Degradation Mechanism of Pd/p-GaN Ohmic Contacts

{ "defaultlang": "zh", "titlegroup": { "articletitle": [ { "lang": "zh", "data": [ { "name": "text", "data": "Pd/p-GaN欧姆接触退化机理" } ] }, { "lang": "en", "data": [ { "name": "text", "data": "Degradation Mechanism of Pd/p-GaN Ohmic Contacts" } ] } ] }, "contribgroup": { "author": [ { "name": [ { "lang": "zh", "surname": "张", "givenname": "帆", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "ZHANG", "givenname": "Fan", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff1", "text": "1" }, { "rid": "aff2", "text": "2" } ], "role": [ "first-author" ], "bio": [ { "lang": "zh", "text": [ "张帆(1994-)，男，山西太原人，硕士研究生，2017年于中北大学获得学士学位，主要从事GaN半导体蓝绿光激光器的研究。E-mail: fzhang2019@sinano.ac.cn" ], "graphic": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352524&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352528&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352532&type=" } ], "data": [ [ { "name": "text", "data": "张帆" }, { "name": "text", "data": "(1994-)，男，山西太原人，硕士研究生，2017年于中北大学获得学士学位，主要从事GaN半导体蓝绿光激光器的研究。E-mail: " }, { "name": "text", "data": "fzhang2019@sinano.ac.cn" } ] ] } ], "email": "fzhang2019@sinano.ac.cn", "deceased": false }, { "name": [ { "lang": "zh", "surname": "王", "givenname": "荣新", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "WANG", "givenname": "Rong-xin", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff3", "text": "3" } ], "role": [ "corresp" ], "corresp": [ { "rid": "cor3", "lang": "en", "text": "* Corresponding Author, E-mail: rxwang2008@sinano.ac.cn", "data": [ { "name": "text", "data": "* Corresponding Author, E-mail: rxwang2008@sinano.ac.cn" } ] } ], "bio": [ { "lang": "zh", "text": [ "王荣新(1963-)，女，河北石家庄人，博士，正高级工程师，2005年于中国香港大学获得博士学位，主要从事微纳加工工艺、半导体器件的制备和表征研究。E-mail:rxwang2008@sinano.ac.cn" ], "graphic": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352536&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352540&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352545&type=" } ], "data": [ [ { "name": "text", "data": "王荣新" }, { "name": "text", "data": "(1963-)，女，河北石家庄人，博士，正高级工程师，2005年于中国香港大学获得博士学位，主要从事微纳加工工艺、半导体器件的制备和表征研究。E-mail:" }, { "name": "text", "data": "rxwang2008@sinano.ac.cn" } ] ] } ], "email": "rxwang2008@sinano.ac.cn", "deceased": false }, { "name": [ { "lang": "zh", "surname": "黄", "givenname": "思溢", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "HUANG", "givenname": "Si-yi", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff1", "text": "1" } ], "role": [], "deceased": false }, { "name": [ { "lang": "zh", "surname": "田", "givenname": "爱琴", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "TIAN", "givenname": "Ai-qin", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff1", "text": "1" } ], "role": [], "deceased": false }, { "name": [ { "lang": "zh", "surname": "刘", "givenname": "建平", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "LIU", "givenname": "Jian-ping", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff1", "text": "1" } ], "role": [], "deceased": false }, { "name": [ { "lang": "zh", "surname": "杨", "givenname": "辉", "namestyle": "eastern", "prefix": "" }, { "lang": "en", "surname": "YANG", "givenname": "Hui", "namestyle": "eastern", "prefix": "" } ], "stringName": [], "aff": [ { "rid": "aff1", "text": "1" }, { "rid": "aff2", "text": "2" } ], "role": [ "corresp" ], "corresp": [ { "rid": "cor4", "lang": "en", "text": "hyang2006@sinano.ac.cn", "data": [ { "name": "text", "data": "hyang2006@sinano.ac.cn" } ] } ], "bio": [ { "lang": "zh", "text": [ "杨辉(1961-)，男，天津人，博士，研究员，1991年于中国科学院半导体研究所获得博士学位，主要从事Ⅲ-Ⅴ族化合物半导体的材料生长、物理分析及器件的研究。E-mail:hyang2006@sinano.ac.cn" ], "graphic": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352548&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352552&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352555&type=" } ], "data": [ [ { "name": "text", "data": "杨辉" }, { "name": "text", "data": "(1961-)，男，天津人，博士，研究员，1991年于中国科学院半导体研究所获得博士学位，主要从事Ⅲ-Ⅴ族化合物半导体的材料生长、物理分析及器件的研究。