EDUCATIONAL ISSUES FOR POWER SEMICONDUCTOR-DEVICES

The teaching of power semiconductor devices often requires a more deta iled presentation of the basic physical and electrical parameters than used in semiconductor device physics courses; this is true not only f or the standard power devices, like BGTs, GTOs and power MOSs, but als o for the more recent ones that merge the MOS effect with bipolar oper ation, like IGBTs, MCTs, ESTs, etc. In fact, usually in these basic co urses many important items for the power devices such as the limiting effects of breakdown, the temperature effects on transport properties, the constraints posed by the large area and low doping, the effects o f high injections and the limits imposed by high current effects, like secondary breakdown, are not considered. In this paper some of the po ints will be briefly recalled that could be considered in courses deal ing with power semiconductor devices, with the aim of suggesting a pos sible and useful link between the basic properties studied in solid st ate physics courses and the performance of modern power devices. In pa rticular, the dependence of mobility and lifetime on doping, injection level and temperature should be stressed because they play a major ro le in the electrical operation of the devices. Secondly, the basic eff ects that limit the ratings of the power devices both in steady state conditions and in the rum-on and rum-off transients must be discussed and used to understand their role in the rating of different types of devices, either unipolar, bipolar, or mixed MOS-bipolar ones. Finally, the 2D effects that act in determining some important phenomena in po wer devices should be presented both with simplified analysis and with CAD tools; these latter need to be introduced to make the student awa re of their use and possibilities.