Thermal effects on the forward characteristics of silicon p-i-n diodes at high pulse currents

When applying high pulse currents, the resulting temperature increase in the base regions of p-i-n diodes and thyristors leads to notable changes in the forward characteristics. (I) Decrease of carrier mobility noticeably increases the voltage drop across the diode and tends to limit the current density. (II) When the temperatures are sufficiently high to supply high intrinsic carrier concentrations, the temperature coefficient of the resistivity becomes negative. This can lead to current localization and destruction of the diodes.

To study these effects, the temperature of the base regions was monitored during high pulse currents using thermal i.r. emission. Indication for current limit occurs above 200°C, when the diodes are heated from room temperature. The negative temperature coefficient of the resistivity occurs at temperatures at which the intrinsic carrier concentration has reached the same order of magnitude as the injected carrier density. Simple theoretical treatment yields reasonably good agreement with the experimental results.