21.5 Applications and Special Diode Devices
587
Fig. 21.77 Comparison of
tunneling characteristic
(room temperature) of
diodes based on Ge, GaSb
and GaAs. Peak-to-valley
ratios are 8 (Ge) and 12
(GaSb, GaAs). Adapted
from [574]
(a)
(b)
Fig. 21.78 a Current traces upon excitation of a 25 µm thick piece of n-type GaAs with a voltage pulse (amplitude 16 V
and duration 10 ns). The upper trace is an expanded view of the lower trace. The oscillation period is 4.5 GHz. Adapted
from [134]. b Image of packaged Gunn diode (Linwave DC1276G-T for 26–40 GHz), outer diameter 3 mm
current minimum is at a voltage V = V n + V p > 0. The thermal current is the normal diode diffusion
current (Fig. 21.75e). Therefore, a minimum is present in the I –V characteristic. The excess current
is due to inelastic tunneling processes through states in the band gap and causes the minimum to not
drop down to almost zero current.
The peak (V p , I p ) and valley (V v , I v ) structure of the characteristic leads to a region of negative
differential resistance (NDR). I p /I v is termed the peak-to-valley ratio (Fig. 21.77). Peak-to-valley ratios
of 8 (Ge), 12 (GaSb, GaAs), 4 (Si), 5 (InP) or 2 (InAs) have been reported (all at room temperature).
21.5.10 Backward Diodes
When the doping in a tunneling diode is nearly or not quite degenerate, the peak-to-valley ratio can be
very small. Then the tunnel current flows mostly in the reverse direction (low resistance) and the forward
direction has a higher resistance (with or without the NDR regime). Such diodes are called backward
diodes. Since there is no minority charge carrier storage, such diodes are useful for high-frequency
applications.
587
Fig. 21.77 Comparison of
tunneling characteristic
(room temperature) of
diodes based on Ge, GaSb
and GaAs. Peak-to-valley
ratios are 8 (Ge) and 12
(GaSb, GaAs). Adapted
from [574]
(a)
(b)
Fig. 21.78 a Current traces upon excitation of a 25 µm thick piece of n-type GaAs with a voltage pulse (amplitude 16 V
and duration 10 ns). The upper trace is an expanded view of the lower trace. The oscillation period is 4.5 GHz. Adapted
from [134]. b Image of packaged Gunn diode (Linwave DC1276G-T for 26–40 GHz), outer diameter 3 mm
current minimum is at a voltage V = V n + V p > 0. The thermal current is the normal diode diffusion
current (Fig. 21.75e). Therefore, a minimum is present in the I –V characteristic. The excess current
is due to inelastic tunneling processes through states in the band gap and causes the minimum to not
drop down to almost zero current.
The peak (V p , I p ) and valley (V v , I v ) structure of the characteristic leads to a region of negative
differential resistance (NDR). I p /I v is termed the peak-to-valley ratio (Fig. 21.77). Peak-to-valley ratios
of 8 (Ge), 12 (GaSb, GaAs), 4 (Si), 5 (InP) or 2 (InAs) have been reported (all at room temperature).
21.5.10 Backward Diodes
When the doping in a tunneling diode is nearly or not quite degenerate, the peak-to-valley ratio can be
very small. Then the tunnel current flows mostly in the reverse direction (low resistance) and the forward
direction has a higher resistance (with or without the NDR regime). Such diodes are called backward
diodes. Since there is no minority charge carrier storage, such diodes are useful for high-frequency
applications.