9.1 Introduction

The electronic and transport properties of electronic devices were reviewed in Chap. 7. These devices are usually microelectronic devices based on homojunction and heterojunction structures. Electronic devices are divided into two classes depending on their operational mode. The first class is called potential-effect devices, where the transport properties are due to carrier injections. Bipolar transistors, which include heterojunction bipolar transistors, and hot electron transistors are examples of this class of devices. Hot electron transistors include both ballistic injection devices and real-space transfer devices. The second class is called field-effect or voltage-controlled devices. Metal-oxide-semiconductor field-effect transistors (MOSFETs), homogeneous field-effect transistors, and heterostructure field-effect devices all belong to the second class. There are several variations of MOSFETs, such as semiconductor on insulator, complementary MOSFETs, n-type MOSFETs, and p-type MOSFETs. Metal-semiconductor field-effect transistors (MESFETs) and junction field-effect transistors (JFETs) are examples of homogeneous field-effect devices. An example of heterojunction field-effect devices is modulation-doped field-effect transistors (MODFETs), which are also called high electron mobility transistors (HEMTs). This chapter focuses on heterojunction devices, and thus bipolar transistors and MOSFETs will not be discussed, since they are the subject of many textbooks.

The simplest electronic device is the ohmic contact that is based on metal-semiconductor interfaces. For any electronic device to be functional, ohmic contacts are required to allow the charge carrier to move with ease in and out of the device. In other words, the current-voltage ( I- V) curve must be linear (nonrectifying) for both positive and negative...