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Several issues have to be carefully included in the numerical models for the simulation of power semiconductor devices. Due to the high-voltage and (or) high-current operation, interaction of electrical and thermal phenomena is important. Therefore, the heat-transport equation has to be solved simultaneously with the semiconductor equations to estimate the thermal behavior. Accurate impact ionization models are also important to see high-voltage operations of power devices.
For bipolar power devices multi-recombination levels cannot be neglected. Several of the commercial high-power bipolar devices have multi-traps in the energy band gap for the purpose of fast carrier recombination during turn-off. Practically an empirical model is used to treat the doping and temperature dependence of carrier lifetime. Hot carrier effects are not so important for vertical power devices. However, for the CMOS compatible lateral power devices, it is one of the critical factors. Currently, semi-classical and quantum effects can be neglected in power devices. However, as the technology improves, these effects will become more important especially for lateral power devices for smart power applications.
Numerical device simulation is widely used to optimize device characteristics and to study carrier transport in semiconductor devices. It allows detailed analysis of mechanisms involved in device operation. In power semiconductors there is a trade-off between the breakdown voltage and on-resistance. With the help of numerical simulation these two characteristics can be optimized by a proper choice of structure parameters. To suppress the latch-up of the devices (mainly CMOS near the lateral power devices or power device itself) the substrate current of lateral power devices must be kept small. Generally, the amount of the substrate current is related to the location and values of impact ionization. Another important role of numerical simulation is to establish new device concepts.