n型GaN欧姆接触的研究进展

Ⅲ-Ⅴ族GaN基材料以其在紫外光子探测器、发光二极管、高温及大功率电子器件等方面的应用潜能而被广为研究.其中,低阻欧姆接触是提高GaN基器件光电性能的关键.金属/GaN界面上较大的欧姆接触电阻一直是影响器件性能及可靠性的一个问题.对于各种应用来说, GaN的欧姆接触需要得到改进.通过对相关文献的归纳分析,本文主要介绍了近年来在改进n-GaN工艺,提高欧姆接触性能等方面的研究进展.     

AlGaN器件欧姆接触的研究进展

作为制备光电子器件例如紫外光子探测器、异质结场效应晶体管(HFET)、高电子迁移率晶体管(HEMT)异质结场效应管等的一种宽禁带半导体材料, III V 族氮化物AlGaN器件近年来颇受关注.AlGaN与金属之间的低阻欧姆接触的实现问题阻碍了AlGaN(基)器件的发展.通过对相关文献的归纳分析,介绍了近年来AlGaN器件在欧姆接触形成、金属化方案、合金化工艺及表面处理等方面的研究进展.     

Si基GaN射频器件研究进展

针对低成本、大尺寸的GaN HEMT技术,回顾了近年来Si基GaN射频器件在大尺寸材料外延生长、器件制备工艺与单片集成电路等方面的国内外研究进展,指出推进其发展的重要意义,并分析了抑制射频损耗、无金欧姆接触及复合钝化等技术难点,阐明了具有研究前景的优化及发展方向.基于高阻Si衬底上AlGaN/GaN HEMT结构,通过...     

基于选择性湿法粗化方法制作n型欧姆接触的垂直结构发光二极管的电学性能研究

低阻和高稳定性的氮极性面N型欧姆接触对于GaN基垂直结构发光二极管尤为重要。研究发现,相对于未湿法粗化N型GaN面,湿法粗化N型GaN面的欧姆接触电阻较大,且最终制成的发光二极管具有较高的开启电压和较低的反向漏电。本文提出了一种选择性湿法粗化方法制作氮极性面N型GaN欧姆接触,基于此方法最终制成的垂直结构发光二极管具有更低的开启电压和反向漏电,并且输出光功率略有提升。进一步的老化实验表明该法制作的欧姆接触具有良好的稳定性。     

GaN基增强型HEMT器件的研究进展

随着电力转换系统功率密度和工作频率的不断提高,需要开发性能优于传统半导体的功率器件。作为第三代半导体材料的典型代表,氮化镓（GaN）被认为是提高大功率电力系统转换效率的新一代功率器件的主要候选材料。在操作类型方面,增强型（也称为常关型）器件具有安全、能简化电路设计以及更优的电路拓扑设计等优势,在行业应用中更具吸引力。总结并对比了目前国际上主流的GaN基增强型器件的结构和制备工艺,着重介绍了基于栅凹槽结构的功率器件技术,特别是栅槽刻蚀后的界面处理、栅介质层的优化技术。围绕器件的关键指标,总结了材料外延结构、欧姆接触、场板以及钝化工艺对器件性能的影响,提出了未来可能的技术方案。     

fT为350 GHz的InAlN/GaN HFET高频器件研究

采用再生长n+ GaN非合金欧姆接触工艺研制了具有高电流增益截止频率(fT)的InAlN/GaN异质结场效应晶体管 (HFETs),器件尺寸得到有效缩小,源漏间距减小至600 nm.通过优化干法刻蚀和n+ GaN外延工艺,欧姆接触总电阻值达到0.16 Ω·mm,该值为目前金属有机化学气相沉积(MOCVD)方法制备的最低值.采用自对准电子束曝光工艺实现34 nm直栅.器件尺寸的缩小以及欧姆接触的改善,器件电学特性,尤其是射频特性得到大幅提升.器件的开态电阻(Ron)仅为0.41 Ω·mm,栅压1 V下,漏源饱和电流达到2.14 A/mm.此外,器件的电流增益截止频率(fT)达到350 GHz,该值为目前GaN基HFET器件国内报道最高值.     

GaN基发光二极管的可靠性研究进展

高效高亮度GaN基发光二极管(LED)在图像显示、信号指示、照明以及基础研究等方面有着极为广阔的应用前景,器件的可靠性是实现其广泛应用的保证.本文从封装材料退化、金属的电迁移、p型欧姆接触退化、深能级与非辐射复合中心增加等方面介绍了GaN基LED的退化机理以及提高器件可靠性的措施,并对GaN基LED的应用前景进行了展望.     

p型GaN欧姆接触的研究进展

宽带隙的GaN作为半导体领域研究的热点之一,近年来发展得很快.p型GaN的欧姆接触问题一直阻碍高温大功率GaN基器件的研制.本文讨论了金属化方案的选择、表面预处理和合金化处理等几个问题,回顾了近年来p型GaN欧姆接触的研究进展.     

