| Abstract |
Silicon as a semiconductor material is well established and first choice for the vast majority of devices. However, due to continuous device optimisation and improvements in the production process, the material properties are more and more the limiting factor. Workarounds like the super junction stretch the limits but usually at substantial cost. So a lot of effort is spent into the more straight forward approach, i.e. changing the semiconductor material. For power devices, wide band-gap semiconductors are most attractive because of low conduction and switching losses, high temperature capability, and high thermal conductivity. Despite some material and process issues back then, the first wide band-gap device, a silicon carbide Schottky-diode, was commercialised eight years ago and found a reasonable market niche. In the meantime significant progress has been made in terms of material quality and cost. However, the silicon carbide Schottky-diode is still the only wide band-gap device on the market and, in particular, there is no wide band-gap switch commercially available yet. Of course, the material cost is still two orders of magnitude higher than for silicon and there are still some material defects that lead to degradation of bipolar devices, but in general the material quality and wafer size is no longer a road block on the way to commercialisation of further devices and the device concepts are there also. So it became rather an economical than a technological question – and silicon is a strong competitor, as the case of the super junction MOSFET shows. On the other hand silicon is not just a competitor but also a strong ally, when it comes to the development of packaging suited for higher operation temperatures, frequencies, and switching speeds. So at the end the question remains: Which additional wide band-gap devices will be able to find and sustain their respective market positions. |
