The authors thank Mr. Neil Green for assistance with sample preparation. This work was supported by the Office of Naval Research under funding from Dr. P. Maki. MTH was supported by a National Research Council Postdoctoral Fellowship.

1.积液细胞斜坡和流量校准<ol><li>确认液态氮的流向低温板和生长室已达到基本压力。 </li><li>斜坡上升的喷射室到其光束通量测量（BFM）温度以1℃/秒的升温速率为Ga和在细胞中，并为铝10℃/分钟。等待细胞1小时，热稳定。 </li><li>打开每个单元的快门为30-60秒，然后关闭快门1-2分钟。重复三次每个小区。丢弃第一束流离子规测量和平均后两种。调整电池温度根据先前通量/温度校准以获得所需的磁通。 </li></ol> 2.基板制备和加载<ol><li> 易地基板清洗 <ol><li>负载开盒即用的N-极性GaN衬底直接，没有任何易地清洗。如果晶片被暴露在空气中更超过几个小时，冲洗下丙酮（30秒），异丙醇（30秒）和去离子（DI）水（60秒）。漂洗优选浸没在可能的，因为它往往留在晶片表面上更小的颗粒。 注:有关嘎极性GaN衬底建议更严格的表面的清洁23 </li></ol></li><li> 装载晶圆 <ol><li>关闭负载锁隔离闸阀，并用N 2通气。 </li><li>装载在支架晶片和盒返回到负载锁定。打开负载锁定低真空泵，打开低真空泵阀和岐管阀。 </li><li>当歧管压力已降至低于0.1乇，关闭歧管和低真空泵阀。关掉低真空泵和打开装载锁定涡轮泵隔离阀。 </li><li>允许负载锁定抽空30-60分钟。理想情况下，使用10 -6 -10 -7托的负载锁定压力转移到准备室前。 </li><li>打开负载锁定到制备腔室，并且使用摆动棒晶片传送到手推车。然后用台车到晶片在制备腔室传送到除气站。手动移动台车沿着上使用该准备容室的旋转穿通线的轨道。 </li></ol></li><li> 脱气晶圆 <ol><li>斜坡除气站加热器温度到700℃历时10分钟。 </li><li> 30分钟后，递减的温度回落到100℃。当温度≤250℃，使用该摆动棒在除气站传送晶片返回到手推车。 </li></ol></li><li> 负载晶片到生长室 <ol><li>降低基板操纵到装载位置，打开准备/生长室闸阀和晶片保持器传送到操纵器。 </li><li>抬起手来生长部位，基底加热器附近。 </li><li>取出小车和ClOSE闸阀。 </li><li>打开N 2瓶头阀，调节阀和隔离针形阀。设置质量流量控制器（MFC）以1.5标准立方厘米（或根据需要以得到3-4×10 -5乇的室压力）。对于等离子点火的最佳压力是强烈依赖于系统。注意，N 2必须是超高纯度（大于6N优选更好）和一个附加滤波在线路用于进一步降低杂质。 </li><li>与N *和主百叶窗关闭时，打开等离子体RF电源和自动匹配网络控制器。加大射频功率，直到血浆点燃。 </li><li>设置RF功率和N 2流量为所需的工艺条件，在这种情况下，350瓦和2.0标准立方厘米。从给定的等离子体条件所产生的N *通量系统相关，但在这里，这些条件屈服的5.0纳米/分钟的GaN生长速度，或1.8纳米-2秒的N *通量-1。监控与连接到一台光谱仪的血浆稳定性等离子体室的后窗。 </li></ol></li><li> 原位表面处理:嘎沉积和解吸 <ol><li>衬底加热器斜坡上升至10℃，高于所需的GaN生长温度与≤1℃/秒的升温速率。在这种情况下使用的730℃的估计晶片温度。 </li><li>打开RHEED系统上观看的晶片表面的劣化和监测镓覆盖。手动打开基板转动。设置了触发RHEED采集软件每衬底旋转一次收集的RHEED图案同时衬底生长过程中旋转，以提供一个静态图像。 </li><li>打开衬底快门和Ga快门1分钟。确保RHEED强度减小那么作为嘎积累达到平稳。 Ga束流的应类似于用于GaN生长。在此，Ga束流为大约3.7纳米-2秒-1。 </li><li>关闭快门2分钟，并确保RHEED强度增加并达到2分钟结束前一个平台，表明嘎解吸。 </li><li>重复步骤2.5.2-2.5.4三次，24然后斜衬底的GaN生长的温度。 </li></ol></li></ol> 3. HEMT增长<ol><li> 缓冲区增长 <ol><li>通过打开N *快门对于1分钟氮化开始生长。 </li><li>通过打开铝快门长出薄薄的1-3纳米丰富的N- AlN成核层。此AlN层可以帮助防止穿透位错的产生，25然而，在AlN层复杂的X射线衍射（XRD）测量，不推荐基于XRD-校准样品。使用相同的Al磁通作为InAlN层，或约0.36纳米-2秒-1，给予大约为1纳米/分钟的生长速率。 </li><li>关闭Al和N *快门和立即打开嘎快门10秒，让嘎饱和从表面上看，RHEED强度应减少RApidly。打开N *快门（以尕快门仍然打开），并增加5分钟的GaN。使用成为或C掺杂，特别是对独立GaN衬底，防止在缓冲漏电电流。 </li><li>关闭Ga和N *百叶窗1分钟生长中断。监测RHEED强度。如果RHEED强度立即增大，则Ga束流不够高。如果RHEED强度&gt; 30秒之后增加或没有达到1分钟内的高原则Ga束流的过高。参见图3。 </li><li>增加几度基板温度（或减少镓喷射室温度），以补偿在3.1.4看到高镓通量。如果Ga的流量为过低，降低基板温度（或者增加Ga的喷射室温度）进行补偿。 <ol><li>重复步骤3.1.3-3.1.5，直到有一个15-30秒的延迟RHEED强度增加并且RHEED强度达到前1分钟的高原之前。 </li></ol></LI&gt; <li>继续重复步骤3.1.4-3.1.5直到达到所需的GaN的厚度。由校准增长率乘以总的生长时间确定的厚度。对于富Ga生长，确定由N *通量，其可以反过来采用XRD测量为一个单独生长校准样品以已知的生长时间的厚度来计算的增长率。 </li></ol></li><li> InAlN屏障增长 <ol><li>再等待1分钟，最后GaN生长步骤后，以确保所有嘎蒸发。 </li><li>急剧下降到InAlN生长温度约为630℃。允许将基板温度稳定约2分钟。 </li><li>打开In，Al和N *百叶窗。该RHEED强度应该减少与前3分钟内到达平台期。 RHEED强度的持续下降可以指示在积累，这是不利的InAlN增长。 RHEED图应保持条纹，表明表面光滑。我的n和铝通量约为0.31和0.36纳米-2秒-1，给予的1.25纳米/分钟III族有限的增长速度。 </li><li>关闭在，Al和N *所需的阻挡层厚度后百叶窗已经达到。对于富的N-增长，确定由总III族流量的增长速度。测量使用一个单独生长InAlN校准样品的XRD的增长速度。对于使用这里给出的条件15nm的InAlN屏障，打开百叶窗12分30秒。 </li></ol></li><li> 夹层和渠道增长 <ol><li>首先打开嘎快门5秒，然后打开N *快门和生长的GaN中间层。基板温度应该仍然在InAlN生长温度。 </li><li>打开铝快门，无需关闭或Ga N *百叶窗成长的AlN的中间层。用于中间层的的Al通量应大于N *磁通相同或稍高，最好使用不同的Al渗出细胞然后与用于InAlN阻挡层，叔o避免不必更改电池温度。请参阅步骤3.2.4。 </li><li>关闭N *和Al百叶窗，但离开嘎快门打开。坡道衬底温度达到GaN沟道温度。 </li><li> 30秒后关闭嘎快门。等待30秒（或者只要RHEED强度开始增加），并重新打开嘎快门。继续循环镓快门直到基板已达到GaN沟道生长温度。这将同时防止过度积累嘎保护表面。 </li><li>打开嘎快门5秒，然后打开N *快门和成长GaN沟道。 </li><li>关闭嘎，N *及主要百叶窗。坡道使基板温度下降到200℃，关掉N *等离子体和关闭的 N 2气流。 </li><li>斜坡细胞下降到待机温度，如果完成的一天。 </li><li>等待将衬底温度降低低于250℃，腔室压力下降到低于8×10 -7乇，然后打开生长室闸阀和晶片支架传送回手推车。 </li><li>按照步骤2.2到晶片传送回负载锁定的反向，泄用N 2和取出晶片。确保生长室闸阀被打开负载锁定之前闭合，并且该负载锁定涡轮泵闸阀放空之前关闭。 </li><li>按照步骤2.2.3-2.2.5到磁带盒和负载锁定回到高真空。 </li></ol></li></ol> 4.表征<ol><li>利用光学显微镜来检查可能的渠道增长过程中形成的凹坑，裂纹或Ga液滴，XRD检查界面和结构质量，原子力显微镜来检查表面形貌表征材料的品质。20,21 </li><li>如果Ga的液滴存在，沉浸在浓HF酸晶片5-10分钟以除去液滴而不损坏化学敏感N极性面。 </li><li>测量表水库istance使用Lehighton的接触电阻的测量。 </li><li>处理样品，让电器特性，包括大厅和CTLM测量，直流和射频晶体管特性。9,26 </li></ol>