E-mail:" }, { "name": "text", "data": "hyang2006@sinano.ac.cn" } ] ] } ], "email": "hyang2006@sinano.ac.cn", "deceased": false } ], "aff": [ { "id": "aff1", "intro": [ { "lang": "zh", "label": "1", "text": "中国科学院苏州纳米技术与纳米仿生研究所　纳米器件与相关材料研究部，江苏 　 苏州 　 215123", "data": [ { "name": "text", "data": "中国科学院苏州纳米技术与纳米仿生研究所　纳米器件与相关材料研究部，江苏 　 苏州 　 215123" } ] }, { "lang": "en", "label": "1", "text": "Key Laboratory of Nano-devices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China", "data": [ { "name": "text", "data": "Key Laboratory of Nano-devices and Applications, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China" } ] } ] }, { "id": "aff2", "intro": [ { "lang": "zh", "label": "2", "text": "上海科技大学　物质科学与技术学院，上海 　 201210", "data": [ { "name": "text", "data": "上海科技大学　物质科学与技术学院，上海 　 201210" } ] }, { "lang": "en", "label": "2", "text": "School of Physical Science and Technology, Shanghai Tech University, ShangHai 201210, China", "data": [ { "name": "text", "data": "School of Physical Science and Technology, Shanghai Tech University, ShangHai 201210, China" } ] } ] }, { "id": "aff3", "intro": [ { "lang": "zh", "label": "3", "text": "中国科学院苏州纳米技术与纳米仿生研究所　纳米真空互联实验平台，江苏 　 苏州 　 215123", "data": [ { "name": "text", "data": "中国科学院苏州纳米技术与纳米仿生研究所　纳米真空互联实验平台，江苏 　 苏州 　 215123" } ] }, { "lang": "en", "label": "3", "text": "Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China", "data": [ { "name": "text", "data": "Vacuum Interconnected Nanotech Workstation, Suzhou Institute of Nano-Tech and Nano-Bionics, Chinese Academy of Sciences, Suzhou 215123, China" } ] } ] } ] }, "abstracts": [ { "lang": "zh", "data": [ { "name": "p", "data": [ { "name": "text", "data": "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。" } ] } ] }, { "lang": "en", "data": [ { "name": "p", "data": [ { "name": "text", "data": "GaN-based wide bandgap semiconductors and devices have been quickly emerging as a new frontier and cutting-edge technique. It is necessary to fabricate Ohmic contact for GaN device application. Pd is one of candidate metals for fabricating metal/p-GaN Ohmic contacts. Under the identical preparation conditions, different thickness Pd films were sputtered on p-GaN epilayers in sputtering chamber directly connected with MOCVD growth system. After the metal deposition, the samples were then annealed at 300 ℃ and 600 ℃ in ambient atmosphere of N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1 or under vacuum conditions for 90 s. They were measured and characterized by four-probe Van de Pauw, X-ray photoelectron spectroscopy(XPS), and atomic force microscopy(AFM). It is found that the electrical properties and surface morphologies of samples were dependent on annealing ambient atmosphere and heat treatment temperature conditions. When the samples were annealed at 600 ℃ under high vacuum conditions, Ga can be diffused out from Pd/p-GaN interface. It would be helpful to make Ga and Pd reactive to become alloy as well as to produce Ga vacancy for Ohmic contact. While the samples were annealed in N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1 environment, however, oxidation of metal Pd and Ga becomes a dominant factor resulting in degradation of the Ohmic contacts.The higher the annealing temperature in oxygen environment, the worse the electrical properties. Surface morphologies of the annealed samples were completely changed from a smooth atomic step morphology to a dendritic polycrystal grain state if oxygen was participated into the interface during the annealing process. Therefore, avoiding oxygen incorporation at Pd/p-GaN interface shall be a key role in forming alloy and Ohmic contact, which favors the stability and reliability of device performance." } ] } ] } ], "keyword": [ { "lang": "zh", "data": [ [ { "name": "text", "data": "p型GaN" } ], [ { "name": "text", "data": "欧姆接触" } ], [ { "name": "text", "data": "XPS" } ], [ { "name": "text", "data": "界面" } ] ] }, { "lang": "en", "data": [ [ { "name": "text", "data": "p-GaN" } ], [ { "name": "text", "data": "Ohmic contact" } ], [ { "name": "text", "data": "XPS" } ], [ { "name": "text", "data": "interface" } ] ] } ], "highlights": [], "body": [ { "name": "sec", "data": [ { "name": "sectitle", "data": { "title": [ { "name": "text", "data": "1　引言" } ], "level": "1", "id": "s1" } }, { "name": "p", "data": [ { "name": "text", "data": "在过去的十几年中，GaN和SiC等第三代半导体材料由于具有宽直接带隙、稳定的化学性质、良好的抗辐照能力和高临界电场等特性，其材料生长和器件制造发展迅速。特别是近年来，GaN在高温、高频中的广泛应用倍受关注" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "1", "type": "bibr", "rid": "R1", "data": [ { "name": "text", "data": "1" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "5", "type": "bibr", "rid": "R5", "data": [ { "name": "text", "data": "5" } ] } } ], "rid": [ "R1", "R2", "R3", "R4", "R5" ], "text": "1-5", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。