, a low-temperature annealed ohmic contact process was proposed on Al Ga N/Ga N heterostructure field effect transistors(HFETs) with the assistance of inductively coupled plasma(ICP) surface treatment. The effect of ICP treatment process on the 2DEG channel as well as the formation mechanism of the low annealing temperature ohmic contact was investigated. An appropriate residual Al Ga N thickness and a plasma-induced damage are considered to contribute to the low-temperature annealed ohmic contact. By using a single Al layer to replace the conventional Ti/Al stacks, ohmic contact with a contact resistance of 0.35 ?·mm was obtained when annealed at 575?C for 3 min. Good ohmic contact was also obtained by annealing at 500?C for 20 min.