Ijaz Jafri

Role of crucible partition in improving Czochralski melt conditions

Many of the inhomogeneities and defects in the crystal grown from a pool of melt are because of the inherent unsteady growth kinetics and flow instabilities of the process. A scaled up version of the Czochralski process induces oscillatory and turbulent conditions in the melt, thereby resulting in the production of non-uniform silicon crystals. This numerical study reveals that a crucible partition shorter than the melt height can significantly improve the melt conditions. The obstruction at the bottom of the crucible is helpful but the variations in heat flux and flow patterns remain random. However, when the obstruction is introduced at the top of the melt, the flow conditions become much more desirable and oscillations are greatly suppressed. It is also found that a full-melt height partition or a double-crucible may not be a good choice. An optimal size of the blockage and its location to produce the most desirable process conditions will depend on the growth parameters including the melt height and the crucible diameter. These findings should be particularly useful in designing a solid polysilicon pellets-feed continuous Czochralski process for Si crystals.

A new high-pressure system for synthesis and crystal growth of large diameter InP

An advanced high-pressure crystal growth system for one-step synthesis and growth has been constructed from a design based on numerical simulations and experiments. Experimental work reported previously, optimizing the one-step in-situ process for synthesis and growth, served as a basis for developing the new furnace. A global model developed to simulate growth conditions in the prototype system, has contributed to our understanding of complex transport phenomena such as thermoelastic strain and dopant incorporation. Using both the experimental and the simulation results, we have designed a system to produce large diameter, high purity, low defect density compound semiconductor crystals at low cost.