TABLE OF CONTENTS Schottky contact is the term used to describe metal/semiconductor interfaces that display rectifying or diode-like behaviour. The material presented in this chapter will enable the reader to understand the basic physics of Schottky contacts, methods of forming them and ways that they form gate contacts to GaAs FETs.
The physics of Schottky contacts and their interfacial properties are given in Section 7.2. Their formation and electrical testing are discussed in Sections 7.3 and 7.4, respectively. Reliability is discussed in Section 7.5.
The physical description of a Schottky contact begins in a similar way to the description of the metal/semiconductor interface for ohmic contacts in Section 6.2. Ga or As atoms have tetrahedral symmetry in the GaAs semiconductor. Each Ga atom is surrounded by four equivalent As atoms, i.e. equally spaced, equal bond lengths, equal bond angle (109.5 ). Each As atom can be described in the same way. At a free surface, the atoms lose their four-fold bonding to other semiconductor atoms, which results in unpaired electrons. The energy of these unpaired electrons is higher than that for a fully formed bond. As a result, the overall energy level can be reduced if the surface atoms rearrange themselves and form new bonds with each other (Section 3.3.1). At an interface with a metal, similar atomic rearrangements happen, but with new bonds with metal atoms also being possible. In addition, defect structures such as missing bonds formed...
