Unipolar devices (e.g., MOSFET, Schottky diode) conduct via majority carriers only, leading to a positive temperature coefficient of resistance. Bipolar devices (e.g., BJT, IGBT, p-i-n diode) inject minority carriers into the drift region during forward conduction. This creates a plasma of electrons and holes, dramatically reducing the on-resistance (the conductivity modulation effect). The penalty is stored charge, causing a reverse recovery current during switching.
The industry is shifting from Silicon to Wide Bandgap (WBG) materials (SiC and GaN). This shift is driven by physics (higher $E_c$ and thermal conductivity), resulting in superior characteristics (faster switching, lower $R_{on}$), but introduces new reliability challenges (gate oxide stability, lower short-circuit ruggedness). Unipolar devices (e
Operation is limited by the impact ionization process, where a high electric field accelerates carriers to energies sufficient to create additional electron-hole pairs, leading to a sudden surge in current. The penalty is stored charge, causing a reverse
Reliability in power electronics is distinct from standard microelectronics due to high electric fields, high current densities, and significant self-heating. Operation is limited by the impact ionization process,