HIGH-RESOLUTION X-RAY-ANALYSIS OF STRAIN IN LOW-TEMPERATURE GAAS

X-ray-diffraction measurements have been used to characterize GaAs lay ers grown at low temperature on GaAs substrates by molecular-beam epit axy. Three ranges of low-temperature growth are defined, labeled as '' low range,'' (less than 260-degrees-C), ''midrange,'' (between 260 and 450-degrees-C), and ''high range,'' (above 450-degrees-C), as measure d by a growth-chamber thermocouple. Films grown in the low range are a morphous, those in the midrange are fully strained and lattice matched to the substrate, and those grown above 450-degrees-C are similar to ordinary GaAs. A notable property of the midrange layers is the expans ion and contraction of the lattice parameter with thermal anneals up t o 900-degrees-C. From x-ray rocking-curve measurements on more than 20 0 anneal conditions in this group, a growth model based on arsenic ant isite defects is proposed.