大功率倒装结构GaN LED p电极研究

从接触电阻、反射率、电流扩展等方面对Ni/Au/Ag,ITO/Ag,Ag等多种倒装结构p电极金属体系进行分析比较,给出了实现倒装结构大功率GaN LED p电极的多种设计方案.指出Ni/Au金属化体系在大功率LED应用中存在的热稳定性问题及Ru,Ir等新型金属体系实现GaN p电极接触的潜在优势.     

大功率倒装结构GaN LED p电极研究

从接触电阻、反射率、电流扩展等方面对Ni/Au/Ag,ITO/Ag,Ag等多种倒装结构p电极金属体系进行分析比较,给出了实现倒装结构大功率GaN LED p电极的多种设计方案.指出Ni/Au金属化体系在大功率LED应用中存在的热稳定性问题及Ru,Ir等新型金属体系实现GaN p电极接触的潜在优势.     

正装、倒装结构GaN 基LED提取效率分析

从几何和物理光学角度分析了影响GaN基LED提取效率的因素,并以理论分析为基础,利用Monte-Carlo光线追踪的方法,对GaN基LED的提取效率进行模拟,比较不同器件结构对LED提取效率的影响.模拟结果表明,采用倒装结构可以显著提高GaN基LED的提取效率,Ni/Au透明电极透射率为0.6～0.9时,相对于普通正装结构,倒装结构可以使LED提取效率提高39%～16%.     

垂直结构GaN基LED用Ni/Ag反射镜电极

Ni/Ag/Ti/Au金属系反射镜电极广泛用于GaN基垂直结构发光二极管(LED)的传统制造工艺.这种电极需要进行高温长时间整体退火才能获得高质量的欧姆接触,但对电极的反射率和器件性能影响较大.介绍了一种新工艺方法,该方法将电极分解为接触层和反射层,降低反射层经历的退火温度和时间,获得了拥有良好的欧姆接触特性和高反射率的反射镜电极,解决了传统电极光学性能和电学性能相互制约的问题.首先生长极薄的Ni/Ag作为接触层,对接触层进行高温长时间退火后再生长厚层Ag作为反射层,之后再进行一次低温退火.使得对反射起主要作用的反射层免于高温长时间退火,相较于传统Ni/Ag/Ti/Au电极,该方法在获得更优良的欧姆接触的同时,提升了电极的反射率.在氧气氛围下进行500℃接触层退火3 min,400℃整体退火1 min后,电极的比接触电阻率为1.7×l0-3Ω·cm2,同时在450 nm处反射率为93％.     

p型GaN的Ni/Au合金电极的I-V特性

运用传输线方法(TLM)测量了p型GaN合金后的Ni/Au电极的接触电阻率和电流-电压(I-V)关系,推导了合金的Ni/Au电极和p型GaN接触处的电流密度与电压(J-V)的关系.在考虑热发射机制和镜像力的基础上,通过对p型GaN的Ni/Au合金电极的I-V特性分析,进一步得出势垒高Φb=0.41eV,受主浓度Na=4×1019cm-3,能带弯曲Vi=0.26V,和EF-Ev:0.15eV.这些结果与理论值和其他实验结果符合得很好.     

p型GaN的Ni/Au合金电极的I-V特性

运用传输线方法(TLM)测量了p型GaN合金后的Ni/Au电极的接触电阻率和电流-电压(I-V)关系,推导了合金的Ni/Au电极和p型GaN接触处的电流密度与电压(J-V)的关系.在考虑热发射机制和镜像力的基础上,通过对p型GaN的Ni/Au合金电极的I-V特性分析,进一步得出势垒高Φb=0.41eV,受主浓度Na=4×1019cm-3,能带弯曲Vi=0.26V,和EF-Ev:0.15eV.这些结果与理论值和其他实验结果符合得很好.     

GaN外延材料测试技术的研究

分别用金属In和Ti/Al/Ni/Au合金层制备GaN HEMT结构外延片的霍尔测试电极,并对样品进行霍尔测试.发现In金属与外延片形成非欧姆接触,Ti/Al/Ni/Au合金层与外延片形成良好的欧姆接触.用电化学C-V方法测试样品,得到的载流子浓度与合金电极制备的样品经霍尔测试得到的载流子浓度一致,从而验证了此种霍尔测试方法的准确性,为GaN外延材料的测试提出了准确可行的测试方法.     

