In response to requirements for alternative energy, and to overcome the theoretical limits of silicon, CEA-LETI has chosen to develop a disruptive technology based on gallium nitride. Current transistors based on GaN material are field effect transistors based on a heterostructure of III (Al, In, Ga) N / GaN, which is also referred to as a HFET (heterostructure field effect transistor). The hetero-epitaxy of GaN on 200mm silicon requires major developments to manage lattice mismatch and differential expansion coefficients between materials. We propose in this research to develop new substrates by direct bonding and thinning to facilitate the growth of these structures.The Phd student will have to understand the difficulties of epitaxial growth of heterostructures, as well as the problems induced by defectivity in the components and in terms of realization and operation.

He will start studying the implementation of innovative substrates managing all or part of the problems. This innovative substrate will be achieved through a combination of direct bonding and thinning techniques that allow the assembly of very dissimilar materials without defects (as for silicon on insulator (SOI) wafers manufactured for microelectronics).

A theoretical approach will require a search for materials that match the lattice parameter or expansion coefficient of GaN (SIC, metals etc.). Availability will be checked in 200 mm and a simulation of the behavior of these materials with temperature will be performed thanks to dedicated software such as Ansys, Comsol, Abaqus. An analysis of the published and patented worldwide works on that subject will be done by the Phd.

A draft of specifications od the “ideal substrate vs the wanted device will have to be written.” Finally the fabrication of engineered substrates will be conducted and characterized (acoustic microscopy, curvature FRT, SEM, TEM, etc …). Consideration will be given to a demonstration of epitaxial growth on these substrates, followed by physical and electrical characterization.

The Phd will have to implement these engineered substrates, developing new fabrication methods, then validating these products by performing epitaxial growth and processing these layers into electrical components. Electrical characterization will be the final judge of process improvement.

This position is open until it is filled.

Department: Département Composants Silicium (LETI)
Laboratory: Laboratoire de Substrats Avancés
Start Date: 01-10-2015
ECA Code: SL-DRT-15-0679
Contact: thomas.signamarcheix<στο>cea.fr