Investigation of the lateral turn-on process of thyristors with an epitaxial p-base

In this paper, the effect of the p-base doping concentration N
A
on the spreading velocity v
s
in power thyristors is examined. Chemical vapor deposition (CVD) techniques are used to produce the p-base layer, in order to change the p-base doping concentration and thickness independently. The results show a large reduction of v
s
with growing p-base doping concentration. At a doping concentration higher than 5 × 10
¹⁶
/cm
³
the spreading velocity follows a power law with an exponent of -0,9. The introduction of a sandwiched low-doped player between the p
⁺
-base and the n-emitter slows down the plasma propagation. The decrease of v
s
, in both cases, is attributed to the reduction of the current gain β
2
of the n-p-n transistor with doping concentration. In order to explain this behavior, a simple expression for the spreading velocity is derived, which relates the spreading velocity to the time constant of current rise t
r
and consequently to the feedback loop gain (β
1
β
2
) of the two transistor components. In this derivation, only the lateral drift current in the p-base is taken into account. It was found that v
s
is given by
v_{s} \sim 1/t_{r} \sim \ln \beta_{1}\beta_{2}
, in good agreement with the experiment.