TiAl3 和Ti/TiAl3 非合金化电极n型GaN欧姆接触的实现

在不进行合金化的情况下,首次直接采用TiAl3合金材料作为金属接触电极.在蓝宝石衬底上生长的n型载流子浓度为2×1018 cm-3的GaN上,成功地得到低接触电阻的欧姆接触,并由环形传输线模型方法测得比接触电阻率为3×10-5 Ω*cm2.与通常n型欧姆接触采用的Ti/Al双层结构比较,TiAl3合金结构更容易形成非合金化的n型欧姆接触.在此实验基础上,进一步分析了N空位和界面层处的TiAl3在形成非合金化或低温退火欧姆接触中发挥的作用,由此设计的Ti/TiAl3/Ni/Au接触结构,在TiAl3合金结构基础上明显地降低了接触电阻率.     

GaN基紫光LED的高反射率p型欧姆接触

研究用于GaN基大功率倒装焊(Flip-chip)紫光LED(UV-LED)的高反射率p型欧姆接触的电学和光学性能。用磁控溅射的方法在GaN基LED外延片表面沉积了不同厚度Ag,Al,Au和Pd四种金属,测量了样品的反射率和透射率。结合同步辐射高强度X射线衍射和AFM对金属薄膜的晶体结构进行分析,并对表面形貌进行了观测,对由金属薄膜构成的多层膜结构及其对光反射率的作用机理进行了研究。测量结果表明,在入射光波长为400nm时,Ni/Au/Ag和Ni/Au/Al电极的反射率比Ni/Au的反射率提高了三倍。同时与p-GaN有良好的欧姆接触特性。     

用卢瑟福背散射/沟道技术及高分辨X射线衍射技术分析不同Al和In含量的AlInGaN薄膜的应变

利用卢瑟福背散射/沟道技术对在蓝宝石衬底上用金属有机化学气相沉积方法生长的有GaN缓冲层(>2μm)的一系列不同Al和In含量的AlInGaN薄膜进行组分及结晶品质的测量；并结合高分辨X射线衍射技术，通过对AlInGaN的对称(0002)面，及非对称(1015)面的θ—2θ扫描及倒空间扫描，可以精确测定AlInGaN外延层的晶格常数及水平和垂直方向的应变.实验结果表明AlInGaN 薄膜中不同含量Al和In对其应变有较大的影响，结合Vegard定理，对这一现象给出了理论的解释. 关键词： AlInGaN 高分辨X射线衍射 卢瑟福背散射/沟道 弹性应变     

表面化学处理和退火对p-GaN/ZnO:Ga接触特性的影响

ZnO∶Ga(GZO)透明电极沉积在p-GaN表面,用作透明电流扩展层。直接沉积在p-GaN上的p-GaN/GZO存在较大的势垒,容易形成肖特基接触,而良好的欧姆接触对功率LED器件至关重要。为了降低接触势垒,采用盐酸和氢氧化钠溶液对GaN表面进行去氧化层处理,并对p-GaN/GZO进行退火处理,研究表面处理和退火对p-GaN/GZO接触特性的影响。研究表明:碱性溶液处理有利于降低接触势垒;退火处理后,接触势垒略有增加。     

ZnMgO/n-ZnO/ZnMgO/p-GaN异质结LED的紫外电致发光

利用等离子体辅助分子束外延( P-MBE)技术制备了ZnMgO/n-ZnO/ZnMgO/p-GaN异质结LED.Ni/Au电极与p-GaN、In电极与ZnMgO之间都形成了良好的欧姆接触.在ZnMgO/n-ZnO/ZnMgO/p-GaN异质结器件中观察到了明显的整流特性.异质结的电致发光强度随着注入电流的增大而逐渐增强...     