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C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Oxygen+incorporation+in+homoepitaxial+N-polar+GaN+grown+by+radio+frequency-plasma+assisted+molecular+beam+epitaxy:+Mitigation+and+modeling.">Oxygen incorporation in homoepitaxial N-polar GaN grown by radio frequency-plasma assisted molecular beam epitaxy: Mitigation and modeling.</a> J. Appl. Phys. 112 (1), 013507 (2012).</li><li>Storm, D. F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effect+of+interfacial+oxygen+on+the+microstructure+of+MBE-grown+homoepitaxial+N-polar.">Effect of interfacial oxygen on the microstructure of MBE-grown homoepitaxial N-polar.</a> J. Cryst. Growth. 409, 14 (2014).</li><li>Meyer, D. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+Electron+Velocity+Submicrometer+AlN/GaN+MOS-HEMTs+on+Freestanding+GaN+Substrates.">High Electron Velocity Submicrometer AlN/GaN MOS-HEMTs on Freestanding GaN Substrates.</a> IEEE Electron Device Lett. 34, 199 (2013).</li><li>Moseley, M., Billingsley, D., Henderson, W., Trybus, E., Doolittle, W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transient+atomic+behavior+and+surface+kinetics+of+GaN.">Transient atomic behavior and surface kinetics of GaN.</a> J. Appl. Phys. 106 (1), 014905 (2009).</li><li>Koblm&#252;ller, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ga+Adlayer+Governed+Surface+Defect+Evolution+of+(0001)GaN+Films+Grown+by+Plasma-Assisted+Molecular+Beam+Epitaxy.">Ga Adlayer Governed Surface Defect Evolution of (0001)GaN Films Grown by Plasma-Assisted Molecular Beam Epitaxy.</a> Jpn. J. Appl. Phys. 44 (28), L906-L908 (2005).</li><li>Poblenz, C., Waltereit, P., Speck, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Uniformity+and+control+of+surface+morphology+during+growth+of+GaN+by+molecular+beam+epitaxy.">Uniformity and control of surface morphology during growth of GaN by molecular beam epitaxy.</a> J. Vac. Sci. Technol., B. 23 (4), 1379-1385 (2005).</li></ol>

