Thermal studies on heterostructure bipolar transistors using electroluminescence

We have studied electroluminescence (EL) emission from fully fabricated GaAs based heterostructure bipolar transistors. The EL emission occurs due to minority carrier injection into the base and collector layers. Under normal device operation, i.e. with reverse bias on the collector/base junction, collector emission does not occur since holes are not injected into this layer. In this case, only base emission is observed. When a forward bias is applied to the base/collector junction, EL from both the collector and the base is observed. The spectral characteristics of the two EL signals are different since the bandgap of the heavily p-doped base is smaller than that of the lightly n-doped collector. Since the bandgap depends strongly on temperature, the spectral characteristics are used to determine the heating of the HBT due to power dissipation.