2014年，获诺贝尔物理学奖的Shuji Nakamura预言GaN基材料与器件的发展正在步入一个快车道。因此，一个以GaN为基础衬底的庞大规模的光电子和电子产业浪潮正在加速形成。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "无论电子器件(大功率晶体管" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "3", "type": "bibr", "rid": "R3", "data": [ { "name": "text", "data": "3" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": ")还是光电器件(LEDs" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "4", "type": "bibr", "rid": "R4", "data": [ { "name": "text", "data": "4" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，激光器" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "5", "type": "bibr", "rid": "R5", "data": [ { "name": "text", "data": "5" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": ")均离不开接触电极的制备，利用金属材料制备接触电极是实现器件功能必需的结构。金属与半导体接触后将产生金半接触势垒，势垒的高度决定着电流电压特性为欧姆接触或是肖特基接触" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "6", "type": "bibr", "rid": "R6", "data": [ { "name": "text", "data": "6" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，也是制约器件性能的主要因素之一。因此，电极材料的选择与制备以及高温、高频、大功率下器件性能的稳定就显得尤为重要。一般来说，n型材料和p型材料制备欧姆接触选择的金属有所不同，在n-GaN制备欧姆接触常用低功函数的金属Ti、Al等" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "7", "type": "bibr", "rid": "R7", "data": [ { "name": "text", "data": "7" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "9", "type": "bibr", "rid": "R9", "data": [ { "name": "text", "data": "9" } ] } } ], "rid": [ "R7", "R8", "R9" ], "text": "7-9", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": ",p-GaN则选用高功函数的金属Pd、Pt、Au、Ni等" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "10", "type": "bibr", "rid": "R10", "data": [ { "name": "text", "data": "10" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "11", "type": "bibr", "rid": "R11", "data": [ { "name": "text", "data": "11" } ] } } ], "rid": [ "R10", "R11" ], "text": "10-11", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。在正面出光的LED中常用Ni/Au作为透明接触金属，然而对于激光器等在高电流密度和大功率下工作的器件而言，Ni/Au作为接触金属时，在工作一段时间后，往往出现工作电压升高、器件性能严重退化等问题。而使用金属Pd作为接触金属则能够有效地防止器件性能退化，获得良好的电压稳定性和可靠性" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "12", "type": "bibr", "rid": "R12", "data": [ { "name": "text", "data": "12" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "13", "type": "bibr", "rid": "R13", "data": [ { "name": "text", "data": "13" } ] } } ], "rid": [ "R12", "R13" ], "text": "12-13", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。目前，选用5.12 eV功函数的Pd制备出的p-GaN欧姆接触依然存在接触电阻偏大、器件稳定性低、长时间工作串联电阻值不断增加等诸多问题，需要进行深入研究。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "GaN的Ga极性表面对于氧原子的化学吸附非常活跃，导致在表面上产生天然氧化物" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "14", "type": "bibr", "rid": "R14", "data": [ { "name": "text", "data": "14" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。表面氧化物会产生一个势垒，阻碍载流子从金属向半导体的传输，增加了欧姆接触的电阻值。因此，在金属Pd沉积之前去除氧化物可以有效地降低接触电阻率" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "15", "type": "bibr", "rid": "R15", "data": [ { "name": "text", "data": "15" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。目前制备金属接触经常利用H" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "SO" }, { "name": "sub", "data": [ { "name": "text", "data": "4" } ] }, { "name": "text", "data": "、HCl、NH" }, { "name": "sub", "data": [ { "name": "text", "data": "3" } ] }, { "name": "text", "data": "·H" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "O、KOH和王水等化学清洗的办法除去GaN表面的氧化物和表面沾污，之后沉积金属材料，再高温退火形成欧姆接触。然而，人为前期清洗处理会造成GaN样品表面状态的不可控，呈现出表面缺陷、费米能级钉扎等不理想因素。特别是对本身极性的p-GaN而言，既需要利用高温有氧环境打断Mg—H键实现Mg杂质激活" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "16", "type": "bibr", "rid": "R16", "data": [ { "name": "text", "data": "16" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "17", "type": "bibr", "rid": "R17", "data": [ { "name": "text", "data": "17" } ] } } ], "rid": [ "R16", "R17" ], "text": "16-17", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，又存在着极性GaN材料表面非常容易吸附杂质而形成表面缺陷态，甚至形成氧化层的可能，如此不仅改变了金半接触的势垒高度，而且金半界面氧的存在也将促使器件稳定性变差导致性能退化等问题。例如，在器件制备工艺中金属Pd和p-GaN形成欧姆接触时，退火气氛通常选用氧环境，使得H与O结合进一步激活Mg，提升欧姆接触性能，期间发生氧化是不可避免的。