The authors have nothing to disclose.

高品质的GaN缓冲层的生长是在任何III族氮化物HEMT实现高电子迁移率的关键。在N极性InAlN HEMT的情况下，缓冲层生长是由所有镓从InAlN生长之前的表面去除的要求变得复杂。有各种技术，除了程序来完成此这里描述的，例如金属调制外延，27使用的生长条件在中间镓覆盖率和Ga液滴积累制度，28的边缘或允许连续N * -磁通掺入过量嘎当嘎快门被周期性关闭。24 一个成长型中断（允许嘎蒸发）在这种情况下，因为它减少了磨损金属调制外延隐百叶窗时，是宽容的晶圆温度不均匀，29，避免在实际生长时间模糊（和层厚度）作为WELl由于防止潜在杂质掺入作为使用N- *磁通以合并Ga的浸润层的结果。在条纹状的RHEED和光滑的表面/界面24这一技术的结果与均方根粗糙度&lt;1纳米，如果正确Ga的磁通和生长/中断次使用。除了在图3中描述的RHEED瞬变，Ga的磁通不足可以通过参差不齐RHEED图案和粗糙表面（富N-二条件）或条纹状的RHEED与高原/沟槽粗糙的表面形态（为富镓中间体来指示条件）。28 中断之间的最大生长时间有点柔性的，但由宏观Ga的液滴形成的限制。一旦液滴形式和聚结，它们很难充分蒸发，仍然可以发生在镓的液滴的存在RHEED增亮，错误地提示有Ga的自由表面。的中断之间达20分钟的GaN生长时间已被用于与r得出快门磨损。29生长后在晶片表面上发现可以从在缓冲层生长过程中形成的液滴起源（尽管他们可在不显著负面后果GaN沟道生长期间也形成）Ga的液滴。该缓冲期间形成宏观Ga的液滴可导致在镓掺入和/或位移的InAlN阻挡层中，从而降低载流子浓度和/或由于应变的阻挡层，这是在较低的温度区域更严重的开裂的晶片。 在增长或接近通道的中断可能会导致严重的器件退化的HEMT器件。然而，如果Ga的磁通周期性地供给，并允许在中断期间解吸，在流动性的劣化能够避免，中断可用于衬底加速到更高的生长温度为GaN生长15使用这种技术更有利的，迁移率已经增加了大约150厘米<s&gt; 2 / V∙秒相对于样品在InAlN生长温度生长GaN沟道起来。的GaN和/或氮化铝夹层之前，必须增加生长温度，以免损坏表面InAlN增长。 我们已经证明生长高质量N极性InAlN阻HEMT器件的方法。 原位镓沉积和解吸被利用来为外延生长准备清洁的表面。的HEMT的外延层结构结合有均匀的组合物，的AlN和GaN中间层来控制沟道电荷密度和流动性，并与一个温度斜坡可进一步优化迁移率的GaN沟道生长过程的InAlN阻挡层。 PAMBE和此处描述的方法广泛适用于III族氮化物外延，包括RF和高功率电子和可见 - 通过紫外线光电子。

