A Gunn diode is a form of diode that consists of only n-doped semiconductor material and exhibits negative differential resistance. It operates by transferring electrons from a region of high electron mobility to a region of low mobility under the influence of an increasing electric field. This causes the overall drift velocity of electrons to decrease with increasing field and enables oscillations. Gunn diodes are commonly used as microwave sources in applications such as radars and intrusion alarms, with gallium arsenide diodes operating up to 200 GHz and gallium nitride diodes reaching as high as 3 THz.

2. Gunn Diode
 A Gunn diode is also known as a transferred electron device (TED).
 Phenomenon was observed by J.B. Gunn in 1963
 It is a form of diode used in high-frequency electronics.
 It consists only of n-doped semiconductor material, whereas most diodes consist of both
P and N-doped regions. In practice, a Gunn diode has a region of negative differential
resistance.
 Gallium Arsenide Gunn Diodes are made for frequencies up to 200GHz whereas
Gallium Nitride can reach upto 3THz.
 Electric field ε across the n type Ga As sample , the drift velocity v of carriers
inside the semiconductor .
Differential mobility dv / dε = -ve
2

3. 3
 In N type Ga As === carrier electrons in lowest energy level of Conduction Band
 Here, Electron effective mass is small,
 Mobility μ1 is high ===8000cm2/volt sec
 Applied Electric field = small, the drift velocity of the carrier is given by
v = μ1 ε
 Applied Electric field increased
 Electron energy increases (energetic electrons = hot electrons)
 It transferred to the CB region where effective mass is high and
mobility is small(200 cm2/volt sec)
 n1 = number density of electrons with mobility μ1
 n2 = number density of electrons with mobility μ2
 Average drift velocity v = ε
μ1 n1 + μ2 n2
n1 + n2
Gunn Diode

4. Gunn Diode
 Electron transfer from high mobility state to low mobility state, average drift velocity
 Final Drift velocity ====== v = μ2 ε , slowly with electric field
 Due to the presence of –ve differential mobility, GaAs used for generation of
microwaves
 GaAs sample with two terminal = Gunn diodes
 Oscillators constructed using N – Ga As diodes = Gunn oscillators
 -ve differential mobility = transferred of electrons == oscillator also called TEO
 Advantages & application
 Oscillator using Gunn diodes produce microwave oscillation with less noise
than IMPATT diodes. It converting microwave frequency range from 1 to 100
GHz
 Used as microwave sources in radars, intrusion alarms and in laboratory for
microwave experiments. 4