Negative Electron Affinity Photocathodes on Non- (001) Surfaces

负电子亲和势(NEA)光电阴极在很宽的波长范围内具有很高的灵敏度，具有重要的实用价值。人们强烈要求提高灵敏度和延长使用寿命。在本研究项目中，研究了在高折射率表面形成的新型NEA光电阴极和NEA表面的结构。除了通常用于NEA GaAs光阴极的(001)面外，还在(111)A和(311)A面上制备了GaAs光阴极。结果发现，在热清洗过程中存在一个临界温度，并且在非(001)晶面上获得较高的灵敏度。为了研究NEA衬底的表面结构，我们在伦敦大学帝国理工学院的MBE-STM联合系统上进行了分子束外延和非原位生长NEA衬底的原子级扫描隧道显微镜(STM)成像。在此基础上，利用自制的MBE-STM系统清晰地观察到了(111)A和(311)A上的梯形结构特征。阐明…的表面结构和近红外光谱机理除了在高折射率表面的NBA光电阴极方面的合作外，我们还发现了两个研究所独立研究的光电子器件制作方面的共同兴趣，特别是具有量子结构的半导体激光器。作为光电子器件制备的基础研究，我们用分子束外延(MBE)方法生长了InGaAs/GaAs多量子阱(MQW)结构。在V/III=3.8时生长的样品具有最大的荧光强度。在帝国理工学院用STM-MBE组合系统对我们的图案化衬底的生长和评估表明，在预图案化的衬底上进行原子尺度的原位观察是有潜力的。我们还展示了MBB的生长在正方形台面上形成了金字塔结构。我们认为，上述结果是光电器件应用的第一步，值得进一步推广。乔伊斯教授建议我们扩大合作活动。较少

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