Efficiency limitation by transverse instability in Si IMPATT diodes

Measurements of large-signal impedance, ac voltage and dc voltage V
0
versus dc current I
0
on Si p-n-n
⁺
IMPATT diodes in pulse operation (80 ns) suggest that the efficiency of Si IMPATT diodes is limited by instability effects causing a splitup into regions with different current densities. The effect is explained by considering the I
0
-V
0
curves at constant ac voltage. These can be S-shaped owing to impact ionization in the drift region.