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Semiconductor diode

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Semiconductor diode

A semiconductor device model

- The diode is the classical semiconductor device, and is mainly used as a rectifier
- From a modeling perspective the device has a well known theoretical behavior, so it often serves as a benchmark structure for device simulations
- A simple implanted diode structure have been modeled in COMSOL Multiphysics, and analyzed using stationary and transient analysis
- In particular, the electrical IV-characteristic, and the reverse recovery is studied

- The geometry is a cross-section of the diode, using depth of 1 µm of the implanted pn-junction

- The Poisson equation is coupled with the drift-diffusion equations for electrons and holes:
- Electrons and holes assume to have a Boltzmann distribution, which is an approximation for the Fermi-Dirac distribution
- Shockley-Reed-Hall recombination is present inside the semiconductor

- The mesh have to be dense near the pn-junctions and in the transition between the lowly doped and highly doped n-type regions

- The electrical IV-characteristics can be used to extract the diode’s ideality factor, on-resistance, and saturation current

- A surface plot in log scale of the hole concentration reveals that the diode has entered high-level injection at 0.2 mA forward current

- The transient simulation studies the transition from the high-level injection state at forward bias to the blocked state in reverse bias
- The diode reach a high reverse voltage with a high current, maximizing the risk of failure due to the large dissipated power