分子束外延（MBE）是一种多功能的外延薄膜生长技术，其用碱的压力低至10 -11乇采用的超高真空环境，以确保在生长膜低杂质掺入。外延生长层的组成和生长速率是通过控制每一个喷射室的温度，并且因此各种源物质的蒸发通量测定。在III族氮化物外延，Ⅲ族元素（在，铝，镓），而活性氮（N *）磁通由任一的N 2等离子体1,2-（RF等离子体提供通常由喷射室中提供的基的情况下-assisted MBE:PAMBE或RFMBE）或氨（NH 3 -MBE）3,4- MBE生长的5特征在于较低的生长温度和更清晰的界面陡峭比其他的外延生长技术，如金属有机化学气相沉积的示意图被示出。在图1中。 <p类="jove_content"&gt; <img alt="图1" src="/files/ftp_upload/54775/54775fig1.jpg" /> 图1:。MBE系统原理示意图，显示加载锁定，传送系统，除气站和生长室<a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54775/54775fig1large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> III族氮化物可以在具有各种晶体取向衬底上生长。最常用的取向是镓极性的c面，它允许的二维电子气的形成而不掺杂通过利用阻挡层，通常AlGaN和GaN沟道之间偏振差。氮化镓的各种非极性和半极性方向已收到光电子显著注意由于在量子阱，这也使得这些取向不太希望为HEMT应用A 6,7-减小极化效应纳秒。 N极性导向设备是用于下一代高频HEMT操作有吸引力，由于比常规镓极性设备几个固有的优点。8在N极性装置的阻挡层生长在GaN沟道下方， 如图2，所得在自然回屏障有助于该信道的静电控制和减少短沟道效应，同时允许容易当前接入到GaN沟道和减少接触电阻。阻挡也可以从通道分别控制，这样，当信道厚度按比例缩小的用于高频器件的屏障设计可以被修改，以补偿失去的费米能级钉扎效应信道的费用。 <img alt="图2" src="/files/ftp_upload/54775/54775fig2.jpg" /> 图2:（a）一种N极性HEMT和（b）一种镓极性HEMT为COMPAR的外延层概略层结构ISON。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54775/54775fig2large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> 在高速使用HEMT器件，高功率放大器通常生长在SiC衬底采取SiC的高热导率的优点。低的穿透位错密度的独立式GaN衬底可以被用来提高电子迁移率，9从而改善高频性能。以下的AlN成核层的生长，一个厚的GaN缓冲生长到空间中的杂质在离HEMT信道的再生长界面分离并改善电隔离。不像其他的III-V材料，氮化镓由PAMBE生长通常需要的生长条件与一组-III / V比大于1， 即 ，富金属的条件下，10,11，以达到平滑的表面形态更大。 x中铝1×N的是一个ALTER天然阻挡材料为III族氮化物HEMT器件，并已收到显著关注最近，因为它可以生长晶格匹配的GaN对于x≈0.18，并可以在相对的AlGaN障碍两次沟道电荷由于其高自发极化产生12-15不同于的AlGaN障碍，镓将优先结合到在InAlN层，16因而必须小心，以确保富Ga GaN缓冲层的生长和InAlN生长之前后的表面是自由过量的Ga。 镓的表面上控制可以通过suppling Ga的磁通比Ga的液滴形成所需的磁通稍小来完成。然而，这种增长窗口小，并且不足镓表面覆盖将导致表面形态降解成高原/沟槽的形态，而过量的Ga束流会导致镓积累和宏观液滴形成。17反射高能电子衍射（RHEED）INTENS<html>性可用于监测镓积累和解吸。ガ表面覆盖率是通过RHEED强度降低，和关闭ガ之间任何滞后指示（和N *）百叶窗和在RHEED强度的初始增加表明镓累积， 如图3。 <img alt="图3" src="/files/ftp_upload/54775/54775fig3.jpg" /> 图3:监控嘎覆盖，使用触发采集下旋转收购RHEED模式计量的RHEED强度 RHEED强度信号。 （未示出）不足Ga束流通过关闭快门之后立即增加强度指示。饱和/理想嘎覆盖率由快门关闭和突然的RHEED增白和多余嘎覆盖率视为初始RHEED增亮两个延迟以及导致全强度恢复较为缓慢强度增加的时间超过60秒之间的延迟表示。COM /文件/ ftp_upload / 54775 / 54775fig3large.jpg"目标="_空白"&gt;点击此处查看该图的放大版本。 实现高品质通过PAMBE InAlN由横向成分波动的存在复杂的，导致由以富以界包围富铝域的"蜂窝"的微观结构。此微结构18消除是通过使用基板温度约50取得℃下在解吸，15,19,20或约630℃，N极性InAlN发作以上。在这种高温下生长机制，则在具有In x Al 1-×N个组合物是衬底温度的强函数，以导致较低的掺入更高的温度。该通量可以增加以补偿蒸发掉，但实际上最大的在流量由掺入效率的降低与增加流量限制21除了降低衬底温度或增加在通量，增加生长速度也可以增加在组合物由于"以掩埋效应"，其中，进入的铝原子陷阱以及防止其蒸发。21,22高等生长速率可以通过按比例增加的In和Al通量来实现。为了保持生长条件Ñ富中，N *将需要以及增加，这可以通过增加RF等离子体功率来实现，增加的 N 2流量，改善了等离子体室设计，或者增加光圈板孔密度。 在基于InAlN类HEMT额外外延层包括GaN和AlN中间层（离子液体）和GaN沟道。 AlN的IL插入的屏障和渠道之间能增加流动性μ以及沟道薄层电荷密度N s 个 。在移动性的增加归因于减少与InAlN B电子波函数重叠arrier和随后的合金散射。9为确保在AlN的IL高质量的增长，过量的Ga束流的生长过程中供给到充当表面活性剂。的GaN的IL可以在AlN IL和屏障之间使用，以进一步改善流动性，同时减少信道的费用。 GaN沟道可以在相同的温度下InAlN屏障来生长，允许从阻挡尽管离子液体和信道持续增长。改进的流动性已经被中断的AlN IL后生长和生长所述GaN沟道之前增加的生长温度下得到。在这种情况下的保护镓表面覆盖有中断，以防止流动性降解过程中被保持。 下面的协议特别适用于生长在N极性GaN衬底InAlN屏障HEMT器件。它可以通过包括一个50纳米厚的n富AlN层可以直接延伸到第C-极性4H-或6H-SiC衬底的生长。