高反射率p-GaN欧姆接触电极

根据光学薄膜原理计算了GaN/Ti/Ag、GaN/Al和GaN/Ni/Au/Ti/Ag、GaN/Ni/Au/Al多层电极结构的反射率,得出Ag基和Al基反射电极均能在全角范围内提供较高的反射率。实验测量结果表明,反射率能高于80%的Ag基反射电极,具有低欧姆接触的电学特性。并将GaN/Ni/Au/Ti/Ag多层反射电极应用在上下电极结构的GaN基LED中。实验上采用两步合金法获得了低接触电阻、高反射率的电极结构,并引入Ni/Au覆盖层克服了Ag高温时的团聚和氧化现象。解决了Ag电极的稳定性问题,显著地提高了LED的出光效率,成功制备了具有上下电极结构的GaN基LED管芯。     

Pd/p-GaN欧姆接触退化机理

近几年,Ⅲ-Ⅴ族半导体GaN由于其宽直接带隙,在高温、高功率器件方面得到了广泛研究。但是,目前GaN器件的性能依然受到了p型欧姆接触性能不良的限制,在长期使用过程或高温环境中激光器等器件性能退化严重。因此,获得性能优异的p-GaN接触仍然是一个巨大的挑战。虽然Pd基的金属体系已然在p-GaN获得了欧姆接触,但是Pd与GaN接触之后的微观结构及其高温特性尚不为人知。本文针对常用于p型GaN接触的第一层金属Pd材料,讨论了Pd/p-GaN接触界面的特性和退化机制。通过四探针测试仪、X射线光电子能谱(XPS)和原子力显微镜(AFM)实验测试和分析对比,发现Pd/p-GaN界面受到氧气和温度影响的退化过程。高温退火在界面处促成Ga-Pd合金相生成利于形成良好的接触,但是在有氧参与的情况下,金属的氧化反应超越其他因素成为主导,致使界面和性能发生明显的退化。温度越高退化越严重,甚至表面形貌状态完全改变,由平滑的原子台阶形貌转化呈现出树枝状晶粒状态。因此,保持Pd与p-GaN界面清洁、控制界面的氧成分不仅是形成合金态获得良好接触的关键,而且也关系着器件的长期稳定和可靠,是防止器件性能衰减和退化要害所在。     

多层Ti/Al电极结构对Ga N/AlGaN HEMT欧姆接触特性的影响

研究了多层Ti/Al结构电极对GaN/AlGaN HEMT欧姆接触特性及表面形态的影响。采用传输线模型对各结构电极的比接触电阻率进行了测量,采用扫描电子显微镜对电极表面形态进行扫描。实验结果显示,在同样的退火条件下,随着Ti/Al层数的增加,比接触电阻率逐渐减小,表面形态趋于光滑;降低Ti/Al层的厚度会加剧Au向内扩散而增加比接触电阻率,但能稍微改善表面形态;Ti比例过高会影响Ti N的形成导致比接触电阻率增加,但能明显改善表面形态。     

感应耦合等离子体刻蚀p-GaN的表面特性

研究了p-GaN材料经感应耦合等离子体(ICP)刻蚀后的表面特性,并用不同的方法对刻蚀表面进行处理.利用原子力显微镜(AFM)和X射线光电子能谱(XPS)对刻蚀样品进行分析,并在样品表面制作Ni/Au电极,进行欧姆接触特性的测试.实验结果表明了NaOH溶液处理表面对改善材料表面和欧姆接触特性是比较有效的. 关键词： GaN 感应耦合等离子刻蚀 表面处理 欧姆接触     

