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Theoretical Physics
Oxygen defects in Silicon

1. Why do we study Oxygen in Silicon?

The problem of oxygen impurities in silicon is one that has plagued the semiconductor industry for decades. Oxygen is the most common impurity in silicon, and can be introduced in many different ways. At high temperatures it forms aggregates or clusters within the silicon, as well as interstitial dislocation loops. These all disrupt the lattice and lead to defect states in the silicon. At lower temperatures oxygen can still be a problem, for example through the formation of thermal donors which occur when silicon is annealed at temperatures of around 450 degrees celsius. These defects are electrically active (double donors), and act as electron / hole recombination centres, lowering the mobility, etc. For this reason, it is essential to understand exactly how oxygen behaves in silicon. A full understanding of the bonding and structure, as well as the diffusion and kinetics of oxygen, will allow silicon manufacturers to optimise their manufacturing processes in order to minimise the oxygen problem. This in turn should lead to faster, cheaper, and more efficient microchip technology.

Despite the large amount of research that has been conducted in this area, remarkably little is known about the microscopic behaviour of these defects. Thermal donors were first discovered over 40 years ago, yet there is still a lot of debate about their structure, with no firm conclusions yet. Indeed, there is even controversy about the number of atoms that they contain.

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