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

We report on the implementation of technique of desorption mass spectr ometry (DMS) in a real-time feedback loop for continuous monitoring an d control of layer composition during molecular beam epitaxy growth of AlGaAs on (001) GaAs at high substrate temperatures. With this techni que, the Ga desorption rate F(d)(Ga) and thus the composition is monit ored continuously and kept at the desired value by adjusting either th e substrate heater power or the incident arsenic flux. Composition con trol 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 photol uminescence (PL) results. The ability to produce complex graded struct ures by DMS control is demonstrated by the growth of nominally parabol ic 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.