<table border="0" cellpadding="0" cellspacing="0" width="749">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">Freestanding N-polar GaN wafer</td>
			<td style="width:145px;">Kyma</td>
			<td style="width:128px;"></td>
			<td style="width:167px;">10 mm x 10 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">C-polar SiC wafer</td>
			<td style="width:145px;">Cree</td>
			<td style="width:128px;">W4TRE0R-L600</td>
			<td>3 inch diameter</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">Microelectronics grade acetone</td>
			<td style="width:145px;">Fischer Scientific</td>
			<td style="width:128px;">A18-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">Microelectronics grade isoproponal</td>
			<td style="width:145px;">J.T. Baker</td>
			<td style="width:128px;">9079-05/JT9079-5</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">Al source material (6N5 pure)</td>
			<td style="width:145px;">UMC</td>
			<td>ALR62060I</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">Ga source material (7N pure)</td>
			<td style="width:145px;">UMC</td>
			<td>GA701</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">In source material (7N pure)</td>
			<td style="width:145px;">UMC</td>
			<td>IN750</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">ULSI N2 source gas (6N pure)</td>
			<td style="width:145px;">Matheson Tri-gas</td>
			<td>G2659906D</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:309px;">PRO-75 MBE system</td>
			<td style="width:145px;">OmicronScientia</td>
			<td style="width:128px;"></td>
			<td></td>
		</tr>
	</tbody>
</table>

plasma-assisted molecular beam epitaxy of n-polar inaln-barrier high-electron-mobility transistors

等离子体辅助分子束外延非常适合于III族氮化物薄膜和异质的具有高品质的高电子迁移率晶体管（HEMT器件）需要平滑，突变接口外延生长。的过程提出了N极性InAlN HEMT器件的生长，包括晶圆制备和缓冲层，所述InAlN阻挡层的AlN和GaN中间层和GaN沟道的生长。在该过程的每个步骤中的关键问题被识别，如避免在GaN缓冲嘎积累，温度对InAlN组成均一性的作用，以及在AlN层间期间使用Ga束流的和中断的GaN之前信道的增长。组成均匀N极性InAlN薄膜，证明用低至0.19纳米和表面根均方粗糙度InAlN基于被报告的HEMT结构具有带片电荷密度迁移率高达1750厘米2 / V∙秒为设备为1.7×1013厘米-2。

X射线衍射（XRD）上生长图4中N极性GaN衬底所示InAlN薄膜的扫描（a）的单峰值都为50和200纳米厚的薄膜。 50纳米厚的薄膜InAlN的XRD扫描表现Pendellösung条纹高达15 阶 ，显示非常高的界面质量。 图4中的非对称倒易空间映射（b）示出了200nm厚InAlN层具有相同q‖，因此在同一平面内晶格常数为GaN衬底，指示用于一个合理的厚InAlN层完全一致的增长。半最大值（FWHM）在第q‖方向的全宽度是非常接近相同的InAlN层和GaN衬底，这表明没有额外的位错或其它结构缺陷已在InAlN层被引入。在Q⊥的InAlN层的扩大是有限的连贯性造成的lenGTH在较薄InAlN层扩大。 在图5所示的AFM图像比较两个在0.18的Al 0.82 N个层具有类似组合物在500℃和630℃下生长。达到相同的组合物中，以/ III族磁通比从0.18在500℃在630℃升高到0.47。在较低的生长温度，其表面表示准三维生长模式中，当步骤被认为在630℃样品，表明2D步骤-流动生长。透射电子显微照片示出了蜂窝形态的消除在高温下生长在0.18的Al 0.82 N个采样。19,20 图6中所示生长在N极性GaN衬底充满N极性InAlN阻HEMT结构的X射线衍射测量（a）用X射线衍射模拟吻合。该模拟是对所有的敏感各层，及该协议表示两个界面的良好的品质和在各个层厚度较高程度的控制。在AlN和GaN IL厚度分别为1.4和1.5海里，分别。霍尔效应测量导致测量μ=1400厘米2 / V∙秒中，n S = 2.2×10 13 cm 2以下，而R 5 = 200Ω/□。 N极对生长在C-极性SiC和N极性的GaN衬底的外延层通过比较测试结构和充分的HEMT结构的薄层电阻证实。仅具有生长于GaN或氮化镓/ AlN缓冲层的InAlN层样品高电阻，表明不存在二维电子气。与上InAlN层的顶部上的GaN沟道样品显示出低薄层电阻从霍尔测量的二维电子气的170-300Ω/□和证据，证实N极性奥里ntation。 基于初始材料特性，样品可以被加工成HEMT器件。处理的第一阶段涉及在沉积钛/铝/镍/金（20/100/10/50纳米）下的 N 2环境欧姆接触通过电子束蒸发和退火在750℃下30秒，随后通过器件隔离使用C18 2 / BCL 3 /氩感应耦合等离子蚀刻。对于这里所讨论的设备的源 - 漏间隔为5μm。在这一点上几个过程监控结构可以电测试，包括直线，圆弧传输长度测量模式板材和接触电阻和霍尔效应图案通道电荷密度和流动性。所选样本再全HEMT结构由沉积1微米长，150微米宽的Pt /金门处理。与上述的外延结构的HEMT中生长的N极性GaN衬底上并有Pt / Au的制造<html>肖特基栅极显示出优异的直流特性，以1.5的A /毫米的最大电流（为一个5微米的源-漏间隔和未优化触点）和-1.6伏的阈值电压， 如图6。 <img alt="图4" src="/files/ftp_upload/54775/54775fig4.jpg" /> 图4:InAlN薄膜的X射线衍射 （ 一 ）2θ/ω生长在独立的N-极性衬底和（b）的XRD倒易空间映射有关的反射，呈现为50nm和200nm厚的InAlN薄膜的XRD衍射扫描200纳米厚的一层InAlN具有相同q‖协调，因此一致的GaN衬底。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54775/54775fig4large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> ftp_upload / 54775 / 54775fig5.jpg"/&gt; 图5:在（ 一 ）500℃下的0.18的In / III族比和（b）630℃，用在/ III族生长在0.18的Al 0.82 N个样本的InAlN薄膜的原子力显微镜 AFM显微照片0.47的比例。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54775/54775fig5large.jpg" target="_blank">请点击此处查看该图的放大版本。</a> <img alt="图6" src="/files/ftp_upload/54775/54775fig6.jpg" /> 数字。 6:一个InAlN HEMT的XRD和设备的结果 （ 一 ）的XRDω/2θ扫描大约生长与用于生成X射线衍射模拟插图层厚度的N极性GaN衬底上的全N极性InAlN HEMT结构的0002反射。 。 （ 二 ）HEMT转移曲线和（c）为（a）中PROCES同一装置IV曲线SED与PT /金肖特基门。 <a href="https://ecsource-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/54775/54775fig6large.jpg" target="_blank">请点击此处查看该图的放大版本。</a>

