Nonlinear feedback control and observer design for the modern effusion cell

In the molecular-beam epitaxy (MBE) process precise control over thickness, composition, and doping profiles are critical for end device performance. This paper addresses the problem of accurately controlling the flux sources (effusion cells) used in MBE. We present a nonlinear compensator based on exact input-output linearization via feedback to control the flux of an effusion cell. The unmeasured states, necessary for implementation of the controller, are estimated by a Kalman-Bucy observer. We present simulations of the composite observer/nonlinear controller system, showing successful flux command following and elimination of shutter induced flux transients.