在高温退火过程中，特别是有氧高温环境下，一方面氧会扩散进入器件内部成为缺陷释放/捕获电子影响载流子输运;另一方面，电极金属和Ga(GaN)形成合金" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "15", "type": "bibr", "rid": "R15", "data": [ { "name": "text", "data": "15" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "获得欧姆接触" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "18", "type": "bibr", "rid": "R18", "data": [ { "name": "text", "data": "18" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "21", "type": "bibr", "rid": "R21", "data": [ { "name": "text", "data": "21" } ] } } ], "rid": [ "R18", "R19", "R20", "R21" ], "text": "18-21", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，期间也将出现互扩散、化学反应(Ga、Pd等氧化)等现象。有文献报道，氧与金属Pd在高温下反应成为PdO" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "blockXref", "data": { "data": [ { "name": "xref", "data": { "text": "22", "type": "bibr", "rid": "R22", "data": [ { "name": "text", "data": "22" } ] } }, { "name": "text", "data": "-" }, { "name": "xref", "data": { "text": "23", "type": "bibr", "rid": "R23", "data": [ { "name": "text", "data": "23" } ] } } ], "rid": [ "R22", "R23" ], "text": "22-23", "type": "bibr" } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，电阻升高" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "24", "type": "bibr", "rid": "R24", "data": [ { "name": "text", "data": "24" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。如此异常复杂的Pd和GaN界面状态及其变化等导致对载流子传输的机理尚不十分清楚，甚少有人涉足，尤其金属与半导体接触界面化学状态变化对器件性能退化影响的研究有待加强。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "本文借助真空互联系统(真空度" }, { "name": "text", "data": "<" }, { "name": "text", "data": "4.0×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-8" } ] }, { "name": "text", "data": " Pa(3×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-10" } ] }, { "name": "text", "data": " torr))，将生长GaN的MOCVD设备通过氮气手套箱与工艺设备、表面分析设备利用真空管道连接在一起，有效地控制了样品表面状态，重点研究了不同环境、温度等退火条件下金属Pd与GaN表界面微观结构、组分、化学状态等演变情况，发现有氧高温下Pd极易氧化，Pd的氧化导致电阻升高，电学性能随之恶化，进而导致器件性能下降。本工作揭示了Pd/P-GaN高温条件的微观结构以及金属覆盖层的结构演变，对于高功率和高温下GaN器件的实际应用具有极其重要的意义。" } ] } ] }, { "name": "sec", "data": [ { "name": "sectitle", "data": { "title": [ { "name": "text", "data": "2　实验" } ], "level": "1", "id": "s2" } }, { "name": "p", "data": [ { "name": "text", "data": "使用德国Aixtron公司生产的近耦合喷淋头型设备(Close coupled showerhead，简称 CCS)、采用金属有机化学气相沉积(MOCVD)法生长样品，在蓝宝石(0001)衬底上分别生长了4 μm的n-GaN、500 nm的p-GaN、掺Mg浓度为1×10" }, { "name": "sup", "data": [ { "name": "text", "data": "20" } ] }, { "name": "text", "data": " cm" }, { "name": "sup", "data": [ { "name": "text", "data": "-3" } ] }, { "name": "text", "data": " 20 nm厚的p" }, { "name": "sup", "data": [ { "name": "text", "data": "++" } ] }, { "name": "text", "data": "-GaN膜，结构如" }, { "name": "xref", "data": { "text": "图1", "type": "fig", "rid": "F1", "data": [ { "name": "text", "data": "图1" } ] } }, { "name": "text", "data": "所示。生长完成之后，通过氮气手套箱及超高真空(UHV)(真空度" }, { "name": "text", "data": "<" }, { "name": "text", "data": "1.3×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-8" } ] }, { "name": "text", "data": " Pa(10" }, { "name": "sup", "data": [ { "name": "text", "data": "-10" } ] }, { "name": "text", "data": " torr))管道传送至磁控溅射设备(Sputter，本底真空" }, { "name": "text", "data": "<" }, { "name": "text", "data": "6.7×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-7" } ] }, { "name": "text", "data": " Pa(5×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-9" } ] }, { "name": "text", "data": " torr))，在不加热基底的情况下溅射2,4,6,8 nm等不同厚度的金属Pd，之后样品通过管道传送至快速退火炉内，分别在不同气氛(N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1和真空" }, { "name": "text", "data": "<" }, { "name": "text", "data": "6.7×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-7" } ] }, { "name": "text", "data": " Pa(5×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-9" } ] }, { "name": "text", "data": " torr))下进行时间为90 s、温度为573 K和873 K的退火处理。生长p-GaN表面的原始信息和Pd/GaN界面的元素组成及元素价态变化使用单色Al Kα(1 486.7 eV)型号为PHI5000X射线光电子能谱(XPS)进行监测，在测试0~3 000 eV宽谱扫描后，针对关注的碳、氧、钯、镓和氮等元素进一步精选检测，通过旋转不同角度获得样品深度变化的信息，借助成熟的标准商用CasaXPS软件分析了对应的测试谱图，得到样品退火前后化学状态的变化情况。利用Napson CRESBOX半自动四探针测试仪测试样品薄膜电阻特性。