Gallium Arsenide (GaAs) Devices

Gallium Arsenide (GaAs) Devices

In this article, the first and second generation types of Gallium Arsenide (GaAs) devices are explained.

During the last few years a number of different devices have been developed. MESFET was regarded as one of the earliest type of GaAs devices. The so-called ‘first generation’ of GaAs devices includes:

• Depletion-mode metal semiconductor field-effect transistor [D-MESFET]
• Enhancement-mode metal-semiconductor field-effect transistor [E-MESFET]
• Enhancement-mode junction field-effect transistor [E-JFET] and
• Complementary enhancement-mode junction field-effect transistor [CE-JFET]

The First generation GaAs gates have shown switching delays to as low as 70 to 80 psec for a power dissipation in the order of 1.5 mW to 150 microW.

There are other more sophisticated/second generation’ devices such as:

• High electron mobility transistor [HEMT]
• Hetero-junction bipolar transistor [HBT]

Electron mobility in second generation transistors can be up to five times greater than in the first generation. As a result of this boom, very fast devices are possible.

However, in the following posts we will concentrate on establishing some of the fundamental principles of GaAs design for the first generation devices only, particularly the predominant MESFETs, which are now at a stage of development that enables them to be used in very fast VLSI systems.