p型GaN器件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方面的应用潜能而被广为研究.低阻欧姆接触是提高GaN基器件光电性能的关键.由于低掺杂和空穴电离等原因,p-GaN上的低阻接触难于制备.制备稳定的P-GaN欧姆接触一直是一个挑战.主要通过对有关英语期刊文献的归纳分析,介绍了近年来在改进P-GaN工艺、提高欧姆接触性能等方面的研究进展.     

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.     

高亮度GaN基蓝色LED的研究进展

超高亮度GaN基蓝色LED的发展将会引起照明技术的一场革命，它是目前全球半导体领域研究和投资的特点。本文综合分析了GaN材料的特性及相应的材料生长和欧姆接触、刻蚀工艺等关键技术，并对GaN基蓝色LED器件的进一步改进及应用前景作了展望。     

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.     

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.     

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.     

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.     

低电阻GaN基太赫兹空气桥结构平面肖特基二极管

提出了通过增大欧姆接触电极包围角提高GaN基太赫兹肖特基二极管的截止频率的方法,该方法减小了空气桥结构平面肖特基二极管的串联电阻,进而提高了器件的截止频率.设计并制备了不同欧姆接触电极包围角的空气桥结构平面肖特基二极管,通过对器件Ⅰ-Ⅴ特性及C-V特性的测量,可知随着欧姆接触电极包围角的增大,肖特基二极管的串联电阻减小,而肖特基二极管的总电容并没有受影响.欧姆接触电极全包围结构的肖特基二极管截止频率为264 GHz,约为欧姆接触电极包围角为180°器件的1.6倍.     

p型GaN基器件的欧姆接触

宽带隙的GaN具有优良的物理和化学性质,己成为半导体领域研究的热点之一。p型GaN的欧姆接触问题制约了GaN基器件的进-步发展。本文首先介绍了欧姆接触的原理及评价方法,详细讨论了实现良好的p型GaN欧姆接触的主要方法是采取表面处理技术、选择合适的金属电极材料和进行热退火处理,以及研究进展情况。最后指出目前存在的问题并提出今后的研究方向。     

GaN基HFET电力电子器件的研究

作为第三代宽禁带半导体器件,GaN基HFET功率器件具耐高压、高频、导通电阻小等优良特性,在电力电子器件方面也具有卓越的优势。概述了基于电力电子方面应用的AlGaN/GaN HFET功率器件的研究进展。从器件的结构入手,介绍了AlGaN/GaN HEMT的研究现状,从栅材料的选取以及栅介质层的结构对器件性能的影响着手,对AlGaN/GaN MIS-HFET的研究进行了详细的介绍。分析了场板改善器件击穿特性的原理以及各种场板结构AlGaN/GaNHFET器件的研究进展。论述了实现增强型器件不同的方法。阐述了GaN基HFET功率器件在材料、器件结构、稳定性、工艺等方面所面临的挑战。最后探讨了GaN基HFET功率器件未来的发展趋势。     

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.     

High resolution physical analysis of ohmic contact formation at GaN-HEMT devices

A low ohmic contact resistance is a key request on AlGaN/GaN HEMT devices especially when dealing with higher frequency applications. In such a GaN material system very high annealing temperatures of up to 900 °C are frequently necessary to achieve low ohmic resistance. It is known that high annealing temperatures could reduce electrical performance and reliability of the devices. Therefore, low contact resistances at reduced annealing temperatures are beneficial. In the present work a special SiCl₄ plasma treatment was applied prior to the ohm metallisation resulting in sufficiently low ohmic resistances at a significantly reduced anneal temperature of 750 °C. High resolution physical analysis by transmission electron microscopy (TEM) and time of flight secondary mass spectroscopy (TOFSIMS) have been performed to understand the structural and chemical differences between the treated ohmic contacts compared to contacts processed under standard conditions. An advanced preparation technique was developed to get access to the reaction interfaces for TOFSIMS analysis from backside. It could be shown that the SiCl₄ treated samples reveal less impurities/contaminants on the ohmic metal–GaN/AlGaN interface and a different metal semiconductor alloying. The diffusion of metals like Al and Au into the semiconductor substrate was detected at the front of the TiN forming reaction.     