Si基GaN HEMT低温欧姆接触工艺研究

研究了在Si基GaN外延材料上实现低温欧姆接触的技术途径。研究了外延层的刻蚀深度、合金温度以及不同金属体系对接触特性的影响,发现外延层刻蚀深度的优化可显著改善欧姆接触特性。采用Ti/Al(10/200nm)金属,在外延层刻蚀深度为20nm以及合金温度550°C时,得到接近传统高温合金条件下的接触电阻,最小值达到0.76Ω.mm,同时实现的欧姆接触电极具有良好的形貌。该技术有望应用于高频、高功率GaN HEMT的工艺。     

氧化铟锡与掺Fe半绝缘GaN的接触特性

氧化铟锡(ITO)透明电极能够有效提高GaN光导半导体开关的光吸收效率和电场均匀性,但如何在透明电极ITO与半绝缘GaN之间实现良好的欧姆接触是一个难题.通过在ITO和半绝缘GaN之间插入与GaN功函数相近的Ti薄层,并利用快速热退火过程加速Ti与GaN之间的反应.研究发现Ti薄层的厚度和退火温度对欧姆接触有重要影响.在Ti薄层厚度为5 nm时,随着退火温度的升高,ITO/Ti/GaN之间的接触逐渐转变为欧姆接触,且接触电阻率随之减小;但当退火温度超过700℃时,欧姆接触变差,这与ITO中的In、Sn和O元素向界面扩散有关;适当提高Ti薄层的厚度可以有效改善ITO/Ti/GaN欧姆电极的热稳定性,但过厚的Ti薄层会对GaN基光电器件的透过率产生影响.     

Ohmic-Contact Technology for GaN-Based Light-Emitting Diodes: Role of P-Type Contact

GaN-based semiconductors are of great technological importance for the fabrication of optoelectronic devices, such as light-emitting diodes (LEDs) and laser diodes. The further improvement of LED performance can be achieved through the enhancement of external quantum efficiency. In this regard, high-quality p-type ohmic electrodes having low contact resistance and high transmittance (or reflectivity), along with thermal stability, must be developed because p-type ohmic contacts play a key role in the performance of LEDs. In this paper, we review recent advances in p-type ohmic-contact technology for GaN-based LEDs. A variety of methods for forming transparent and reflective ohmic contacts are introduced.     

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.     

Improvement of InGaN-GaN light-emitting diodes with surface-textured indium-tin-oxide transparent ohmic contacts

Presents a surface-textured indium-tin-oxide (ITO) transparent ohmic contact layer on p-GaN to increase the optical output of nitride-based light-emitting diodes (LED) without destroying the p-GaN. The surface-textured ITO layer was prepared by lithography and dry etching, and dimensions of the regular pattern were approximately 3 /spl times/ 3 /spl mu/m. The operating voltage of the surface-textured LED was almost the same as that of the typical planar LED since the ITO layer was in ohmic contact with the p-GaN. The experimental results indicate that the surface-textured ITO layer is suitable for fabricating high-brightness GaN-based light emitting devices.     

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.     

掺杂GaN的湿法刻蚀研究

对掺杂GaN的湿法刻蚀研究进行了总结,回顾了不同的湿法刻蚀技术,包括传统的酸碱化学刻蚀和电化学刻蚀。从掺杂GaN的生长过程、表面化学组分和光电性质出发,深入地分析了湿法刻蚀的特性,对比了不同刻蚀方法的原理和效果。考虑到p-GaN的表面氧化层比较厚,接触电阻较大,能带向下弯曲不能进行光增强湿法刻蚀,重点阐述了p-GaN的传统湿法刻蚀和n-GaN的紫外光增强湿法刻蚀技术。与传统化学刻蚀相比,光增强湿法刻蚀具有更为广阔的前景。结合GaN基半导体器件的制作,对湿法刻蚀的主要应用进行了较为详细的归纳。目前,湿法刻蚀和干法刻蚀可以有效结合。将来湿法刻蚀有希望代替干法刻蚀。     

Reversible Degradation of Ohmic Contacts on p-GaN for Application in High-Brightness LEDs

This paper analyzes the high-temperature long-term stability of ohmic contacts on p-type gallium nitride (p-GaN). The contributions of the ohmic contacts and semiconductor material degradation are separated by adopting the transmission line method (TLM). Before stress, the current-voltage (I-V) curves measured at the pads of the TLMs showed a linear shape, indicating a good ohmic behavior of the contacts. Thermal treatment at 250degC was found to induce the worsening of the electrical characteristics of the contacts: identified degradation modes consist of a shift of the I-V curves toward higher voltages and strong nonlinearity of the characteristics around zero. This paper shows that the high-temperature instabilities of ohmic contacts on p-GaN are related to the interaction between the device surface and the plasma-enhanced chemical vapor deposition SiN passivation layer. Hydrogen contained in the passivation layer is supposed to play an important role in the degradation process: the interaction with the acceptor dopant at the metal/semiconductor interface induces the decrease of the effective acceptor concentration. As a consequence, both the ohmic contact characteristics and the semiconductor sheet resistance are worsened.     

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.     

Effects of vacuum annealing on electrical properties of GaN contacts

To understand formation and deterioration mechanisms of Ta/Ti ohmic contacts that were previously developed for p-GaN, the electrical properties of the Ta/Ti contacts, which were deposited on undoped GaN substrates and subsequently annealed in vacuum (where a slash (/) sign indicates the deposition sequence), were studied. The Ta/Ti contacts displayed good ohmic behavior after annealing at a temperature of 800°C for 10 min in vacuum, although the undoped GaN substrates were used. However, deterioration of the present ohmic contacts was observed during room-temperature storage. These contact properties were similar to those observed in the Ta/Ti contacts prepared on p-GaN. Hall-effect measurements revealed that thin n-type conductive layers were found to form on surfaces of both the undoped GaN and p-GaN substrates after annealing at 800°C in vacuum.