Development for liguid phase epitaxy by solvent evaporation

由于外延生长技术具有很高的便利性和生产率，因此在制造许多电子器件方面具有很高的实用价值。在这些外延技术中，液相外延生长速度快，重复性好，是最有用的外延方法之一。我们开发的溶剂蒸发外延方法简单：在衬底晶体表面涂上溶质和溶剂的固体混合物，然后通过加热使溶剂蒸发。尽管这种外延技术很简单，但目前只报道了几次外延实验，而且这项技术的发展还存在许多问题。在这项研究中，我们将该技术应用于几个氧化物系统。以氧化镁单晶的(100)面为衬底，报道了MnO、CoO、NiO简单氧化物、BSCCO系氧化物超导体和透明导电尖晶石ZNGA_2O_4的实验结果。从本研究的结果可以看出以下优势：1)方法简单。2)当实验条件确定时，外延生长可以重复进行。3)不需要进一步处理将外延层从溶液中分离出来。另一方面，也存在以下不利因素：1)溶剂材料是重要的，但有限的。2)由于加热温度较高，薄膜和衬底之间经常会发生意想不到的化学反应。3)只有当合适的生长条件急剧稳定时，才能进行均匀的外延生长。综上所述，溶剂蒸发外延实际上是制备氧化物晶体薄膜的一种重要方法。然而，也很明显，要为许多设备制作完美的薄膜仍然存在许多问题。

Because of high convenience and productivity, the epitaxial growth techniques possess high utilities for fabricating many electronic devices. The liquid phase epitaxy is one of the most useful method among these epitaxial techniques due to high growth rate and reproducibility. The solvent evaporation epitaxy, which has been developed by us, is conducted in a following simple way : a solid mixture of solute and solvent is plastered on a surface of substrate crystals and then the solvent is evaporated by heating them. Despite of the simplicity, only a few trials of this epitaxy have been reported and many points for developping the technique have remained. In this study, we applied the technique for several oxide systems. The (100) surfaces of MgO single crystals were used as a substrate and experiments on simple oxides of MnO, CoO and NiO, oxide-superconductors of the BSCCO system and a transparent conductive spinel of ZnGa_2O_4 were reported. From the results of this study, the following superior points became clear : 1) The method is simple. 2) Epitaxial growth proceeds reproductively when the experimental conditions are settled. 3) No further treatment for separating the epitaxed layers from the solutions is needed. On the other hand, the next disadvantageous points existed : 1) Solvent materials is important but limited. 2) Because of the high heating temperatures, unexpected chemical reactions often occur between films and substrates. 3) Uniform epitaxial growth proceeds only when the appropriate growth conditions are settled sharply. As a conclusion, the solvent evaporation epitaxy is actually a prominent method for preparing oxide crystal films. However, it also became clear that there remain many problems to produce perfect films for many devices.