Heterostructure Electronic Devices

Abstract

AbstractCompound semiconductors are excellent candidates for high-speed device applications due to their high electron mobility, the ability to form heterostructures, and the availability of semi-insulating substrates. However, the multicomponent nature and the lack of robust native oxides make the fabrication of compound semiconductor-based metal-oxide-semiconductor field-effect transistors (MOSFETs) an extremely difficult task. Instead, GaAs-based metal–semiconductor field-effect transistors (MESFET) were developed initially. A MESFET utilizes a metal–semiconductor Schottky barrier to replace the MOS gate structure. The charge carriers in the active region (channel) are separated spatially from the control (gate) electrode by a depletion layer formed on the semiconductor surface. Nevertheless, due to the nature of the Schottky barrier and high electron mobility, only n-channel MESFETs were studied and the devices are leaky at high positive biases. With the advancements of epitaxial growth technology and new device concepts, efficient advanced devices were developed. Among many three-terminal device structures, the modulation-doped field-effect transistor (MODFET), or high-electron-mobility transistor (HEMT), and the heterojunction bipolar transistor (HBT) are the most widely used high-speed devices. In this chapter, after a brief review of the MESFET, the development and working principles of HEMTs and HBTs are discussed in great detail. Then the key concepts of achieving an oxide-semiconductor interface with low interface state density necessary for the fabrication of high performance III–V MOSFETs are discussed.