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Advanced Materials

Advanced materials for GaAs Microwave Devices

Authors

  • Dr. Robin S. Smith,

    Corresponding author
    1. GEC-Marconi Materials Technology Ltd. Caswell, Towcester, Northants NN12 8EQ (UK)
    • GEC-Marconi Materials Technology Ltd. Caswell, Towcester, Northants NN12 8EQ (UK)
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    • Received his Ph.D. in 1968 from Reading University for work on infrared absorption by local mode vibrations of defect complexes in silicon. He then joined Plessey Caswell, where he worked on diffusion in silicon and GaAs and gas-phase epitaxy of InP for microwave devices. From there he moved to the Fraunhofer Institute for Applied Solid State Physics in Freiburg, FRG, where he set up a gas-phase epitaxy and MBE facility. His work involved the growth of GaAs structures for mixer and Gunn diodes, doping experiments including the rare earths erhium and ytterbium in GaAs and single crystal iron, and ErAs and YbAs on GaAs. He then moved to GEC Hirst Research Centre and then 10 Caswell again, where he is in charge of the MBE group.

  • Dr. Ian G. Eddison

    Corresponding author
    1. GEC-Marconi Materials Technology Ltd. Caswell, Towcester, Northants NN12 8EQ (UK)
    • GEC-Marconi Materials Technology Ltd. Caswell, Towcester, Northants NN12 8EQ (UK)
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    • Received his Ph.D. in 1978 from Leeds University for work on GaAs microwave oscillator devices. In 1976 he joined Plessey Caswell, where he worked on GaAs oscillators for millimeter wave frequencies, and InP devices operating up to 100 GHz. In 1981 he moved into the GaAs integrated circuit section to work on broadband, on-wafer characterization of GuAs discrete devices and ICs. Following the acquisition of Caswell by GEC-Marconi he took responsibility for both technology and circuit design R and D as department manager, where his interests range from ion implantation and MBE growth of compound semiconductors, through MESFET and HEMT process technology to advanced circuit design and CAD technique development.


  • The authors would like to thank GEC-Marconi for supporting this work and their colleagues at GMMT Caswell whose contributions and encouragement have helped to make this work a success.

Abstract

A number of III–V compound semiconductors have higher electron mobilities and peak electron velocities than silicon. This makes these materials attractive for use in high-frequency applications. However, the use of these materials was delayed for a number of years by the fact that, most of these compounds such as GaAs lack a stable native Oxide and display a large interface trap density at the junction with other materials. These problems were overcome in the early 1960s by the development of the MESFET (metal semiconductor FET) where the control electrode was formed; by a metal Schottky contact directly onto the GaAs surface. Early devices were fabricated in epitaxial conducting layers deposited, by for example vapor phase epitaxy, onto GaAs substrates. As the quality of these substrates improved, the conducting layers were formed by implantation of silicon ions directly into the substrate surface. The requirement for devices working at even higher frequencies has necessitated the move from implanted MESFETs to more complicated multi-layer heterostructures, for devices such as HEMTs (high electron mobility transistors) and HBTs (heterojunction bipolar transistors), which can only be produced using epitaxial techniques. In this article the technique of ion-implantation and molecular beam epitaxy are described together with a description of HEMTs and HBTs.

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