Unit 4

MICROWAVE SOLID STATE DEVICES

RIDLEY WATKINS HILSUM THEORY

The separation between the bottom of the lower valley and the bottom of upper valley must be greater than 0.026 eV.

Electrons in the lower valley must have high mobility,small effective mass, low density where as the upper valley must have low mobility,large effective mass and high density

Separation energy between the valleys must be smaller than the gap energy b/w conduction & valence bands

Two most useful semiconductors Si,Ge do not meet all these criteria So GaAs,InP,CdTe do satisty these

criteria

GUNN DIODE

GUNN DIODE

Eq-ckt

a)fL=10^7cm/sec,b) fL<10^7cm/sec,c) fL>2*10^7cm/sec

LSA Mode

Oscillations builds up when the –ve resistance of the gunn diode equals to the load resistance.

The peak to peak amplitude of the oscillations are approximately equal to the voltage range in the –ve resistance region

Impatt Diode(impact ionization avalanche transit time)

Trapatt Diode(trapped plasma avalanche triggered transit time)

Tunnel diode