IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Semiconductors Tuesday Sessions
       Session SC-TuA

Invited Paper SC-TuA4
Dislocations and Microstructure Evolution in Semiconductor Thin Films

Tuesday, October 30, 2001, 3:00 pm, Room 124

Session: Semiconductor Heterojunctions
Presenter: A. Sakai, Nagoya University, Japan
Correspondent: Click to Email
The utilization of high-quality heteroepitaxial films is the key to realizing high performance optoelectronic and electronic semiconductor devices. In general, a lattice mismatch between a heteroepitaxial film and a substrate induces strain into the film and the strain relaxation is achieved by the introduction of misfit dislocations. This, in most cases, results in threading dislocations in the film, which severely degrade the properties required for the device operation. In order to reduce the threading dislocation density, we have performed novel heteroepitaxy which is based on the idea that misfit dislocations are confined at the hetero interface regions without leaving their threading arms in the film. Two successful demonstrations for GaN and SiGe thin films are presented. 1) Facet-initiated epitaxial lateral overgrowth (FIELO) allows us to obtain GaN films on sapphire substrates with threading dislocation densities on the order of 10@super 7@ cm@super -2@ which is two orders of magnitude smaller than that of the conventional epitaxy. Transmission electron microscopy analyses revealed that the reduction of the threading dislocation density was mainly due to dislocation bending in the FIELO GaN layer. Mechanisms of dislocation propagation which is closely related to the appearance of the facets early in ELO are discussed. 2) Strain-relaxed SiGe buffer layers on Si(001) substrates with low threading dislocation densities have been grown. The process consists of annealing of the first low-temperature-grown SiGe layer and growth of the second SiGe layer on the first layer. A thin capping Si layer formed before the annealing effectively suppressed surface roughening during the annealing. Periodic undulation was formed on the second layer surface, conformably to the alignment of interface misfit dislocations. This undulation plays an important role in introducing the dislocations uniformly and in suppressing the entanglement of threading arms of the dislocations.