Factors limiting the maximum operating voltage of microwave devices

The operating voltage of advanced microwave devices is currently limited by impact-ionization and breakdown effects. An extended study of the effects of hot carriers on the breakdown behavior and reliability of GaAs-based and InP-based HEMTs (high electron mobility transistors) has been carried out by means of pulsed measurements, electroluminescence spectroscopy and microscopy and Monte Carlo simulations. We show that the parasitic bipolar effect, which explains kink effects in HEMTs, can also induce regenerative phenomena eventually leading to on-state breakdown. Results concerning the effects of hot carrier aging on GaAs-based and InP-based HEMTs are summarized.