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

该项目的目的是澄清外延生长条件，如衬底温度和环境气体对衬底表面的影响。通过测量金属液在超高真空（UHV）条件下表面的接触角，研究了金属液的润湿张力。接触角可以在基片温度从20到550℃的特高压和氢中测量。我们开发了一种新的砷化镓液滴与砷化镓衬底接触的机制。我们没有将Ga滴在GaAs上，而是将GaAs与Ga滴接触。这使得易于去除Ga液滴的表面氧化物，并且可以在一个疏散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。纯水处理的砷化镓表面被水氧化后，接触角保持在140度恒定，而基片温度在uhv下从20℃升高到550℃。在UHV.5中，随着温度的升高，表面氧化物减少的半净溶液和/或低溶解氧纯水处理的GaAs的接触角从140度降低到120度。5 .随着氢中温度的升高，半净净化后的GaAs表面接触角由130°减小到90°。实验表明，表征GaAs衬底润湿程度的润湿张力对GaAs上外延生长的Ge薄膜的电学特性有影响。在GaAs上低温外延生长，最好采用半洁净等处理过的GaAs，并在氢气中生长。超高压接触角测量是研究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.