低接触电阻率Ni/Ag/Ti/Au反射镜电极的研究

研究了Ag的厚度、退火时间、沉积温度对于Ni/Ag/Ti/Au电极的反射率及与p-GaN欧姆接触性能的影响. 利用分光光度计测量反射率, 采用圆形传输线模型计算比接触电阻率. 结果表明: 随着Ag厚度的增加, Ni/Ag/Ti/Au电极的反射率逐渐增大; 在氧气氛围中, 随着退火时间从1 min增至10 min, 300 ℃退火时, 比接触电阻率持续下降, 而对于400-600 ℃退火, 比接触电阻率先减小后增大; 在300和400 ℃氧气中进行1-10 min 的退火后, Ni/Ag/Ti/Au的反射率变化较小, 退火温度高于400 ℃时, 随着退火时间的增加, 反射率急剧下降; 在400 ℃氧气中3 min退火后, 比接触电阻率可以达到3.6×10^-3 Ω·cm². 此外, 适当提高沉积温度可以增加Ni/Ag/Ti/Au的反射率并降低比接触电阻率, 沉积温度为120 ℃条件下的Ni/Ag/Ti/Au电极在450 nm处反射率达到90.1%, 比接触电阻率为6.4×10^-3 Ω·cm². 综合考虑电学和光学性能, 在沉积温度为120 ℃下蒸镀Ni/Ag/Ti/Au (1/200/100/100 nm)并在400 ℃氧气中进行3 min退火可以得到较优化的电极. 利用此电极制作的垂直结构发光二极管在350 mA电流下的工作电压为2.95 V, 输出光功率为387.1 mW, 电光转换效率达到37.5%.     

Auger electron spectroscopy of Au/NiOx contacts on p-GaN annealed in N2 and O2 + N2 ambients

We have designed a promising contact scheme to p-GaN. Au/NiO_x layers with a low concentration of O in NiO_x are deposited on p-GaN by reactive dc magnetron sputtering and annealed in N₂ and in a mixture of O₂ + N₂ to produce low resistivity ohmic contacts. Annealing has been studied of NiO_x layers with various contents of oxygen upon the electrical properties of Au/NiO_x/p-GaN. It has been found that the Au/NiO_x/p-GaN structure with a low content of oxygen in NiO_x layer provides a low resistivity ohmic contact even after subsequent annealing in N₂ or O₂ + N₂ ambient at 500 °C for 2 min.Auger depth profiles and transmission electron microscopy (TEM) micrographs reveal that while annealing in O₂ + N₂ ambient results in reconstruction of the initial deposited Au/NiO_x/p-GaN contact structure into a Au/p-NiO/p-GaN structure, annealing in N₂ brings about reconstruction into Au/p-NiO/p-GaN and Ni/p-NiO/p-GaN structures. Hence, in both cases, after annealing in N₂ as well as in O₂ + N₂ ambient, the ohmic properties of the contacts are determined by creation of a thin oxide layer (p-NiO) on the metal/p-GaN interface. Higher contact resistivities in the samples annealed in O₂ + N₂ ambient are most likely caused by a smaller effective area of the contact due to creation of voids.     

Use of TiB2 diffusion barriers for Ni/Au ohmic contacts on p-GaN

The use of a TiB₂ diffusion barrier for Ni/Au contacts on p-GaN is reported. The annealing temperature (25-950 °C) dependence of ohmic contact characteristics using a Ni/Au/TiB₂/Ti/Au metallization scheme deposited by sputtering were investigated by contact resistance measurements and auger electron spectroscopy (AES). The as-deposited contacts are rectifying and transition to ohmic behavior for annealing at ≥500 °C . A minimum specific contact resistivity of ∼3 × 10⁻⁴ Ω cm⁻² was obtained after annealing over a broad range of temperatures (800-950 °C for 60 s). The contact morphology became considerably rougher at the higher end of this temperature range. AES profiling showed significant Ti and Ni outdiffusion through the TiB₂ at 800 °C. By 900 °C the Ti was almost completely removed to the surface, where it became oxidized. Use of the TiB₂ diffusion barrier produces superior thermal stability compared to the more common Ni/Au, whose morphology degrades significantly above 500 °C.     

