Optical characterization of impact ionization in flip-chip-bonded InP-based high electron mobility transistors

Impact ionization in flip-chip-bonded InP-based high electron mobility tran sistors (HEMTs) with 0.1-mu m gates is examined by measuring their electrol uminescence (EL). We extract quantities proportional to the concentration o f impact-ionization-induced holes at the source edge and the impact ionizat ion probability of a single electron for a wide range of bias voltages. The lateral extension of the high-field region at the drain edge, where the im pact ionization occurs, is also estimated. Furthermore, the EL signal from each of two neighboring HEMTs separated by 20 mu m is clearly resolved in t he spatial distribution measurement, which suggests that the present method is also applicable for characterizing individual devices in actual ICs.