Instrument to identify defects and impurities in wide band gap semiconductors via excited states

研究人员建议开发一种新的仪器来测量宽带隙半导体中缺陷的电学性质。目前最重要的宽禁带材料是由元素周期表第三族金属和氮组成的化合物，如GaN和InGaN。这些被称为III-N材料。它们被用来制造低能照明、激光以及高效的射频和大功率晶体管。从材料的性质来看，今天这一代设备的功能并不像看起来可能的那样好，目前的功能和性能是有限的。LED和激光(除蓝色以外)的发光效率低于预期，而且在晶体管的情况下，性能的几个方面也不尽如人意。这至少部分是由于组件材料和器件中存在缺陷。使用现有技术很难识别这些缺陷。它们可能是由于晶体生长或在器件制造过程中引入的晶格中的杂质或缺陷造成的。曼彻斯特的研究小组在解决其他材料(如砷化镓和硅)的缺陷问题方面拥有30多年的经验。由这些材料制成的设备通过大规模生产的电子和通信技术已经给社会带来了革命性的变化。测量、了解和控制缺陷，特别是电活性缺陷的能力，在这一巨大的技术成就中发挥了重要作用，从曼彻斯特设计、开发和许可的仪器在这方面发挥了作用。对于III-N材料，检测缺陷和量化它们的性质要困难得多，目前还没有技术可以观察所有的带隙并量化导致III-N器件退化的复合路径和陷阱中心。新仪器的特点是使用可调谐半导体激光器的子带隙光来产生缺陷的激发态。然后，载流子从激发态热电离到半导体带上。由于光激发激发了束缚到束缚的跃迁，因此可以获得精细的线谱，这是缺陷种类及其在晶格中位置的指纹。在存在许多缺陷的情况下，将使用我们现有的拉普拉斯DLTS处理来分离发射速率。可以使用为DLTS和LDLTS的变体开发的方法来获得复合和捕获参数。我们的一个项目合作伙伴(加利福尼亚州的圣巴巴拉大学)将进行理论研究，旨在将激发态光谱与化学物种和/或缺陷的结构联系起来，以期进行普遍鉴定，而不是使用与先前获得的光谱的相关性。仪器开发是对许多英国大学目前正在进行的开发III-N材料和器件的EPSRC合同的补充。在仪器开发的初始阶段，与剑桥和格拉斯哥牵头的财团就测试材料和电力设备的合作进行了谈判。随着项目的进展，这一范围将扩大到包括其他群体。业界对该项目的兴趣已经导致了III-N材料、LED、GaN功率器件和仪器制造领域的五家公司的大力支持。其中四家是总部设在英国的。成功完成这项合同对社会的潜在好处是巨大的，它促进了国内照明的更大改进，并使III-N材料的新应用得以开发，例如在高效短波UV GaN LED中。它们可以用于廉价、低维护的饮用水消毒，这是发展中国家迫切关注的问题。

The researchers propose to develop a new instrument to measure the electrical properties of defects in wide band gap semiconductors. The most important wide gap materials at the present time are compounds made from metals from group III of the periodic table and nitrogen such as GaN and InGaN. These are referred to as III-N materials. They are used to make low energy lighting, LASERs and efficient RF and high power transistors. Today's generation of these devices does not function as well as would seem possible from the properties of the materials and at the present time functionality and performance is limited. LEDs and LASERs (other than blue) are less efficient at generating light than expected and in the case of the transistors several aspects of performance are less than desirable. This is due, at least in part, to the presence of defects in the component materials and devices. These defects are difficult to identify using existing techniques. They may be due to impurities or imperfections in the crystal lattice resulting from the crystal growth or introduced during the device manufacturing process. The research group at Manchester have over thirty years of experience in solving defect problems in other materials such as GaAs and Si. Devices made from these materials have revolutionized society through mass produced electronics and communication technologies. The ability to measure, understand and control defects, particularly electrically active defects, has played a major role in this immense technological achievement and instruments devised, developed and licensed from Manchester have played a role in this. In the case of the III-N materials detecting defects and quantifying their properties is much more difficult and no technique exists at the moment which can look at all the band gap and quantify the recombination paths and trapping centres which degrade III-N devices.The defining feature of the new instrument is that it uses sub-band gap light from tunable semiconductor LASERs to create excited states of the defects. Carriers are then thermally ionised to the semiconductor bands from the excited states. Because the optical excitation stimulates a bound to bound transition, a fine line spectrum can be obtained which is a fingerprint of the defect species and its location in the lattice. In the case of many defects being present, the emission rates will be separated using our existing Laplace DLTS processing. Recombination and trapping parameters can be obtained using the methodologies developed for variants of DLTS and LDLTS. One of our project partners (Santa Barbara University in California) will undertake theoretical studies aimed at associating the excited state spectra with chemical species and/or the structure of the defect with a view to generalized identification rather than using correlation with previously obtained spectra.The instrument development is complementary to the EPSRC contracts currently in progress at many UK universities for the development of III-N materials and devices. In the initial phase of the instrument development, collaborations with consortia led by Cambridge and Glasgow for testing materials and power devices have been negotiated. This will be broadened to embrace other groups as the project progresses. Industrial interest in the project has resulted in strong support from five companies in the field of manufacture of III-N materials, LEDs, GaN power devices and instrumentation. Four of these are UK based. The potential benefits to society of a successful completion of this contract are enormous in facilitating greater improvements in domestic lighting and enabling new applications of the III-N materials to be developed for example in efficient short wavelength UV GaN LEDs. These could be used in cheap low maintenance drinking water sterilization, a pressing concern in the developing world.