Numerical Simulation of Thermal Runaway in a THz GaAs Photoconductor
Ultrafast terahertz photoconductor devices, especially photomixers, are usually limited in output power by device failure thought to be caused by excessive temperatures. Therefore, understanding of thermal breakdown is essential to the study of device reliability and failure of photoconductors.
We performed a series of simulations to determine the electronic and thermal thresholds responsible for device failures. By taking advantage of the powerful multiphysics capabilities in COMSOL Multiphysics® software, we coupled the Semiconductor Module and Heat Transfer Module to compute device properties for various bias voltages.
Beyond a maximum voltage, the presence of a positive-feedback thermal runaway effect was noted in the simulation data. It was found that the root cause of the thermal runaway is thermal ionization of the deep levels required for ultrafast recombination.
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