样品表面形貌使用OXFORD公司的Asylum Research MFP-3D原子力显微镜(AFM)进行测试表征。" } ] }, { "name": "fig", "data": { "id": "F1", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图1" } ], "title": [ { "name": "text", "data": "p型GaN样品结构图" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.1" } ], "title": [ { "name": "text", "data": "Structure diagram of p-type GaN sample" } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352558&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352565&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352561&type=" } ] } } ] }, { "name": "sec", "data": [ { "name": "sectitle", "data": { "title": [ { "name": "text", "data": "3　结果与讨论" } ], "level": "1", "id": "s3" } }, { "name": "p", "data": [ { "name": "xref", "data": { "text": "图2", "type": "fig", "rid": "F2", "data": [ { "name": "text", "data": "图2" } ] } }, { "name": "text", "data": "给出了在p-GaN样品上溅射不同厚度金属Pd、不同退火温度以及不同退火气氛下电阻率的变化，从图中可以发现一定的规律性。对于未退火样品来说，随着金属厚度增加，Pd薄膜的电阻率降低，即Pd薄膜的电阻率从2 nm的7.7×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-5" } ] }, { "name": "text", "data": " Ω·cm降低至8 nm的2.4×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-5" } ] }, { "name": "text", "data": " Ω·cm，也就是说，Pd薄膜厚度越厚越接近于1.08×10" }, { "name": "sup", "data": [ { "name": "text", "data": "-5" } ] }, { "name": "text", "data": " Ω·cm Pd体材料的电阻率。对于真空环境下退火样品而言，与未退火样品的电阻率数值及变化趋向十分相近;对于N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛环境下退火样品呈现出随着退火温度升高，电阻率发生明显升高的趋势。在GaN衬底上沉积单一金属材料，影响其电阻率的主要因素包括金属薄膜厚度、薄膜均匀性、表面状态、薄膜微结构、界面效应、化学状态变化等。为探究其中的原因，我们分别对样品进行了AFM和XPS测试。" } ] }, { "name": "fig", "data": { "id": "F2", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图2" } ], "title": [ { "name": "text", "data": "沉积不同溅射金属厚度和不同退火条件下样品的电阻率" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.2" } ], "title": [ { "name": "text", "data": "Variation of the resistivity of the sample as-deposited and annealed at different conditions" } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352569&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352577&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352573&type=" } ] } }, { "name": "p", "data": [ { "name": "text", "data": "首先对未退火的情况进行分析，" }, { "name": "xref", "data": { "text": "图3(a)~(d)", "type": "fig", "rid": "F3", "data": [ { "name": "text", "data": "图3(a)~(d)" } ] } }, { "name": "text", "data": "给出了MOCVD生长的p-GaN表面、沉积2 nm Pd薄膜AFM测试图像以及不同角度下测试Ga3d核心能级的XPS测试曲线，从AFM测试图像中观察到无论是p-GaN还是GaN上沉积不同厚度(2,4,6,8 nm)Pd的样品表面均呈现明显的外延生长原子台阶形貌(未全部给出AFM测试图像)，表明沉积的Pd薄膜表面平整且均匀一致。" }, { "name": "xref", "data": { "text": "图3(a)", "type": "fig", "rid": "F3", "data": [ { "name": "text", "data": "图3(a)" } ] } }, { "name": "text", "data": "中p-GaN样品上XPS测试的Ga3d峰主要的自于Ga—N、Ga—O、Ga—Ga和N2s等4种成键结合能峰" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "25", "type": "bibr", "rid": "R25", "data": [ { "name": "text", "data": "25" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，通过分析各个峰面积比例关系可以发现GaN样品表面上C、O元素含量很低，即Ga—O键所占比例很低，表明p-GaN表面Ga的氧化程度极低，为形成良好的欧姆接触提供了极为有利的前提条件。从" }, { "name": "xref", "data": { "text": "图3(c)", "type": "fig", "rid": "F3", "data": [ { "name": "text", "data": "图3(c)" } ] } }, { "name": "text", "data": "典型的Pd(2 nm)/p-GaN样品变角度XPS测试的Ga3d峰可以观察到，随着测试发射角" }, { "name": "italic", "data": [ { "name": "text", "data": "θ" } ] }, { "name": "text", "data": "的增大，Pd(2 nm)/p-GaN中的Ga3d峰向较高能量偏移。实际上，XPS测试时电子逸出深度取决于材料中元素的结合能，与测试发射角(" }, { "name": "italic", "data": [ { "name": "text", "data": "θ" } ] }, { "name": "text", "data": ")的关系为" }, { "name": "italic", "data": [ { "name": "text", "data": "λ" } ] }, { "name": "text", "data": "sin" }, { "name": "italic", "data": [ { "name": "text", "data": "θ" } ] }, { "name": "text", "data": "，其中" }, { "name": "italic", "data": [ { "name": "text", "data": "λ" } ] }, { "name": "text", "data": "是电子的非弹性平均自由程。根据NIST数据库" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "26", "type": "bibr", "rid": "R26", "data": [ { "name": "text", "data": "26" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "中的TPP-2M方法" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "27", "type": "bibr", "rid": "R27", "data": [ { "name": "text", "data": "27" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "计算，GaN中Ga3d的电子的" }, { "name": "italic", "data": [ { "name": "text", "data": "λ" } ] }, { "name": "text", "data": "值为2.6 nm。" }, { "name": "xref", "data": { "text": "图3(d)", "type": "fig", "rid": "F3", "data": [ { "name": "text", "data": "图3(d)" } ] } }, { "name": "text", "data": "显示出Ga3d峰的结合能随检测深度(大约3" }, { "name": "italic", "data": [ { "name": "text", "data": "λ" } ] }, { "name": "text", "data": ")的变化趋势，这意味着GaN表面层中存在明显的能带弯曲现象，越接近Pd(2 nm)/p-GaN界面区域结合能越低。