Real-time control of molecular beam epitaxy by optical-based flux monitoring

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Abstract
We have developed a real-time molecular beam epitaxy control system based on Al and Ga atomic beam resonant absorption of hollow cathode lamp emission. By continuously monitoring the absorption of Al and Ga beams during growth, this system accurately determines instantaneous growth rates and then integrates these over time to determine layer thickness. This information is used in real time for effusion cell shutter (and hence layer thickness) control. The accuracy and flexibility of this system is demonstrated here by growing AlAs/GaAs distributed Bragg reflectors with consistent layer thicknesses even though effusion cell temperatures were intentionally varied. In each instance the system automatically detected and compensated for the different growth rates, resulting in DBRs with center wavelengths controlled to within 0.3% of the target wavelength.