Wide band-gap materials

Although silicon is the most used material in power applications because of its low cost and its mature technology, the silicon power devices are limited in terms of electrical (in particular the well-known and recurring problem of the « on-state resistance / breakdown voltage » trade-off), thermal and thermoelectric performance. In order to answer the new requirements of energy management systems, power devices caracteristics must be strongly improved.

A possible solution to overcome these silicon power devces limits consists in changing the semiconductor: wide band-gap semiconductor materials exhibit a great opportunity for high temperature (300-700 K) and high voltage (≥ 600 V) power devices. The most promising materials are silicon carbide (SiC), gallium nitride (GaN) and diamond. Compared to silicon, the main benefits brought by these materials are a good operation over a wide range of temperature, a high critical electric field, a high velocity saturation and a high thermal conductivity.

Our research activities on gallium nitride power switches are recent. During the years 2001-2005, one could note the substantial progress but primarily limited to normally-on power devices (mainly HEMT). Thus, the semiconductor technology evolutions make it possible to consider gallium nitride as a promising material, which deserves a true R&D investment. Furthermore, contrary to silicon carbide which must obligatorily be carried out by crystalline growth on of the same substrate composition, GaN can be deposited by hetero-epitaxy on silicon substrates thus allowing a production on sections of more important surface (150 mm).

Thanks to its exceptional physical properties, diamond is the ideal material for power electronics. Some demonstrators (mainly Schottky diodes) were already realised and have shown the great potential of diamond. However current quality and layer dimensions are obstacles for the development of the diamond technology in the world. The LAAS knowledge in technology silicon help to develop basic technological steps and simulation platform for the design and realisation of high voltage and high temperature diamond power devices.

Characterisation device on P- diamond substrate (3*3mm²). SEM Photograph of etched
PIP structure
Projects in progress