由于Ga—Ga金属键" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "25", "type": "bibr", "rid": "R25", "data": [ { "name": "text", "data": "25" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "和Ga—Pd金属键" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "28", "type": "bibr", "rid": "R28", "data": [ { "name": "text", "data": "28" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "结合能的范围均在15~20 eV区间，说明金属键(Ga—Ga或Ga—Pd)成分增大。我们知道，在溅射过程中，主要是利用电场离化气体，产生等离子体，轰击靶材，从靶材上脱离的高能粒子到达样品表面、吸附并沉积成为薄膜。在Pd沉积GaN衬底的初期，Pd到达GaN的表面，与GaN表面的Ga结合易形成Pd—Ga结合键，产生Pd" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "x" } ] } ] }, { "name": "text", "data": "Ga" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "y" } ] } ] }, { "name": "text", "data": "合金态" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "29", "type": "bibr", "rid": "R29", "data": [ { "name": "text", "data": "29" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，与上述XPS测试结果十分吻合，即Ga—Pd金属键成分增大Ga3d峰向低结合能方向偏移。随着Pd原子的不断到来，GaN表面被完全覆盖，Pd—Pd逐渐增多，薄膜厚度增厚，Pd" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "x" } ] } ] }, { "name": "text", "data": "Ga" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "y" } ] } ] }, { "name": "text", "data": "合金态的比例在沉积的Pd薄膜中的份额越来越低，因此，电阻率的数值表现出上述情况。随着金属厚度增加，Pd薄膜的电阻率降低，更趋向于Pd体材料的电阻率。下文还将详细分析Pd" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "x" } ] } ] }, { "name": "text", "data": "Ga" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "y" } ] } ] }, { "name": "text", "data": "对薄膜电阻率的影响。" } ] }, { "name": "fig", "data": { "id": "F3", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图3" } ], "title": [ { "name": "text", "data": "(a)p-GaN表面Ga3d核心能级的原始信息;(b)为p-GaN表面AFM表面形貌;(c)2 nm Pd/p-GaN样品的Ga3d核心能谱(插图显示了Ga3d(Ga—N)峰的结合能随检测深度的变化);(d)2 nm Pd/p-GaN表面AFM表面形貌。" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.3" } ], "title": [ { "name": "text", "data": "(a)High-resolution XPS spectra of Ga3d core energy level on p-GaN surface. (b)AFM surface morphology of p-GaN surface. (c)Ga3d core energy spectra of 2 nm Pd/p-GaN sample(inset shows the binding energy of Ga3d(Ga—N) peak changes with the detection depth). (d)AFM surface morphology of 2 nm Pd/p-GaN surface." } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352581&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352589&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352585&type=" } ] } }, { "name": "p", "data": [ { "name": "text", "data": "接着讨论退火处理对电阻率的影响。由于573 K是金属Pd与GaN刚开始发生反应的温度，而873 K是在金属Pd/Pt/Au与GaN形成良好欧姆接触的最佳温度，因此选取这两个关键温度作为研究比较。对于退火样品，从" }, { "name": "xref", "data": { "text": "图2", "type": "fig", "rid": "F2", "data": [ { "name": "text", "data": "图2" } ] } }, { "name": "text", "data": "中同样可以发现随着金属厚度增加而Pd薄膜电阻率减低的规律。在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1的气氛下，当金属厚度保持不变时，随着退火温度升高，电阻率出现先有所下降、再迅速升高的趋势，溅射2,4,6,8 nm金属Pd的样品的电阻率都呈现相同的趋势。此外，与未退火的样品相比，退火后多数Pd薄膜的电阻率数值略显减低。退火处理对薄膜电阻率和Pd与p-GaN界面的影响有可能来自两个方面:(1) 高温下原子能获得足够的能量而移动，这有利于消除薄膜的缺陷，提高薄膜的致密度，改变薄膜的电阻率;(2)出现互扩散、化学价态和化学状态等变化，如合金、氧化等改变薄膜电阻率。薄膜中合金态、氧化态对电特性的影响可以借助XPS进行分析了解。为此，利用XPS测试了不同退火温度的Pd/p-GaN样品。" }, { "name": "xref", "data": { "text": "图4(a)、(b)、(c)", "type": "fig", "rid": "F4", "data": [ { "name": "text", "data": "图4(a)、(b)、(c)" } ] } }, { "name": "text", "data": "给出了典型的Pd(4 nm)/p-GaN测试结果，从图中可以发现Ga3d、Pd3d和O1s峰位在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1的气氛下退火前后的变化趋势，样品的Ga3d峰位由未退火时的(19.3±0.1) eV移动到573 K退火后的(18.9±0.1) eV,Ga3d结合能降低说明除Ga—N键等外，金属键(Ga—Pd键或/和Ga—Ga键)结合能成分增大" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "25", "type": "bibr", "rid": "R25", "data": [ { "name": "text", "data": "25" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，或形成Ga—Pd合金相" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "30", "type": "bibr", "rid": "R30", "data": [ { "name": "text", "data": "30" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，或N脱离Ga—Ga结合加强。比较退火前后样品也观察到Pd3d5/2峰位从(335.5±0.1) eV向低结合能方向偏移到(335.2±0.1) eV的现象，证明金属原子之间结合键增强，薄膜内部空隙减少，结构更加紧凑，同时亦或Pd与Ga(p-GaN)发生反应，生成合金相，即退火有利于形成Ga—Pd合金相;同时我们还注意到峰型展宽，拟合半峰宽数值从1.19 eV增加到1.38 eV，高结合能端峰强明显增高，金属Pd可能与O反应发生了氧化，致使PdO成分增强。有文献报道，在531 K以上时Pd会氧化生成PdO" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "31", "type": "bibr", "rid": "R31", "data": [ { "name": "text", "data": "31" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，与我们的观察相吻合，证实了我们上述提出的影响因素来自两个方面的判断。一般情况下，观测氧化态还需与O1s共同分析，由于数据库显示O1s结合能是532 eV,Pd3p结合能是531 eV，二者峰位近乎完全重叠，无法分辨。" }, { "name": "xref", "data": { "text": "图4(c)", "type": "fig", "rid": "F4", "data": [ { "name": "text", "data": "图4(c)" } ] } }, { "name": "text", "data": "显示了在573 K退火温度获得结合能峰在526~544 eV区间的O1s/Pd3p能谱，Pd3p3/2的峰和O1s基本重合，极不易分辨清楚。