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.     

超薄势垒InAlN/GaN HFET器件高频特性分析

采用二次外延重掺杂n+ GaN实现非合金欧姆接触,并通过优化干法刻蚀和金属有机化学气相沉积(MOCVD)外延工艺,有效降低了欧姆接触电阻.将非合金欧姆接触工艺应用于InAlN/GaN异质结场效应晶体管(HFET)器件制备,器件的有效源漏间距缩小至600 nm.同时,结合40 nm T型栅工艺,制备了高电流截止频率(fT)和最大振荡频率(fmax)的InAlN/GaN HFET器件.结果显示减小欧姆接触电阻和栅长后,器件的电学特性,尤其是射频特性得到大幅提升.栅偏压为0V时,器件最大漏源饱和电流密度达到1.88 A/mm;直流峰值跨导达到681 mS/mm.根据射频小信号测试结果外推得到器件的fT和fmax同为217 GHz.     

Effect of annealing temperature on Ti/Al/Ni/Au ohmic contacts on undoped AlN films

The Ti/Al/Ni/Au metals were deposited on undoped AlN films by electron beam evaporation. The influence of annealing temperature on the properties of contacts was investigated. When the annealing temperatures were between 800 and 950℃, the AlN-Ti/Al/Ni/Au contacts became ohmic contacts and the resistance decreased with the increase of annealing temperature. A lowest specific contacts resistance of 0.379 Ω·cm² was obtained for the sample annealed at 950℃. In this work, we confirmed that the formation mechanism of ohmic contacts on AlN was due to the formation of Al-Au, Au-Ti and Al-Ni alloys, and reduction of the specific contacts resistance could originate from the formation of Au₂Ti and AlAu₂ alloys. This result provided a possibility for the preparation of AlN-based high-frequency, high-power devices and deep ultraviolet devices.     

Optimization of AuGe-Ni-Au ohmic contacts for GaAs MOSFETs

GaAs-based metal-oxide-semiconductor field-effect transistors (MOSFETs) are promising devices for high-speed and high-power applications. One important factor influencing the performance of a GaAs MOSFET is the characteristics of ohmic contacts at the drain and source terminals. In this paper, AuGe-Ni-Au metal contacts fabricated on a thin (930 /spl Aring/) and lightly doped (4/spl times/10/sup 17/ cm/sup -3/) n-type GaAs MOSFET channel layer were studied. The effects of controllable processing factors such as the AuGe thickness, the Ni/AuGe thickness ratio, alloy temperature, and alloy time to the characteristics of the ohmic contacts were analyzed. Contact qualities including specific contact resistance, contact uniformity, and surface morphology were optimized by controlling these processing factors. Using the optimized process conditions, a specific contact resistance of 5.6/spl times/10/sup -6/ /spl Omega//spl middot/cm/sup 2/ was achieved. The deviation of contact resistance and surface roughness were improved to 1.5% and 84 /spl Aring/, respectively. Using the improved ohmic contacts, high-performance GaAs MOSFETs (2 /spl mu/m/spl times/100 /spl mu/m) with a large drain current density (350 mA/mm) and a high transconductance (90 mS/mm) were fabricated.     

Metal contacts to gallium arsenide

In this paper, some aspects that determine the properties of Schottky and ohmic contacts to GaAs are discussed. For Schottky barrier diodes (SBD), we present results of a comprehensive study involving 41 different metals. We pay special attention to Ru and show that its thermal and chemical stability makes it ideal for use in devices operating above room temperature and for experiments involving annealing. Further, we discuss the effect of different metallization methods on SBD properties and show that methods which use energetic particles, such as electron beam deposition and sputter deposition, often result in inferior SBD properties—the consequence of electrically active defects introduced by the energetic particles at and close to the semiconductor surface. The advantages of using Ru as contact material to GaAs are that it forms high quality, thermally stable Schottky contacts to n-GaAs and thermally stable ohmic contacts with low specific contact resistance to p-GaAs. The versatile applicability of Ru contacts makes them extremely important for future use in devices such as heterojunction bipolar transistors and solid state lasers.