The Differences Between One-Dimensional and Three-Dimensional Semiconductors

The semiconductors with which we are most familiar, such as germanium and silicon, behave similarly in all three dimensions: Under most circumstances, electrons, for example, move equally well along the three crystal axes. There are, however, materials whose structure is so anisotropic that their properties as measured along one axis differ drastically from those measured in the other directions. In such materials the electrons may behave as if they were confined to move in only one or two dimensions. In particular, the quasi-one-dimensional materials have aroused a great deal of interest over the past decade. Thus, for example, a recent international conference on low-dimensional conductors at Abano Terme, Italy, in June 1984, had about 500 participants and almost as many papers discussing quasi-one-dimensional metallic, semiconducting, and superconducting materials. (As we shall see, these are for the most part the same materials under different conditions of temperature, doping or pressure.)