A comparison of the transitory periods in GaAs and AlGaAs CBE growth

Prior to the establishment of steady-state growth for GaAs(001) and AlGaAs(001) using triethylgallium, trimethylgallium, trimethylaminealane and cracked arsine in a VG V80H chemical beam epitaxial growth system, there occurs a transitory period after the onset of precursor arrival at temperatures between 510 and 585°C and at all III:V BEP ratios. Both reflectance (R) and reflectance anisotropy (RA) spectroscopy have been used to monitor the changes over this period. The transitory period lasts for a minimum time of ∼1s for a III:V beam equivalent pressure (BEP) ratio ⩽0.25 (irrespective of temperature), with the usual RA monolayer growth oscillations at the start of steady-state growth. At higher III:V BEP ratios the duration of the transitory period increases to beyond 60s. Distinct features are observed in the RA over the transitory period, which are attributed to different surface reconstructions. A comparison of transient period duration for GaAs (TEGa and TMGa) and AlGaAs at high III:V (BEP) ratios under identical growth conditions indicates that the transient period may be determined by the relative decomposition rates of precursors. Transients are shorter for GaAs than AlGaAs, and when GaAs is grown from TMGa rather than TEGa.