The growth of Si-doped liquid-encapsulated Czochralski material exhibited a significant deviation, in Si incorporation, from that which was predicted by a classical segregation model. It was usually expected that, for a given impurity segregation coefficient, dopant incorporation throughout the crystal could be calculated with fairly good accuracy. Profiles for Te-doped liquid-encapsulated Czochralski material gave a close approximation to this classical model. However, in the case of Si-doped material, the dopant distribution in the crystals deviated significantly from the segregation model. In some cases, this deviation amounted to several orders of magnitude. The degree of deviation was found to depend upon the growth conditions. The present work was performed in order to understand the source of the deviation from the model and to permit accurate account to be taken of Si incorporation. Therefore, Si-doped crystals were grown by using a low-pressure liquid-encapsulated Czochralski technique and were intended to be doped with between 1016 and 1018/cm3. The actual dopant incorporation was significantly lower than that predicted by the segregation model, and the axial dopant variation was much too flat. Also, in spite of the use of intentional Si doping, a significant number of the crystals was semi-insulating. An analysis of the experimental data showed that this doping behavior could not be explained by assuming the existence of an unknown compensating impurity. A different model was developed which was consistent with all of the observations and which provided an accurate account of Si incorporation. An understanding of the Si incorporation anomaly permitted successful process changes and improvements to be made. This model explained the observed anomaly by taking account of Si diffusion between the GaAs melt and the B2O3 encapsulant, as well as of permanent Si trapping in the B2O3. When the interaction of Si with B2O3 was taken into account, the Si incorporation obeyed the segregation model and the anomaly vanished.

A.Flat: Journal of Crystal Growth, 1991, 109[1-4], 224-7