"IN-SITU"OBSERVATION OF EPITAXIAL GROWTH SURFACE BY CONTACT ANGLE MEASUREMENT IN ULTRA-HIGH VACUUM

本项目的目的是阐明外延生长条件，如衬底温度和环境气体对衬底表面的影响。测量了超高真空(UHV)中液态金属在表面的接触角，以研究润湿张力。在超高压和氢气中，接触角可以在20-550摄氏度的衬底温度下测量。我们开发了一种新的机制来接触镓液滴和砷化镓衬底。我们没有在GaAs上滴下Ga，而是使GaAs与Ga液滴接触。这使得我们很容易去除镓液滴的表面氧化物，并且可以在一个真空循环中在两个以上的温度下测量，尽管我们只使用一个镓液滴进行一次测量。经水处理的纯水处理的砷化镓表面，在紫外光下衬底温度从20℃升高到550℃时，接触角保持140度恒定。表面氧化物减少的半净溶液和/或低溶氧纯水处理后的GaAs的接触角随着温度的升高从140度下降到120度。在氢气中，随着温度的升高，清洗后的GaAs表面的接触角从130度下降到90度。从实验上阐明了在GaAs衬底上外延生长的Ge薄膜的电学特性受衬底润湿程度的影响。Ge的低温外延生长宜采用经半清洁等处理的GaAs，并在氢气中生长。超高真空下的接触角测量是探索低温外延最佳生长条件的一种有前途的技术。

The purpose of this project is to clarify the effects of epitaxial growth conditions such as substrate temperature and ambient gas on substrate surface. The contact angle of liquid metal on the surface in ultra-high vacuum (UHV) are measured to study the wetting tension.1. The contact angle can be measured at the substrate temperature from 20 to 550 degree C in UHV and in hydrogen.2. We developed a new mechanics to contact Ga droplet and GaAs substrate. We did not drop Ga on GaAs, but GaAs was brought into contact with Ga droplet. This makes easy to remove surface oxide of Ga droplet and possible to measure at more than two temperatures at one evacuation cycle though we use one Ga droplet for one measurement.3. The contact angle of pure water-treated GaAs surface, oxidized by the water, showed 140 degree constant, though the substrate temperature increased from 20 to 550 degree C in UHV.4. The contact angles of cleaned GaAs in semicoclean solution and/or low dissolved oxygen pure water-treated GaAs, which surface oxide were reduced, decreased from 140 to 120 degree, as the temperature increased in UHV.5. The contact angle of cleaned GaAs surface in semicoclean decreased from 130 to 90 degree, as the temperature increased in hydrogen.6. It was clarified experimentally that wetting tension of GaAs substrate, which showed the grade of wetting, influence on the electrical characterization of epitaxially grown Ge films on the GaAs.7. It is better to use GaAs treated with semicoclean etc., and to grow in hydrogen for low temperature epitaxial growth of Ge on GaAs.Contact angle measurement in UHV is one of the promising technique to investigate the best growth condition for low temperature epitaxy.