Introduction

Abstract

Electron devices using the rectifying properties of compound semiconductors have been utilised from the very early stages of the development of electromagnetic waves as a means of communication. Natural crystals of galena (lead sulphide) were used in point-contact detectors as early as in 1904 [1.1]. However, as the technology of preparation and purification of semiconductors advanced, interest was shifted to the elemental semiconductors, silicon and germanium. Subsequent point-contact detectors, which continued to be used as microwave mixers and detectors even after the advent of vacuum tubes, were mostly made with silicon. Interest in elemental semiconductors was also greatly enhanced when transistor action was discovered in germanium in 1948 [1.2]. Silicon soon replaced germanium in transistors because of its greater thermal stability. As a result of the invention of the transistor, germanium and silicon became the two most intensely studied semiconductors in course of the next few years.