DESORPTION MASS-SPECTROMETRIC CONTROL OF COMPOSITION DURING MBE GROWTH OF ALGAAS

We report on the implementation of technique of desorption mass spectrometry (DMS) in a real-time feedback loop for continuous monitoring and control of layer composition during molecular beam epitaxy growth of AlGaAs on (001) GaAs at high substrate temperatures. With this technique, the Ga desorption rate F(d)(Ga) and thus the composition is monitored continuously and kept at the desired value by adjusting either the substrate heater power or the incident arsenic flux. Composition control by DMS during growth of nominally constant composition layers is found to be superior to that obtained with conventional MBE growth, as indicated by F(d)(Ga) versus time profiles and low temperature photoluminescence (PL) results. The ability to produce complex graded structures by DMS control is demonstrated by the growth of nominally parabolic AlGaAs quantum wells, for which photoreflectance and PL results are consistent with the desired structure. The technique is quite general and applicable to many different compounds.