Off-state breakdown of GaAs PHEMTs: review and new data

This paper reviews the literature dealing with off-state gate-drain breakdown in MESFET and HEMT structures, with particular emphasis on GaAs PHEMTs, in terms of: 1) the physics of the breakdown phenomenon; 2) the breakdown walkout effect; 3) the impact of design and process choices on the breakdown behavior; and 4) the experimental techniques used for breakdown characterization. A thorough temperature-dependent breakdown characterization of commercial PHEMTs is also shown and discussed. It is found that different physical mechanisms may dominate the gate-drain leakage depending on the reverse bias and temperature range considered, and the particular PHEMT technology. The main results shown here tell us the following. 1) The breakdown voltages are decreasing functions of temperature between room temperature and 160°C. 2) Between room temperature and 90-100°C, thermionic-field emission seems be dominant, with low activation energies below 0.15 eV; as a consequence, the temperature dependence of the breakdown voltage is weak. 3) Between 110°C and 160°C, higher activation energy mechanisms (possibly trap-assisted tunneling and thermionic emission over a field-dependent barrier) tend to dominate, and the temperature dependence of the breakdown voltages is stronger.