Watch this Scientific Journal Video about Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors at JoVE.com

Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

分子束外延用来生长N极性InAlN阻高电子迁移率晶体管（HEMT器件）。在光滑，组成均匀InAlN层和HEMT的晶圆准备控制层生长条件和外延结构的结果与流动性高达1750厘米2 / V∙秒。

N极性InAlN阻高电子迁移率晶体管的等离子体辅助分子束外延

Plasma-assisted molecular beam epitaxy is well suited for the epitaxial growth of III-nitride thin films and heterostructures with smooth, abrupt ...

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Nanyang Technological University

Research

JoVE Journal

Engineering

8.5K 次观看.  Naval Research Laboratory. 分子束外延用来生长N极性InAlN阻高电子迁移率晶体管（HEMT器件）。在光滑，组成均匀InAlN层和HEMT的晶圆准备控制层生长条件和外延结构的结果与流动性高达1750厘米2 / V∙秒。 

视频: Plasma-assisted Molecular Beam Epitaxy of N-polar InAlN-barrier High-electron-mobility Transistors

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet (VUV) Synchrotron Radiation

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy and dynamics1-4. Fundamental studies of photoionization processes of biomolecules provide information about the electronic structure of these systems. Furthermore determinations of ionization energies and other properties of biomolecules in the gas phase are not trivial, and these experiments provide a platform to generate these data. We have developed a thermal vaporization technique coupled with supersonic molecular beams that provides a gentle way to transport these species into the gas phase. Judicious combination of source gas and temperature allows for formation of dimers and higher clusters of the DNA bases. The focus of this particular work is on the effects of non-covalent interactions, i.e., hydrogen bonding, stacking, and electrostatic interactions, on the ionization energies and proton transfer of individual biomolecules, their complexes and upon micro-hydration by water1, 5-9.
We have performed experimental and theoretical characterization of the photoionization dynamics of gas-phase uracil and 1,3-dimethyluracil dimers using molecular beams coupled with synchrotron radiation at the Chemical Dynamics Beamline10 located at the Advanced Light Source and the experimental details are visualized here. This allowed us to observe the proton transfer in 1,3-dimethyluracil dimers, a system with pi stacking geometry and with no hydrogen bonds1. Molecular beams provide a very convenient and efficient way to isolate the sample of interest from environmental perturbations which in return allows accurate comparison with electronic structure calculations11, 12. By tuning the photon energy from the synchrotron, a photoionization efficiency (PIE) curve can be plotted which informs us about the cationic electronic states. These values can then be compared to theoretical models and calculations and in turn, explain in detail the electronic structure and dynamics of the investigated species 1, 3.

Molecular Beam Mass Spectrometry With Tunable Vacuum Ultraviolet VUV Synchrotron Radiation

A molecular beam coupled to tunable vacuum ultraviolet photoionization mass spectrometer at a synchrotron provides a convenient tool to explore the electronic structure of isolated gas phase molecules and clusters. Proton transfer mechanisms in DNA base dimers were elucidated with this technique.

可调式真空紫外（VUV）同步辐射分子束质谱分析

Tunable soft ionization coupled to mass spectroscopy is a powerful method to investigate isolated molecules, complexes and clusters and their spectroscopy ...

科研

工程学

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

分子构象器和星团的空间分离

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Measurement of X-ray Beam Coherence along Multiple Directions Using 2-D Checkerboard Phase Grating

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is reported. The measurements were demonstrated at the 1-BM bending magnet beamline of the Advanced Photon Source (APS) at Argonne National Laboratory (ANL). By using a 2-D checkerboard &#960;/2 phase-shift grating, transverse coherence lengths were obtained along the vertical and horizontal directions as well as along the 45&#176; and 135&#176; directions to the horizontal direction. Following the technical details specified in this paper, interferograms were measured at different positions downstream of the phase grating along the beam propagation direction. Visibility values of each interferogram were extracted from analyzing harmonic peaks in its Fourier Transformed image. Consequently, the coherence length along each direction can be extracted from the evolution of visibility as a function of the grating-to-detector distance. The simultaneous measurement of coherence lengths in four directions helped identify the elliptical shape of the coherence area of the Gaussian-shaped X-ray source. The reported technique for multiple-direction coherence characterization is important for selecting the appropriate sample size and orientation as well as for correcting the partial coherence effects in coherence scattering experiments. This technique can also be applied for assessing coherence preserving capabilities of X-ray optics.