退火温度和退火气氛对Ni/Au与p-GaN之间欧姆接触性能的影响

研究了不同退火温度和气氛对Ni/Au与p-GaN之间欧姆接触性能的影响. 采用圆形传输线模型方法得到不同退火温度和不同退火气氛下的比接触电阻率. 结果表明, 较适宜的退火温度为500 ℃左右, 退火温度太高或太低都会导致比接触电阻率的增大; 较适宜的退火气氛为适量含氧的氮气气氛, 且氧气含量对比接触电阻率大小的影响并不显著. 经过对退火条件的优化, 得到的比接触电阻率可达7.65×10^-4 Ω·cm². 关键词： p-GaN 欧姆接触 圆形传输线模型 快速热退火     

Ni/Au与N掺杂p型ZnO的欧姆接触

研究了Au,In,Ni/Au三种不同金属膜与N掺杂p型ZnO的接触特性,发现Ni/Au双层膜更适合作为其欧姆电极材料,并比较了不同气氛和不同温度退火对Ni/Au电极的影响.发现在O₂中退火电极性能发生蜕变,而在N₂中退火性能得到改善.指出即使在N₂中退火,退火温度的选择也是至关重要的,本实验在400℃,氮气气氛下退火150s,得到了较好的欧姆接触特性.     

The effect of a surface layer capping p-InGaN/p-GaN superlattices on the contact to p-GaN

In this study, the influence of the surface layer (p-InGaN or p-GaN) capping p-InGaN/p-GaN superlattices (SLs) on the contact to p-type GaN was investigated. It was found that the specific contact resistance (_ρc)$\left({\rho }_c\right)$ to p-type GaN is lower when using p-InGaN as the surface layer. The lowest value of _ρc${\rho }_c$ was 1.99×10⁻⁴ Ω cm² at room temperature. It was also found that low temperature growth of the p-GaN layers in the SLs is beneficial for lowering the ohmic contact resistance. Unlike Ni/Au deposited directly on p-GaN (without the strained p-InGaN/p-GaN SLs), Ni/Au deposited on p-InGaN/p-GaN SLs produces ohmic behavior even before annealing.     

Study of Ti/Au,Ti/Al/Au,and Ti/Al/Ni/Au ohmic contacts to <Emphasis Type="Italic">n</Emphasis>-GaN

The contacts of Ti/Au, Ti/Al/Au, and Ti/Al/Ni/Au films deposited on n-GaN were studied by current–voltage (I–V) and transmission-line-method measurements. The effect of annealing temperature on specific contact resistivity has been investigated by changing the annealing temperature from 400 to 900 °C. Ti/Al/Au and Ti/Al/Ni/Au films were superior to the bilayer (Ti/Au) in ohmic contact characteristics and thermal stability. The Ti/Al/Ni/Au composite showed the best thermal stability due to the fact that Ni plays a more important role than the alloy of Ti/Al in preventing the interdiffusion of Ti, Al, and Au. The lowest contact resistivity (10^-7cm²) to n-GaN was obtained for the Ti/Al/Ni/Au sample by short-time/high-temperature annealing. The formation mechanism of ohmic contacts to n-GaN is also discussed. PACS 73.40.Cg; 73.61.Ey     

ZrB2-based Ohmic contacts to p-GaN

The annealing temperature dependence of contact resistance and layer stability of ZrB₂/Ti/Au and Ni/Au/ZrB₂/Ti/Au Ohmic contacts on p-GaN is reported. The as-deposited contacts are rectifying and transition to Ohmic behavior for annealing at ≥750 °C, a significant improvement in thermal stability compared to the conventional Ni/Au Ohmic contact on p-GaN, which is stable only to <600 °C. A minimum specific contact resistance of ∼2 × 10⁻³ Ω cm⁻² was obtained for the ZrB₂/Ti/Au after annealing at 800 °C while for Ni/Au/ZrB₂/Ti/Au the minimum value was 10⁻⁴ Ω cm⁻² at 900 °C. Auger Electron Spectroscopy profiling showed significant Ti, Ni and Zr out diffusion at 750 °C in the Ni/Au/ZrB₂/Ti/Au while the Ti and Zr intermix at 900 °C in the ZrB₂/Ti/Au. These boride-based contacts show promise for contacts to p-GaN in high temperature applications.