氧化Au/Ni/p-GaN欧姆接触形成的机理

用卢瑟福背散射（RBS）和同步辐射X射线衍射（XRD）研究了p-GaN上的Ni/Au电极在空气下不同温度合金后的微结构的演化，并揭示这种接触结构的欧姆接触形成机制．研究不同温度下比接触电阻(ρc)的变化，发现从450℃开始Au扩散到GaN的表面在p-GaN上形成外延结构以及O向电极内部扩散反应生成NiO对降低ρc起到了关键的作用．在500℃时，Au的外延结构进一步改善，O进一步向样品内部扩散生成NiO,ρc也达到了最低值．但当合金温度升高到600℃时，金属-半导体界面NiO的大部分或全部向外扩散，从而脱离与p-GaN的接触，使ρc显著升高．     

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。     

低温退火制备Ti/4H-SiC欧姆接触

实现SiC器件欧姆接触常规工艺需要800～1200℃的高温退火.研究了n型4H-SiC低温制备Ti欧姆电极的工艺及其基本电学特性.通过氢等离子体处理4H-SiC的表面,沉积Ti后可直接形成欧姆接触,室温下比接触电阻率ρc为2.25×10-3 Ω·m2(ρc由圆形传输线模型CTLM测得),随着合金温度的升高,其欧姆特性逐渐增强,400℃合金后获得最低的比接触电阻率ρc为2.07×10-4 Ω·m2.采用X射线衍射(XRD)确定金属/n-SiC界面反应时形成的相,以分析电学性质与微观结构间的联系.最后讨论了低温欧姆接触的形成机制.     

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。     

Si衬底LED薄膜芯片Ni/Ag反射镜保护技术

Ag基反射镜提高了薄膜型LED芯片的出光效率,但其易受破坏,通常选择抗腐蚀金属作为其保护材料,同时需要研究保护金属与p-GaN的接触性能,避免在p-GaN上同时形成两种欧姆接触引入的电流分流效应。通过传输线的方法研究了Pt,Cr,Ni/Ag与p-GaN的接触行为(在不同的合金条件),讨论了Cr和Pt作为保护材料的可行性。结果发现,N2中500℃合金后,NiAg/p-GaN的比接触电阻率(ρc)达到最低,ρc最低值为1.42×10-3Ω.cm2;同条件下,80 nm Pt/p-GaN的ρc为6.63×10-3Ω.cm2,30 nm Cr/p-GaN的ρc为2.03×10-2Ω.cm2,且其合金前的ρc为5.74×10-2Ω.cm2,比合金后的ρc更高。这说明,Cr是更为理想的Ni/Ag保护材料,若Ni/Ag合金后再蒸Cr,效果更佳。最后,通过芯片老化实验,验证了Cr是一种较为理想的、可靠的反射镜保护材料,采用其制备的薄膜型功率芯片具有很高的可靠性。     

GaN蓝光LED电极接触电阻的优化

通过分析LED的工作电压和晶圆上两相邻N电极间电阻来讨论快速退火(RTA)和表面处理对GaN基蓝光LED接触电极的影响.研究了p-GaN表面处理对Ni/Au与p-GaN接触电阻的影响.结果表明,用KOH清洗p-GaN表面比用HCl清洗更能有效地改善Ni/Au与p-GaN的接触电阻.讨论了在氧和氮混合气氛下两种退火温度对P电极接触电阻的影响,当退火温度从570 ℃升到620 ℃时接触电阻升高.研究了氮气氛下不同退火温度和时间对LED电极接触的影响,发现在480 ℃下连续退火对N接触有利,但却使P接触变差,而450 ℃、10 min的氮气氛退火能同时得到较好P接触和N接触.     

