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Project TitleControlling Growth Rates And Compositions Of Films
Track Code11065
Short Description

Developed at McGill University, this technology describes a novel method and apparatus for controlling the growth of epitaxial films. In particular this can be applied to Molecular Beam Epitaxial (MBE) systems. These systems were developed at Bell Labs in the late 1960s to grow crystalline films on substrates. MBE systems are widely used for growing compound semiconductors such as gallium arsenide, indium phosphide, nitrides, silicon germanium and silicon carbide and the resulting devices are used in applications such as opto-electronics and monolithic microwave circuits. MBE systems require high vacuum environments to enable the molecules traveling within to migrate in straight lines and enable atomic-level deposition. The source of the material for the films is usually housed in effusion cells which generally have valves or shutters that open and shut. Controlling the deposition rate and thus the composition requires the adjustment of the temperature of the effusion cell. However this approach is not instantaneous and in an attempt to increase the rate of change of the flow rate, MBE systems have been equipped with multiple effusion cells of the same material to better control the deposition. This costly and still limited approach is helpful but is incomplete.

In an MBE’s ultra-high vacuum chamber, the atoms which travel in straight lines on their way to the sample are often collimated to direct the “beam” of atoms, and this is akin to a light source from a pinhole.  Following this analogy, this technology consists of an apparatus which acts like a beam splitter where the variation of the flux can be varied almost immediately as opposed to the current method which requires changing and stabilizing the temperature of the effusion cell to change the flux of the atoms. In addition, since the current technology uses temperature as the method to vary the flux of atoms, it is often quite hard to stabilize the beam since the flux of atoms is exponentially dependant on the temperature, therefore small variations in temperature can dramatically change the flux. This enables MBE systems to more accurately control the growth of films by accurately managing the flow rate, as well as reducing the overall manufacturing times.

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Posted DateMar 14, 2012 2:16 PM

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