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。     

石墨烯/NiAu复合透明导电层在GaN LED的应用

通过溅射方法制备Ni/Au层,用作石墨烯和p型GaN之间的插入层来减小接触电势。研究了Ni和Au的厚度比与GaN LED性能的关系。结果表明,在1.5 nm总厚度的条件下,Ni与Au厚度比为1 nm/0.5 nm时为最佳,可同时兼顾透光性能和良好欧姆接触,此时,石墨烯/NiAu复合透明导电层可以明显地降低GaN LED的工作电压,同时在蓝光波段具有很高的透光率,因而提高了GaN LED的发光性能。     

AlGaN/GaN异质结构的欧姆接触

通过改变Ti/Al的结构及退火条件,研究了AlGaN/GaN异质结构上Ti/Al/Ni/Au金属体系所形成的欧姆接触.结果表明,Ti/Al/Ni/Au金属厚度分别为20,120,55和45nm,退火条件为高纯N2气氛中850℃、30s时在AlGaN/GaN异质结构上获得了良好的欧姆接触,其比接触电阻率为3.30×10-6Ω·cm2.SEM分析表明该条件下的欧姆接触具有良好的表面形貌,可以很好地满足高性能AlGaN/GaN高电子迁移率晶体管制造的要求.     

Interface observation in Au/Ni/p-GaN studied by HREM and energy-filtering TEM

The contact resistance of Au/Ni/p-GaN ohmic contacts for different annealing conditions was measured. This was then correlated with microstructure, including phase distribution, observed by high-resolution electron microscopy combined with energy-filtering imaging. A contact resistance of 2.22 x 10(-4) ohms cm2 for Au/Ni contacts to p-GaN after annealing at 500 degrees C for 5 min in air ambient was obtained. NiO layers were identified at the interface and upper area of annealed Ni/Au/p-GaN for air ambient. In addition, an Au layer was found at the interface of p-GaN due to a reversal reaction during annealing. Identification of the observed phases is discussed, along with possible formation mechanisms for the ohmic contacts in the Au/Ni/p-GaN system.     

氧化对 GaN 基LED透明电极接触特性的影响

研究了热退火对InGaN/GaN 多量子阱LED的Ni/Au-p-GaN欧姆接触的影响.发现在空气和 N2气氛中交替地进行热退火的过程中Ni/Au接触特性显示出可逆现象. Ni/Au-p-GaN接触的串联电阻在空气中随合金化时间逐渐减小,在随后的 N2 中的热退火后会使该串联电阻增加,但在空气中再次热退火能使接触特性得到恢复.同时对Ni/Au-p-GaN 接触在空气中合金化过程中的层反转的成因进行了讨论.     

表面处理对p-GaN欧姆接触的影响

分别用稀盐酸、王水以及(NH4)2S溶液处理p-GaN表面,通过测试样品表面Ols的X射线光电子能谱(XPS),比较了这些溶液去除p-GaN表面氧化层的能力;在经不同溶液处理后的样品表面,以相同的条件制作Ni/Au电极,并测试其与p-GaN的比接触电阻,结果表明经稀盐酸处理后的样品表面,由于其氧含量较高,不能与Ni/Au形成良好的欧姆接触,而经王水和(NH4)2S溶液处理后的p-GaN表面,能与Ni/Au形成良好的欧姆接触;最后,通过比较样品表面的Ga/N原子浓度比,探讨了王水处理p-GaN表面能够形成良好欧姆接触的原因.     

Thermally stable Ge/Ag/Ni Ohmic contact for InAlAs/InGaAs/InP HEMTs

Excellent annealed ohmic contacts based on Ge/Ag/Ni metallization have been realized in a temperature range between 385 and 500/spl deg/C, with a minimum contact resistance of 0.06 /spl Omega//spl middot/mm and a specific contact resistivity of 2.62 /spl times/10/sup -7/ /spl Omega//spl middot/cm/sup 2/ obtained at an annealing temperature of 425/spl deg/C for 60 s in a rapid thermal annealing (RTA) system. Thermal storage tests at temperatures of 215 and 250/spl deg/C in a nitrogen ambient showed that the Ge/Ag/Ni based ohmic contacts with an overlay of Ti/Pt/Au had far superior thermal stabilities than the conventional annealed AuGe/Ni ohmic contacts for InAlAs/InGaAs high electron mobility transistors (HEMTs). During the storage test at 215/spl deg/C, the ohmic contacts showed no degradation after 200 h. At 250/spl deg/C, the contact resistance value of the Ge/Ag/Ni ohmic contact increased only to a value of 0.1 /spl Omega//spl middot/mm over a 250-h period. Depletion-mode HEMTs (D-HEMTs) with a gate length of 0.2 /spl mu/m fabricated using Ge/Ag/Ni ohmic contacts with an overlay of Ti/Pt/Au demonstrated excellent dc and RF characteristics.     