The measurement protocol and data analysis procedure are given for obtaining transverse coherence of a synchrotron radiation X-ray source along four directions simultaneously using a single 2-D checkerboard phase grating. This simple technique can be applied for complete transverse coherence characterization of X-ray sources and X-ray optics.

使用2-D棋盘相位光栅X射线束相干测量沿多个方向

A procedure for a technique to measure the transverse coherence of synchrotron radiation X-ray sources using a single phase grating interferometer is ...

Speciation and Bioavailability Measurements of Environmental Plutonium Using Diffusion in Thin Films

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can potentially contribute to the exposure of biota and humans. The diffusive gradients in thin films technique is introduced here for in-situ measurements of Pu bioavailability and speciation. A diffusion cell constructed for laboratory experiments with Pu and the newly developed protocol make it possible to simulate the environmental behavior of Pu in model solutions of various chemical compositions. Adjustment of the oxidation states to Pu(IV) and Pu(V) described in this protocol is essential in order to investigate the complex redox chemistry of plutonium in the environment. The calibration of this technique and the results obtained in the laboratory experiments enable to develop a specific DGT device for in-situ Pu measurements in freshwaters. Accelerator-based mass-spectrometry measurements of Pu accumulated by DGTs in a karst spring allowed determining the bioavailability of Pu in a mineral freshwater environment. Application of this protocol for Pu measurements using DGT devices has a large potential to improve our understanding of the speciation and the biological transfer of Pu in aquatic ecosystems.

The technique of diffusive gradients in thin films (DGT) is proposed for speciation studies of plutonium. This protocol describes diffusion experiments probing the behavior of Pu(IV) and Pu(V) in presence of organic matter. DGTs deployed in a karstic spring allow assessment of the bioavailability of Pu.

环境钚的薄膜弥散形态和生物利用度测量

The biological uptake of plutonium (Pu) in aquatic ecosystems is of particular concern since it is an alpha-particle emitter with long half-life which can ...

Effect of Bending on the Electrical Characteristics of Flexible Organic Single Crystal-based Field-effect Transistors

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling immensely. However, in soft electronics, in which organic semiconductors play a critical role, the devices will be bent or folded repeatedly. The effect of bending on the crystal packing and thus the charge transport is crucial to the performance of the device. In this manuscript, we describe the protocol to bend a single crystal of 5,7,12,16-tetrachloro-6,13-diazapentacene (TCDAP) in the field-effect transistor configuration and to obtain reproducible I-V characteristics upon bending the crystal. The results show that bending a field-effect transistor prepared on a flexible substrate results in nearly reversible yet opposite trends in charge mobility, depending on the bending direction. The mobility increases when the device is bent toward the top gate/dielectric layer (upward, compressive state) and decreases when bent toward the crystal/substrate side (downward, tensile state). The effect of bending curvature was also observed, with greater mobility change resulting from higher bending curvature. It is suggested that the intermolecular &#960;-&#960; distance changes upon bending, thereby influencing the electronic coupling and the subsequent carrier transport ability.

This manuscript describes the bending process of an organic single crystal-based field-effect transistor to maintain a functioning device for electronic property measurement. The results suggest that bending causes changes in the molecular spacing in the crystal and thus in the charge hopping rate, which is important in flexible electronics.

弯曲对基于晶体的柔性有机单场效应晶体管的电气特性的影响

The charge transport in an organic semiconductor depends highly on the molecular packing in the crystal, which influences the electronic coupling ...

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of lithium-ion (Li-ion) batteries. However, a number of setbacks prevent their integration into commercial devices. The main limiting factor is due to nanoscale phenomena occurring at the electrode/electrolyte interfaces, ultimately leading to degradation of battery operation. These key problems are highly challenging to observe and characterize as these batteries contain multiple buried interfaces. One approach for direct observation of interfacial phenomena in thin film batteries is through the fabrication of electrochemically active nanobatteries by a focused ion beam (FIB). As such, a reliable technique to fabricate nanobatteries was developed and demonstrated in recent work. Herein, a detailed protocol with a step-by-step process is presented to enable the reproduction of this nanobattery fabrication process. In particular, this technique was applied to a thin film battery consisting of LiCoO2/LiPON/a-Si, and has further been previously demonstrated by in situ cycling within a transmission electron microscope.

Focused Ion Beam Fabrication of LiPON-based Solid-state Lithium-ion Nanobatteries for In Situ Testing

A protocol for the fabrication of electrochemically active LiPON-based solid-state lithium-ion nanobatteries using a focused ion beam is presented.

基于 LiPON 的固态锂离子 Nanobatteries 的聚焦离子束制备方法在原位测试中的研究

Solid-state electrolytes are a promising replacement for current organic liquid electrolytes, enabling higher energy densities and improved safety of ...

