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 transistors (HEMTs) with 0.1-μm gates is examined by measuring their electroluminescence (EL). We extract quantities proportional to the concentration of impact-ionization-induced holes at the source edge and the impact ionization 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 impact ionization occurs, is also estimated. Furthermore, the EL signal from each of two neighboring HEMTs separated by 20 μm is clearly resolved in the spatial distribution measurement, which suggests that the present method is also applicable for characterizing individual devices in actual ICs.