MEASUREMENT AND CONTROL OF REAGENT CONCENTRATIONS IN MOCVD REACTOR USING ULTRASONICS

An ultrasonic cell for monitoring gas mixtures on MOCVD reactors has been developed from being a laboratory instrument to a standard, rack-mounted, system which interacts with the reactor's computer, and is marketed under the trade name of EPISON. A feedback circuit has been implemented to stabilize the TMI mole fraction in the reactor. The effectiveness of the feedback circuit has been tested by growing InGaAs layers, during which the TMI concentration was deliberately perturbed by changing the pressure of the TMI line. Using feedback correction an X-ray rocking-curve peak with a FWHM of 25 arc sec was obtained for a layer grown with the same perturbations which had previously led to a 400 arc sec FWHM without feedback.