Ohmic contacts to n-type GaN

Ohmic contacts to n-GaN using Ag, Au, TiN, Au/Ti, Au/Mo/Ti, and Au/Si/Ti have been studied. The Fermi level of GaN appears to be unpinned, and metals and compounds with work functions less than the electron affinity resulted in ohmic contacts. Reactively sputter deposited TiN was ohmic as deposited. However, Au/Ti, Au/Mo/Ti, and Au/Si/Ti required heat treatments to form ohmic contacts, with the best being an RTA at 900°C. Ag and Au were shown to diffuse across the GaN surface at T>500°C; therefore, they are unstable, poor ohmic contact metallizations as single metals. The other contact schemes were thermally stable up to 500°C for times of 30 min.     

The characteristics of AuGe-based ohmic contacts to n-GaAs including the effects of aging

We have investigated and compared the characteristics of Au:Ge, Ni/Au:Ge and Au/Ni/Au:Ge ohmic contact metallizations to ion-implanted and epitaxial n-GaAs layers on semi-insulting substrates. Auger depth profiles of ohmic contacts and SEM of surface microstructures have provided significant insight as to the nature and degradation mechanism of ohmic contacts with aging. An electrolytic tank model with distributed resistors representing nodular or cluster form contacts has been successfully used to understand the effects of non-uniform ohmic contacts. A small degree of change in the semiconductor sheet resistance in the gaps between contacts, with aging at an elevated temperature, has been attributed to possible lateral surface diffusion of Au in the Au:Ge contacts and Ge in the Ni/Au:Ge and Au/Ni/Au:Ge contacts.     

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.     

Calculations and measurements of contact resistance of semi-transparent Ni/Pd contacts to p-GaN

Calculations of specific contact resistance as a function of doping and barrier height were performed for p-type GaN. These calculations took into account two valence bands, each with different effective masses, and show that at low doping, the heavy hole band accounts for most of the conduction, whereas at heavier doping, the light hole band dominates conduction. These calculations also indicate the barrier height for typical contacts to p-GaN is between 0.75 eV and 1 eV. Specific contact resistance measurements were made for oxidized Ni/Au, Pd, and oxidized Ni/Pd ohmic contact metal schemes to p-GaN. The Ni/Pd contact had the lowest specific contact resistance, 6×10⁻⁴ Ω cm². Auger sputter depth profile analysis showed some Ni diffused away from the GaN surface to the contact surface with the bulk of the Pd located in between two areas of Ni. Both Ni and Pd interdiffused with the GaN at the semiconductor surface. The majority of the oxygen observed was with the Ni as NiO. Angle-resolved-x-ray photoelectron spectroscopy (AR-XPS) analyses showed the formation of predominantly NiO and PdO species, with higher Ni and Pd oxides at the contact surface.     

The improvement of electrical properties of Pd-based contact to p-GaN by surface treatment

The surface treatment effect on the interfacial reaction and electrical property of Au/Pd contacts to p-GaN has been investigated. The contact resistance of Au/Pd contacts on boiling aqua regia treated p-GaN was lower than aqua regia treated p-GaN by one order of magnitude. The specific contact resistivity of Au/Pd contacts on boiling aqua regia treated p-GaN increased with annealing temperature, but that on aqua regia treated p-GaN decreased with annealing temperature and it showed minimum value after annealing at 700°C. According to the results of the interfacial reaction, the Au/Pd contact metals reacted more easily with aqua regia treated p-GaN than boiling aqua regia treated p-GaN. X-ray photoelectron spectroscopy analysis revealed that the relative surface Ga-to-N ratio of boiling aqua regia treated p-GaN was lower than that of aqua regia treated p-GaN and the surface of p-GaN was modified from Ga-termination to N-termination by surface treatment using boiling aqua regia. According to the results of surface analysis and interfacial reaction of Au/Pd/p-GaN, it could be concluded that the different temperature dependence of contact resistance according to the surface treatment conditions was related strongly to the surface modification of p-GaN from Ga-termination to N-termination.