IODINE-ASSISTED MOLECULAR-BEAM EPITAXY

Iodine was introduced into our solid source molecular beam epitaxy cha mber during the growth of GaAs and AlGaAs layers and strained-layer In GaAs quantum wells. Photoluminescence spectra of these samples taken a t 4.2 K were compared to spectra from a series of test samples which w ere grown in the absence of iodine flux, We have observed a general im provement of the material quality of AlGaAs layers grown at substrate temperatures around and below 600 degrees C since the introduction of iodine into our chamber regardless of whether an iodine flux impinged on the substrate during the growth process or not. Strong excitonic pe aks with full width at half maximum of only 8 meV were observed in 4.2 K photoluminescence spectra of undoped Al0.2Ga0.8As layers grown at s ubstrate temperatures as low as 550 degrees C using As-4. The epitaxia l layers grown since the introduction of iodine are the brightest Al0. 2Ga0.8As samples that we have obtained from our molecular beam epitaxy system. These results suggest that the presence of iodine in a molecu lar beam epitaxy system can result in improved optical properties for AlGaAs. The 4.2 K photoluminescence spectra and secondary ion mass spe ctroscopy depth profiles also show that iodine preferentially removes Ga from AlGaAs layers during growth, resulting in layers with higher A l content.