Negative Electron Affinity Photocathodes on Non- (001) Surfaces

负电子亲和光电阴极在宽波长范围内具有很高的灵敏度，具有重要的应用价值。人们强烈要求提高灵敏度和寿命。本课题研究了在高折射率表面上形成的新型NEA光电阴极及其表面结构。除了通常用于NEA GaAs光电阴极的（001）表面外，还可以在（111）A和（311）A表面上制造GaAs光电阴极。因此，在热清洗过程中发现了一个临界温度，并且在非（001）表面上获得了更高的灵敏度。为了研究NEA衬底的表面结构、MBE生长和非原位STM原子尺度成像，在伦敦大学帝国理工学院使用MBE-STM联合系统进行了MBE-STM原子尺度成像。在经验的基础上，用自制的MBE-STM系统对（111）A和（311）A的特征阶地构造进行了清晰的观测。澄清其表面结构和NEA机理将有助于进一步改进NBA光电阴极。除了在高折射率表面上的NBA光电阴极的合作外，我们还发现了双方在光电器件制造方面的共同兴趣，特别是具有量子结构的半导体激光器。作为光电器件制造的基础研究，我们利用分子束外延（MBE）生长InGaAs/GaAs多量子阱（MQW）结构。在V/III = 3.8条件下生长的样品PL强度最大。帝国理工学院的STM-MBE联合系统对我们的图像化基底的生长和评价表明了在预图像化基底上进行原子尺度原位观察的潜力。我们还展示了MBB的生长在方形台地上形成的金字塔结构。我们认为，上述结果是光电器件应用的第一步，值得进一步发展。乔伊斯教授建议我们扩大合作活动。少

Negative electron affinity (NEA) photocathodes have high sensitivity in a wide range of wavelength, and are practically Important. There are strong demands for sensitivity and lifetime improvements. In this research project, new NEA photocathode formed on high index surfaces and structure of the NEA surface are examined. In addition to (001) surface conventionally used for NEA GaAs photocathodes, GaAs photocathodes are fabricated on (111)A and (311)A surfaces. As a result, a critical temperature is found in heat cleaning process, and higher sensitivity is obtained on non-(001) surfaces. In order to investigate the surface structure of NEA substrates, growth by MBE and ex situ, atomic scale imaging by STM are carried out using MBE-STM combined system in Imperial College, University of London. Based on the experience, the characteristic terrace structures on (111)A and (311)A are clearly observed by our own made MBE-STM system. Clarification of the surface structure and NEA mechanism wou … More ld contribute to further improvements of NBA photocathodes.In addition to the collaboration on NBA photocathodes on high index surfaces, we found out common interest on opto-electronic device fabrication, which has been studied independently in both institutes, especially semiconductor laser with quantum structure. As a basic research of opto-electronic device fabrication, we have grown InGaAs/GaAs multi quantum well (MQW) structure using molecular beam epitaxy (MBE). The maximum PL intensity is obtained for the sample grown under V/III = 3.8. Growth and evaluation on our patterned susbstares by STM-MBE combined system In Imperial College indicates potentialities of the atomic scale In-situ observation on prepatterned substrates. We have also shown the formation of pyramid structures on the square mesa by the growth of MBB.The above mentioned results, we believe, are the first step for opto-electronic device application and worth carrying a stage further. Professor Joyce have suggested us to extend our collaborative activities. Less