| 摘要 |
A method and system for controlling the introduction of a species according to a determined concentration profile of a film comprising the species introduced on a substrate. In one aspect, the method comprises controlling the flow rate of a species according to a determined concentration profile of a film introduced on a substrate, and introducing a film on a substrate, the film comprising the species at a first concentration at a first point in the film and a second concentration different than the first concentration at a second point in the film. Also, a bipolar transistor including a collector layer of a first conductivity type, a base layer of a second conductivity type forming a first junction with the collector layer, and an emitter layer of the first conductivity type forming a second junction with the base layer. An electrode configured to direct carriers through the emitter layer to the base layer and into the collector layer is also included. In one embodiment, at least one of the first junction and the second junction is between different semiconductor materials to form at least one heterojunction. The heterojunction has a concentration profile of a semiconductor material such that an electric field changes in an opposite way to that of a mobility change.
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