ABSTRACT

This chapter gives a historical overview of research performed on the metal-induced crystallization (MIC) process. The MIC temperatures and behaviors for a wide range of metal/amorphous semiconductor systems, as reported in the literature (data obtained using different experimental approaches), have been summarized and tabulated. The development of an understanding of the mechanisms controlling MIC, and related phenomena such as layer exchange, as well as the technological applications of these processes have been sketched as an introduction to later chapters of this book.

1.1 A Brief History of Metal-Induced CrystallizationIn 1969, Oki et al. [1] observed that amorphous Ge (a-Ge) crystallizes at surprisingly low temperatures when it is in contact with a metal such as Al, Ag, Au, Cu, or Sn. Shortly thereafter, Bosnell and Voisey reported that such decreased crystallization temperatures also occur for amorphous Si (a-Si) in contact with a metal [2]. In both studies, the amorphous semiconductors (and the metals) were prepared by vacuum evaporation and an electron diffraction technique was used to detect the occurrence of crystallization. Thereafter, more detailed electron microscopic investigations of this striking effect were carried out by Herd et al. [3] and Ottaviani et al. [4-6], and this phenomenon was named metal-contact-induced crystallization [3], nowadays usually referred to as metal-induced crystallization (MIC). The MIC process was found to be associated with intermixing of the semiconductor and the metal, and small crystallites of Si or Ge could indeed be found to have formed in the metal [3-6]. On the basis of these observations, the MIC effect was interpreted as the result of initial dissolution of the semiconductor into the metal, followed by precipitation of the crystalline semiconductor out of the metal matrix [4-6]. An important role of fast atomic transport along the metal/semiconductor interface was indicated in these early studies [3-6]. A very different interpretation of the MIC effect was given by Brodsky and Turnbull [7], who instead suggested that MIC would be mediated by the formation of a low-temperature eutectic melt caused by lowering of the binary eutectic temperature when one of the two components (i.e., the semiconductor) is amorphous. As compared to the above-described early interpretative efforts, understanding of the MIC process was greatly advanced in the early 1990s by the application of in situ heating transmission electron microscopy (TEM) techniques, which were developed in the late 1980s. By employing in situ heating high-resolution transmission electron microscopy (HRTEM), the MIC process in layered structures of simple eutectic metal semiconductor systems, such as crystalline Al (c-Al)/a-Si [8], crystalline Ag (c-Ag)/a-Ge [9], and c-Ag/a-Si [10], was investigated. It was shown that the MIC process does not involve the formation of any liquid phase: it is a fully solid-state