Papers by Author: M. Ucar

Abstract: The development of the Continuous Feed Physical Vapour Transport (CF-PVT) process requires a perfect control of each phenomenon in the growth cell. Along this line, the present paper gives some inputs on the CF-PVT mass transfer regimes with respect to the process parameters, both from qualitative and quantitative viewpoints. For example, two boundary cases have been evidenced depending on the temperature. At low temperature, the growth is limited by the sublimation step between the source and the seed. In this case, the CF-PVT process can be roughly assimilated to the classical seeded sublimation technique. At high temperature, the process is limited by the feeding step, i.e. the CVD deposition and infiltration on the lower part of the source. Measurements are correlated to in-situ X-ray imaging. The ability of the X-ray imaging to in-situ qualify and quantify the mass transfer is discussed.

Abstract: Thick (111) oriented β-SiC layers have been grown by hetero-epitaxy on a (0001) a-SiC substrate with the Continuous Feed-Physical Vapour Transport (CF-PVT) method. The growth rate was 68 µm/h at a pressure of 2 torr and a temperature of 1950°C. The nucleation step of the β-SiC layer during the heating up of the process was studied in order to manage first the a to b heteropolytypic transition and second the selection of the b-SiC orientation. With a adapted seeding stage, we grew a 0.4mm thick layer almost free of Double Positioning Boundaries on a 30mm diameter sample. First observations of the layer by cross-polarised optical Microscopy are presented both in planar view and in cross section geometry.

Abstract: Modeling and simulation of the SiC growth process is sufficiently mature to be used as a training tool for engineers as well as a decision making tool, e.g. when building new process equipment or up-scaling old ones. It is possible to simulate accurately temperature and deposition distributions, as well as doping. The key of success would be the combined use of simulation, experiments and characterization in a "daily interaction". The main limitation in SiC growth modeling is the accurate knowledge of physical, thermal, radiative, chemical and electrical data for the different components of the reactor. This is the weakest link in developing completely predictive models. In addition, the link between the thermochemical history of the grown material and its structure and defects still needs further development and input of experimental data.