对比未退火样品，依然可以发现Pd峰型略微展宽，通过拟合获得了Pd/PdO的比例关系，其数值从3.9减小到3.4，仅仅变化了13%。这也表明，当Pd/p-GaN样品在空气中较低温度(低于573 K)退火过程时，金属Pd既与Ga生成合金，又与O反应生成PdO，与未退火的样品电特性相比，阻值虽略有降低，但影响非常有限。" } ] }, { "name": "fig", "data": { "id": "F4", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图4" } ], "title": [ { "name": "text", "data": "4 nm Pd/p-GaN在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "气氛和超高真空不同退火温度下的XPS能谱。(a)Ga3d核心能级;(b)Pd3d5/2核心能级;(c)O1s/Pd3p核心能级。" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.4" } ], "title": [ { "name": "text", "data": "4 nm Pd/p-GaN as-deposited and annealed at different temperatures in N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": " atmosphere and ultra-high vacuum condition. (a)Ga3d core energy level. (b)Pd3d5/2 core energy level. (c)O1s/Pd3p core energy level." } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352593&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352601&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352597&type=" } ] } }, { "name": "p", "data": [ { "name": "text", "data": "为了深入了解和区分清楚上述提及的哪些是影响薄膜电特性的主导因素，在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1的气氛下，将退火温度进一步升高到873 K,Ga3d明显地分裂成为两个峰，其中高能量处呈现出Ga—O结合峰，结合能在(21.6±0.1) eV左右，低能量的峰则依然类似573 K退火情况，结合能在(18.9±0.1) eV左右，主要为Ga—N和Ga—Pd峰等。从" }, { "name": "xref", "data": { "text": "图4(c)", "type": "fig", "rid": "F4", "data": [ { "name": "text", "data": "图4(c)" } ] } }, { "name": "text", "data": "所示O1s/Pd3p结合能图谱中也清晰地观察到O1s和Pd3p分裂，展现出了(530.1±0.1) eV和(533.7±0.1) eV两个独立峰，低能端的530 eV 结合能峰为O1s，由O—Ga、O—Pd等组成" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "32", "type": "bibr", "rid": "R32", "data": [ { "name": "text", "data": "32" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，高能端534 eV结合能峰则反映出Pd3p的信息。此外，Pd3d峰同样显示出相应的变化趋势，不仅Pd3d5/2峰位明显从未退火时(335.5±0.1) eV偏移至(336.6±0.1) eV，而且Pd3d5/2峰型也由金属的非对称峰型转变成为非常明显的Pd的氧化态峰型，说明Pd发生了严重氧化，高温下Pd易发生氧化与文献报道一致" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "21", "type": "bibr", "rid": "R21", "data": [ { "name": "text", "data": "21" } ] } }, { "name": "text", "data": "," }, { "name": "xref", "data": { "text": "31", "type": "bibr", "rid": "R31", "data": [ { "name": "text", "data": "31" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。虽然理论上预计随着退火温度升高，金属Pd也将容易与Ga(p-GaN)发生反应生成合金相，但是由于峰型的变化和峰位的明显偏移，使得低能端Pd形成的合金态情况无法清晰地加以分辨。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "由于在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1的气氛下退火不仅造成薄膜材料氧化，还会出现互扩散、合金以及薄膜内部缺陷减少等并存状态的可能性。为了加以区别清楚，需避免氧气等气氛对电特性的影响，借助真空高温退火，研究其他因素的作用。在573 K退火时，与N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛下略微发生了合金和氧化不同，在真空条件下退火，表面形貌与未退火几乎没有变化，XPS分析Ga和Pd等元素没有明显的价态变化，对应结果不在这里展示。" }, { "name": "xref", "data": { "text": "图5", "type": "fig", "rid": "F5", "data": [ { "name": "text", "data": "图5" } ] } }, { "name": "text", "data": "给出了873 K真空退火后p-GaN上不同厚度Pd薄膜测试的XPS谱中Ga3d的变化情况，可以看到随着Pd厚度增加，Ga3d结合能依次减小，与未退火(19.2±0.1) eV相比，从2 nm Pd/p-GaN的(19.1±0.1) eV，移动至4 nm Pd/p-GaN的(19.0±0.1) eV，进一步降低至6 nm Pd/p-GaN的(18.8±0.1) eV。正如上文所述，Ga3d峰的结合能向低能端移动表明金属结合键成分加强，Pd3d5/2的峰同样表现出向更低的结合能方向移动，金属Pd与Ga合金化趋势明显。也就是说，873 K真空退火明显地增强合金化，有利于形成Ga-Pd合金相，Pd" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "x" } ] } ] }, { "name": "text", "data": "Ga" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "y" } ] } ] }, { "name": "text", "data": "合金总量增多。与相同厚度未退火样品的XPS测试数据比较，我们还发现可以获得更加清晰明确的Ga3d信息，表明GaN中的Ga原子在高温下从GaN表面向金属层中扩散，Ga的向外扩散在两个方面改变Pd/p-GaN的电流电压特性:(1)使得GaN表面Ga/N比例减小，有可能产生Ga空位，将有助于p-GaN的欧姆接触的实现" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "33", "type": "bibr", "rid": "R33", "data": [ { "name": "text", "data": "33" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": ";(2)Pd薄膜内Ga总量增多，促进Ga与Pd形成Ga-Pd合金的几率增大，Pd" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "x" } ] } ] }, { "name": "text", "data": "Ga" }, { "name": "sub", "data": [ { "name": "italic", "data": [ { "name": "text", "data": "y" } ] } ] }, { "name": "text", "data": "合金总含量更多。与未退火样品相比，随着厚度增加，真空退火后的样品出现电阻率相对降低的情况，而且下降趋势逐渐变缓慢，甚至产生电阻率略高的情况，表明与纯Pd薄膜相比，Ga-Pd合金的电阻率略微加大，导电机制发生变化。结合退火之后样品的电阻率以及Ga3d、Pd3d5/2、Pd3p和O1s能谱验证了真空退火与气氛退火的明显差异，即N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "气氛下退火温度越高金属Pd越容易被氧化，Ga和Pd氧化是导致薄膜电阻率急速升高的主导原因。