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

X-ray-diffraction measurements have been used to characterize GaAs layers grown at low temperature on GaAs substrates by molecular-beam epitaxy. 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 measured by a growth-chamber thermocouple. Films grown in the low range are amorphous, 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 expansion and contraction of the lattice parameter with thermal anneals up to 900-degrees-C. From x-ray rocking-curve measurements on more than 200 anneal conditions in this group, a growth model based on arsenic antisite defects is proposed.