Superjunction Devices - Akshay K - Bog

Devices for generation, distribution and regulation of electric power are important parts of appliances for healthcare, comfort, defence and transportation. Two classes of such devices discussed in this thesis are diodes and MOSFETs. These are used in rectification, amplification and switching applications, and are realized in semiconductor materials. The power level at which these devices operate is decided by the application. Depending on the voltage and current rating, this can vary from 1 Giga Watt at the power station to few Watts for mobile chargers. To cater to this wide range of power levels, power converter circuits are often employed. Depending on the application, these converters could be AC-DC, DC-AC, DC-DC or AC-AC. Although the functionality of these circuits is different, all of them invariably requires power switches. The performance of these switches decides the conversion efficiency of the converter.

So far, power devices fabricated in Si (silicon) have been the workhorse. It is of interest to discuss the performance of a Si switch in terms of the five characteristics listed above. Silicon switches are mostly normally off and thereby avoid complex driving circuits. Apart from this, Si switches underperform in terms of the other four characteristics.

Superjunction concept was originally introduced in the context of silicon devices. Later, it has been extended to other wide bandgap materials like SiC and GaN to combine the advantage of linear VBR-RONSP relation and the large value of EC.

It is to be noted that although different materials offer different technological challenges to realize a superjunction, the theory of superjunction operation and the analytical design equations are valid across materials upon making changes to the material specific parameters (e.g. impact ionization coefficients, mobility etc.). Hence, a model developed to design the optimum superjunction parameters has potentially a large impact. It can help technologists working across materials to steer their efforts more effectively towards realizing the best device for a target application with minimum cost and effort.