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。     

p-GaN／Au欧姆接触的研究

本文对p-GaN/Au的接触电阻率进行了研究．用沸腾的王水处理p-GaN表面后,p-GaN/Au可直接形成电阻率为0．045Ω·cm~2的欧姆接触．接触电阻率测试和I-V特性曲线测试表明,在N_2气氛围中退火可影响p-GaN/Au接触电阻率的大小．在700℃温度下退火5min后,接触电阻率最小,其值为0．034Ω·cm~2,而在900℃温度下退火5min后,I-V特性曲线是非线性的。分析表明,在700℃温度下退火后,p-GaN/Au的界面间的反应使接触面增大,而在900℃温度下退火后,p-GaN表面的N会扩散到Au层里在p-GaN表面层产生N空位,这是p-GaN/Au接触电阻率变化的主要原因．     

p型GaN上Pd/NiO/Al/Ni反射电极欧姆接触的热稳定性研究

研究了p型GaN上Pd/NiO/Al/Ni反射电极欧姆接触的比接触电阻率、热稳定性,以及光学反射率。与传统Pd/Al/Ni电极相比,Pd/NiO/Al/Ni电极的欧姆接触在氮气环境中经300℃下热处理10min后,仍保持低比接触电阻率(小于5×10-4Ω·cm2)和高反射率(大于80%@365nm)。研究获得的优化Pd/NiO层厚度为1nm/2nm,此时的Pd/NiO/Al/Ni反射电极既能形成良好的欧姆接触,拥有低比接触电阻率,又能减少对紫外光的吸收,保持高反射率。研究表明适当的NiO层厚度能够有效地防止热处理过程中上层Al金属向p-GaN表面层的渗入,对于制备高质量的Al基反射电极至关重要。     

p型GaAs欧姆接触性能研究

为了研究半导体光电器件p-GaAs欧姆接触的特性,利用磁控溅射在p-GaAs上生长Ti厚度在10~50 nm范围、Pt厚度在30~60 nm范围的Ti/Pt/200 nm Au电极结构。利用传输线模型测量了具有不同的Ti、Pt厚度的Ti/Pt/200 nm Au电极结构接触电阻率,研究了退火参数对欧姆接触性能的影响,同时分析了过高温度导致电极金属从边缘向内部皱缩的机理。结果表明,Ti厚度为30 nm左右时接触电阻率最低,接触电阻率随着Pt厚度的增加而增加;欧姆接触质量对退火温度更敏感,退火温度达到510 ℃时电极金属从边缘向内部皱缩。采用40 nm Ti/40 nm Pt/200 nm Au作为半导体光电器件p-GaAs电极结构,合金条件为420 ℃,30 s可以形成更好的欧姆接触。     

Performance improvement in tensile-strained In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As metamorphic HEMT

This paper proposes a In/sub 0.5/Al/sub 0.5/As/In/sub x/Ga/sub 1-x/As/In/sub 0.5/Al/sub 0.5/As (x=0.3-0.5-0.3) metamorphic high-electron mobility transistor with tensile-strained channel. The tensile-strained channel structure exhibits significant improvements in dc and RF characteristics, including extrinsic transconductance, current driving capability, thermal stability, unity-gain cutoff frequency, maximum oscillation frequency, output power, power gain, and power added efficiency.     

Very low-noise Al/sub 0.3/Ga/sub 0.7/As/Ga/sub 0.65/In/sub 0.35/As/GaAs single quantum-well pseudomorphic HEMTs

AlGaAs/GaInAs/GaAs pseudomorphic HEMTs with an InAs mole fraction as high as 35% in the channel has been successfully fabricated. The device exhibits a maximum extrinsic transconductance of 700 mS/mm. At 18 GHz, a minimum noise figure of 0.55 dB with 15.0 dB associated gain was measured. At 60 GHz, a minimum noise figure as low as 1.6 dB with 7.6 dB associated gain was also obtained. This is the best noise performance yet reported for GaAs-based HEMTs.<>     

A 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode array

We report a 12 /spl times/ 12 In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As avalanche photodiode (APD) array. The mean breakdown voltage of the APD was 57.9 V and the standard deviation was less than 0.1 V. The mean dark current was /spl sim/2 and /spl sim/300 nA, and the standard deviation was /spl sim/0.19 and /spl sim/60 nA at unity gain (V/sub bias/ = 13.5 V) and at 90% of the breakdown voltage, respectively. External quantum efficiency was above 40% in the wavelength range from 1.0 to 1.6 /spl mu/m. It was /spl sim/57% and /spl sim/45% at 1.3 and 1.55 /spl mu/m, respectively. A bandwidth of 13 GHz was achieved at low gain.     