Fabrication of Schottky Diodes on Zn-polar BeMgZnO/ZnO Heterostructure Grown by Plasma-assisted Molecular Beam Epitaxy

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device applications. Zinc oxide (ZnO), a semiconductor with a wide bandgap (3.4 eV) and high electron saturation velocity has gained a great deal of attention as an attractive material for high speed devices. Efficient gate modulation, however, requires high-quality Schottky contacts on the barrier layer. In this article, we present our Schottky diode fabrication procedure on Zn-polar BeMgZnO/ZnO heterostructure with high density 2DEG which is achieved through strain modulation and incorporation of a few percent Be into the MgZnO-based barrier during growth by molecular beam epitaxy (MBE). To achieve high crystalline quality, nearly lattice-matched high-resistivity GaN templates grown by metal-organic chemical vapor deposition (MOCVD) are used as the substrate for the subsequent MBE growth of the oxide layers. To obtain the requisite Zn-polarity, careful surface treatment of GaN templates and control over the VI/II ratio during the growth of low temperature ZnO nucleation layer are utilized. Ti/Au electrodes serve as Ohmic contacts, and Ag electrodes deposited on the O2 plasma pretreated BeMgZnO surface are used for Schottky contacts.

Attainment of high-quality Schottky contacts is imperative for achieving efficient gate modulation in heterostructure field effect transistors (HFETs). We present the fabrication methodology and characteristics of Schottky diodes on Zn-polar BeMgZnO/ZnO heterostructures with high-density two dimensional electron gas (2DEG), grown by plasma-assisted molecular beam epitaxy on GaN templates.

等离子体辅助分子束外延法制备的锌极性 BeMgZnO/氧化锌异质结构肖特基二极管的制备

Heterostructure field effect transistors (HFETs) utilizing a two dimensional electron gas (2DEG) channel have a great potential for high speed device ...

Single-Digit Nanometer Electron-Beam Lithography with an Aberration-Corrected Scanning Transmission Electron Microscope

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by employing an aberration-corrected scanning transmission electron microscope as the exposure tool. Here, we present results of single-digit nanometer patterning of two widely used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. The method achieves sub-5 nanometer features in poly (methyl methacrylate) and sub-10 nanometer resolution in hydrogen silsesquioxane. High-fidelity transfer of these patterns into target materials of choice can be performed using metal lift-off, plasma etch, and resist infiltration with organometallics.

We use an aberration-corrected scanning transmission electron microscope to define single-digit nanometer patterns in two widely-used electron-beam resists: poly (methyl methacrylate) and hydrogen silsesquioxane. Resist patterns can be replicated in target materials of choice with single-digit nanometer fidelity using liftoff, plasma etching, and resist infiltration by organometallics.

用畸变校正扫描透射电镜进行单数字纳米电子束光刻

We demonstrate extension of electron-beam lithography using conventional resists and pattern transfer processes to single-digit nanometer dimensions by ...

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh

A methodology is described to generate an isotopically pure 229Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the low-lying isomeric first excited state of 229Th at an excitation energy of about 7.8(5) eV and a radiative lifetime of up to 104 seconds. The presented method allowed for a first direct identification of the decay of the thorium isomer, laying the foundations to study its decay properties as prerequisite for an optical control of this nuclear transition. High energy 229Th ions are produced in the &#945;&#160;decay of a radioactive 233U source. The ions are thermalized in a buffer-gas stopping cell, extracted and subsequently an ion beam is formed. This ion beam is mass purified by a quadrupole-mass separator to generate a pure ion beam. In order to detect the isomeric decay, the ions are collected on the surface of a micro-channel plate detector, where electrons, as emitted in the internal conversion decay of the isomeric state, are observed.

Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh

We present a protocol for the generation of an isotopically purified low-energy 229Th ion beam from a 233U source. This ion beam is used for the direct detection of the 229mTh ground-state decay via the internal-conversion decay channel. We also measure the internal conversion lifetime of 229mTh as well.

为229mTh的研究准备一个同位素纯229Th Ion光束

A methodology is described to generate an isotopically pure 229Th ion beam in the 2+ and 3+ charge states. This ion beam enables one to investigate the ...

Demonstration of Equal-Intensity Beam Generation by Dielectric Metasurfaces

The fabrication and characterization protocol for a metasurface beam splitter, enabling equal-intensity beam generation, is demonstrated. Hydrogenated amorphous silicon (a-Si:H) is deposited on the fused silica substrate, using plasma-enhanced chemical vapor deposition (PECVD). Typical amorphous silicon deposited by evaporation causes severe optical loss, impinging the operation at visible frequencies. Hydrogen atoms inside the amorphous silicon thin film can reduce the structural defects, improving optical loss. Nanostructures of a few hundreds of nanometers are required for the operation of metasurfaces in the visible frequencies. Conventional photolithography or direct laser writing is not feasible when fabricating such small structures, due to the diffraction limit. Hence, electron beam lithography (EBL) is utilized to define a chromium (Cr) mask on the thin film. During this process, the exposed resist is developed at a cold temperature to slow down the chemical reaction and make the pattern edges sharper. Finally, a-Si:H is etched along the mask, using inductively coupled plasma&#8211;reactive ion etching (ICP-RIE). The demonstrated method is not feasible for large-scale fabrication due to the low throughput of EBL, but it can be improved upon by combining it with nanoimprint lithography. The fabricated device is characterized by a customized optical setup consisting of a laser, polarizer, lens, power meter, and charge-coupled device (CCD). By changing the laser wavelength and polarization, the diffraction properties are measured. The measured diffracted beam powers are always equal, regardless of the incident polarization, as well as wavelength.

A protocol for the fabrication and optical characterization of dielectric metasurfaces is presented. This method can be applied to the fabrication of not only beam splitters, but also of general dielectric metasurfaces, such as lenses, holograms, and optical cloaks.

电介质元表面的等强度光束生成演示

The fabrication and characterization protocol for a metasurface beam splitter, enabling equal-intensity beam generation, is demonstrated. Hydrogenated ...