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

本计画的目的在于阐明磊晶成长条件如基板温度与环境气体对基板表面的影响。通过测量超高真空下液态金属在表面的接触角，研究了润湿张力.接触角可以在UHV和氢气中在20至550摄氏度的衬底温度下测量。2.提出了一种新的Ga液滴与GaAs衬底接触的机制。我们没有将Ga滴在GaAs上，而是使GaAs与Ga液滴接触。这使得容易去除Ga液滴的表面氧化物，并且可以在一个抽空循环中在两个以上的温度下进行测量，尽管我们使用一个Ga液滴进行一次测量。纯水处理的GaAs表面的接触角，由水氧化，显示140度常数，虽然在UHV衬底温度从20到550摄氏度增加。在半净溶液和低溶解氧纯水处理的GaAs中，表面氧化物被还原后，在超高压下，随着温度的升高，接触角从140度减小到120度.在氢气中，随着温度的升高，清洗后的GaAs表面在半清洁中的接触角从130度减小到90度.实验表明，GaAs衬底的润湿张力对外延生长Ge薄膜的电学特性有很大的影响.最好使用经半清洁等处理的GaAs，超高真空接触角测量是研究低温外延生长条件的一种很有前途的方法。

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.