Al/sub 0.3/Ga/sub 0.7/As/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) doped-channel field-effect transistors (DCFET's)

The properties of both lattice-matched and strained doped-channel field-effect transistors (DCFET's) have been investigated in AlGaAs/In/sub x/Ga/sub 1-x/As (0/spl les/x/spl les/0.25) heterostructures with various indium mole fractions. Through electrical characterization of grown layers in conjunction with the dc and microwave device characteristics, we observed that the introduction of a 150-/spl Aring/ thick strained In/sub 0.15/Ga/sub 0.85/As channel can enhance device performance, compared to the lattice-matched one. However, a degradation of device performance was observed for larger indium mole fractions, up to x=0.25, which is associated with strain relaxation in this highly strained channel. DCFET's also preserved a more reliable performance after biased-stress testings.<>     

Morphological and electrical characterization of SixCryCzBv thin films

Si_xCr_yC_zB_v thin films with several compositions have been studied for integration of high precision resistors in 0.8 μm BICMOS technology. These resistors, integrated in the back-end of line, have the advantage to provide high level of integration and attractive electrical behavior in temperature, for analog devices. The film morphology and the structure have been investigated through transmission electron microscopy analysis and have been then related to the electrical properties on the base of the percolation theory. According to this theory, and in agreement with experimental results, negative thermal coefficient of resistance (TCR) has been obtained for samples with low Cr content, corresponding to a crystalline volume fraction below the percolation threshold.Samples with higher Cr content exhibit, instead, a variation of the TCR as a function of film thickness: negative TCR values are obtained for thickness lower than 5 nm, corresponding to a crystalline volume fraction below the percolation threshold; positive TCR are obtained for larger thickness, indicating the establishment of a continuous conductive path between the Cr rich grains. This property seems to be determinant in order to assure the possibility to obtain thin film resistors almost independent on the temperature.     

Highly linear Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMTs

We report an Al/sub 0.3/Ga/sub 0.7/N-Al/sub 0.05/Ga/sub 0.95/N-GaN composite-channel HEMT with enhanced linearity. By engineering the channel region, i.e., inserting a 6-nm-thick AlGaN layer with 5% Al composition in the channel region, a composite-channel HEMT was demonstrated. Transconductance and cutoff frequencies of a 1 /spl times/100 /spl mu/m HEMT are kept near their peak values throughout the low- and high-current operating levels, a desirable feature for linear power amplifiers. The composite-channel HEMT exhibits a peak transconductance of 150 mS/mm, a peak current gain cutoff frequency (f/sub T/) of 12 GHz and a peak power gain cutoff frequency (f/sub max/) of 30 GHz. For devices grown on sapphire substrate, maximum power density of 3.38 W/mm, power-added efficiency of 45% are obtained at 2 GHz. The output third-order intercept point (OIP3) is 33.2 dBm from two-tone measurement at 2 GHz.     

Comparison between Pt/TiO2/Pt and Pt/TaOX/TaOY/Pt based bipolar resistive switching devices

Nonvolatile memories have emerged in recent years and have become a leading candidate towards replacing dynamic and static random-access memory devices. In this article, the performances of TiO₂ and TaO₂ nonvolatile memristive devices were compared and the factors that make TaO₂ memristive devices better than TiO₂ memristive devices were studied. TaO₂ memristive devices have shown better endurance performances (10⁸ times more switching cycles) and faster switching speed (5 times) than TiO₂ memristive devices. Electroforming of TaO₂ memristive devices requires~4.5 times less energy than TiO₂ memristive devices of a similar size. The retention period of TaO₂ memristive devices is expected to exceed 10 years with sufficient experimental evidence. In addition to comparing device performances, this article also explains the differences in physical device structure, switching mechanism, and resistance switching performances of TiO₂ and TaO₂ memristive devices. This article summarizes the reasons that give TaO₂ memristive devices the advantage over TiO₂ memristive devices, in terms of electroformation, switching speed, and endurance.     

Electrooptic ferroelectric Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films

We report on waveguiding and electrooptic properties of epitaxial Na/sub 0.5/K/sub 0.5/NbO/sub 3/ films grown by radio-frequency magnetron sputtering on Al/sub 2/O/sub 3/(11_02) single crystal substrates. High optical waveguiding performance has been demonstrated in infrared and visible light. The in-plane electrooptic effect has been recorded in transmission using a transverse geometry. At dc fields, the effective linear electrooptic coefficient was determined to 28 pm/V, which is promising for modulator applications.