GaN-based devices (LEDs, LDs, HEMTs, ...), usually grown on sapphire or silicon carbide substrates, have now a large impact on semiconductor industry development. The growth of device-quality GaN-based heterostructures on silicon substrates would be of huge importance in terms of cost, availability, processing and integration. This is the reason why more and more fundamental as well as industrial research groups are now involved in the development of GaN epitaxial growth on silicon substrates. In contrast to classical III-V compounds like GaAs and InP, GaN-based devices are well known for their exceptional material robustness as illustrated by their very good characteristics despite the presence of high dislocation densities. Therefore, in case of a successful growth of GaN on silicon, GaN-based electronics and optoelectronics as well as the integration of Si- and GaN-based devices on the same chip becomes feasible.

To achieve high-quality GaN-based epitaxial films on silicon substrates, a specific growth process must be developed in order to overcome several difficulties: - the silicon surface is very reactive to both, group III elements and nitrogen related species used during the growth, -the large lattice mismatch produces a huge amount of dislocations, - the large difference in the thermal expansion coefficient introduces an important tensile stress in GaN-based epitaxial layers. By using Molecular Beam Epitaxy and ammonia as the nitrogen precursor, a process was developed for the growth of device-quality GaN layers on silicon (111) substrates. This growth process which has been proven very efficient in terms of epitaxial relationship, polarity control, dislocation density reduction, quality of surfaces and interfaces and tensile strain compensation, will be discussed. In particular, details about the AlN nucleation conditions and the buffer layer stacking which are found to be key parameters will be presented. Structural, optical and electrical properties of GaN films and heterostructures will be discussed and device results [1-3] obtained in collaboration with partners will be shown.

[1]. Observation of rabi splitting in a bulk GaN microcavity grown on silicon N. Antoine-Vincent et al., Phys. Rev. B 68, 153313 (2003)

[2]. AlGaN/GaN HEMTs on Si(111) with 6.6 W/mm output power density R. Behtash et al., Electronics Letters. 39, 626 (2003)

[3]. Microcavity light emitting diodes based on GaN membranes grown by molecular beam epitaxy on silicon J.-Y. Duboz et al., Jpn. J. Appl. Phys. 42, 118 (2003)

Recently, Nitride semiconductors, such as GaN, AlN and AlGaN, have attracted much attention aiming at high-frequency and high-power electronic devices as well as optoelectronic devices. The major growth technique for these applications has been metalorganic chemical vapor deposition (MOCVD). On the other hand, molecular bean epitaxy (MBE), which is well-known to be another advanced technology for semiconductor thin film growth, has been behind MOCVD for the growth of nitrides, because of the poor quality of the grown films.

However, for these several years, various kinds of compact plasma sources have been developed as a N source, and the understanding of the growth mechanism has been much advanced. We have clarified the importance of lattice polarity for the growth of nitrides by MBE, and achieved the drastic improvement of film quality, which enabled us the fabrication of high-frequency heterojunction field effect transistor (HFET) by using MBE-grown nitride films.

In this talk, I will reviewed the present status of MBE technique for nitride film growth, and their application to electron devices, including our recent results related with structure characterization and device fabrication.