SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

416 CHAPTER 8. FIELD EFFECT TRANSISTORS

1 10 102 103 104

10

102

103

Diamond

Ge

GaAs

Si InP

SiC

M

AXIMUM ALLOWABLE VOLTAGE

(V)

MAXIMUM FREQUENCY fT(GHz)

Figure 8.41: Plot of the maximum operating voltage for transistors made of selected semiconduc-
tors as a function of estimatedfτ.Thefτestimates are based on the steady-state velocity-field
curve for each material. (After M. W. Geis, N. N. Efremow, and D. D. Rathman, “Summary
Abstract: Device Applications of Diamond,”J.Vac.Sci.Technol.A6, 1953 (1988).)

which is purely dependent on the material parameters. So, the transistorfτandVbrhave to be
traded against each other, with extended drift regions giving high breakdown voltages but low
fτand thin drift regions giving low breakdown voltages but highfτ.

8.8.3 Classes of operation of transistor power amplifiers and necessary de-

vice characteristics

The configuration of the uses of transistor amplifiers in say transmitter(power) applications
are called classes and determined by one or more of the following criterion:

1. where the device is biased


2. what load-line the device sees


3. whether the active device is operated as an amplifier or a switch

Though the number of classes in existence is far too many to be described here in detail, we will
briefly describe the class-A, and class-AB/B operations and highlight their performance with