Introduction

Research on semiconducting materials started in the early nineteenth century. Since then, many semiconductors have been investigated. Certainly the most well-known materials are Silicon Si and germanium Ge, which both belong to column IV of the periodic table of elements. While a bulk crystal of Si or Ge consists of the periodic arrangement of a single atom, other semiconductors like gallium arsenide GaAs (III-V) are built with two different elements: Ga (III) and As (V). Such composite semiconductors have electrical or optical properties that are not achievable with pure semiconductors made of only one type of atoms.

Before the bipolar transistor was invented in 1947, semiconductors were used in basically two types of electrical devices: photodiodes and rectifiers. In the nineteen fifties, germanium used to be the most frequently employed material. However, it could not be used in applications requiring weak current consumption and/or operation under high temperatures. Silicon has started overcome all other semiconductors since 1960, because it was both significantly cheaper and less power-consuming.