薄膜电阻的显著增大将导致器件发热问题加剧，继而造成器件严重退化。" } ] }, { "name": "fig", "data": { "id": "F5", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图5" } ], "title": [ { "name": "text", "data": "不同厚度Pd在873 K退火真空气氛退火Ga3d核心能级" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.5" } ], "title": [ { "name": "text", "data": "High-resolution XPS Ga3d core energy level of different thickness Pd on GaN annealed at 873 K under vacuum condition" } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352605&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352612&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352608&type=" } ] } }, { "name": "p", "data": [ { "name": "text", "data": "Pd/p-GaN表面形貌和微结构同样与退火条件有关，" }, { "name": "xref", "data": { "text": "图6(a)~(d)", "type": "fig", "rid": "F6", "data": [ { "name": "text", "data": "图6(a)~(d)" } ] } }, { "name": "text", "data": "给出了4 nm Pd/p-GaN退火前后表面形貌的演变，在超高真空中873 K退火以及N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛中573 K退火的样品上观察到与未退火情况类似状况，基本保留了清晰的原子台阶形貌。在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛下，当退火温度从573 K继续升高到873 K时，表面形态明显变化，高温度退火导致材料中各类原子迁移、扩散，甚至Ga与Pd形成合金、氧化反应等效应更加剧烈，伴随着新生成的氧化钯和氧化镓的出现，原子台阶消失，显示出颗粒状特征" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "30", "type": "bibr", "rid": "R30", "data": [ { "name": "text", "data": "30" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "。有报道指出，载流子在非连续结构中传输受到间断和界面的影响，导电特性严重恶化" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "34", "type": "bibr", "rid": "R34", "data": [ { "name": "text", "data": "34" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，这是在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "和O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "混合条件下退火的典型形态" }, { "name": "sup", "data": [ { "name": "text", "data": "[" }, { "name": "xref", "data": { "text": "35", "type": "bibr", "rid": "R35", "data": [ { "name": "text", "data": "35" } ] } }, { "name": "text", "data": "]" } ] }, { "name": "text", "data": "，也再次验证了上述推论。" } ] }, { "name": "fig", "data": { "id": "F6", "caption": [ { "lang": "zh", "label": [ { "name": "text", "data": "图6" } ], "title": [ { "name": "text", "data": "4 nm Pd/p-GaN的AFM测试形貌。(a)未退火形貌;(b)N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛573 K退火形貌;(c)N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛873 K退火形貌;(d)超高真空873 K退火形貌。" } ] }, { "lang": "en", "label": [ { "name": "text", "data": "Fig.6" } ], "title": [ { "name": "text", "data": "AFM surface morphology of 4 nm Pd/p-GaN. (a)As-deposited morphology. (b)Annealed at 573 K in N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1 atmosphere. (c)Annealed at N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1 atmosphere in 873 K. (d)Annealed at 873 K under UHV.　" } ] } ], "subcaption": [], "note": [], "graphics": [ { "print": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352615&type=", "small": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352619&type=", "big": "http://html.publish.founderss.cn/rc-pub/api/common/picture?pictureId=21352618&type=" } ] } } ] }, { "name": "sec", "data": [ { "name": "sectitle", "data": { "title": [ { "name": "text", "data": "4　结论" } ], "level": "1", "id": "s4" } }, { "name": "p", "data": [ { "name": "text", "data": "结合XPS和AFM实验结果分析，研究了在退火过程中，退火温度、退火气氛对Pd/p-GaN的接触电阻率的影响。在室温下，当金属Pd溅射在洁净的p-GaN表面时，无论是来自溅射高能量粒子轰击带来的转移还是高温条件下的退火均有助于Ga-Pd合金相形成，并且随着厚度增加以及温度升高，Ga-Pd合金量增加。但是，在N" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "∶O" }, { "name": "sub", "data": [ { "name": "text", "data": "2" } ] }, { "name": "text", "data": "=4∶1气氛下，金属Pd、GaN与气氛中提供的氧发生反应生成氧化钯和氧化镓等氧化物，氧化物的产生掩盖了合金、互扩散效应成为主导因素，使得薄膜及接触等电性能迅速退化。因此，在器件制备工艺过程中，需要尽量避免GaN样品表面氧气残留，以避免后期高温处理过程中GaN界面处氧气参与。促使接触界面形成Ga-Pd等合金相，改善欧姆接触特性，防止界面氧化成为保证器件可靠且稳定重要的一个环节。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "感谢中国科学院苏州纳米技术与纳米仿生研究所Nano-X的技术支持。" } ] }, { "name": "p", "data": [ { "name": "text", "data": "本文专家审稿意见及作者回复内容的下载地址:http://cjl.lightpublishing.cn/thesisDetails#10.37188/CJL.20210092." } ] } ] } ], "footnote": [], "reflist": { "title": [ { "name": "text", "data": "参考文献:" } ], "data": [ { "id": "R1", "label": "[1]", "citation": [ { "lang": "en", "text": [ { "name": "text", "data": "WU Y" }, { "name": "text", "data": ", " }, { "name": "text", "data": "CHEN C Y" }, { "name": "text", "data": ", " }, { "name": "text", "data": "DEL ALAMO J A" }, { "name": "text", "data": ". 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