ON THE USE OF DIMERIC ANTIMONY IN MOLECULAR-BEAM EPITAXY

We have conducted studies on the use of a cracker cell for antimony ge nerating Sb-2 molecules. For GaSb/GaSb epilayers, compared with the on es produced with a traditional cell generating Sb-4 molecules, the use of the cracker cell has allowed two remarkable improvements: The most impressive one is the optical quality as displayed by photoluminescen ce at 2 K. We present in particular a spectrum with a BE4 excitonic li ne of full width at half maximum equal to 1.7 meV, which is, in our kn owledge, the best reported value in the field of MBE. The other is the higher crystallographic quality: GaSb epilayers made from Sb-4 surpri singly did not match the GaSb substrate. We showed that this mismatch could be attributed to arsenic coming from a film deposited on the sur roundings of the antimony cell during previous arsenide growth. The co ntinuous heating of the cracker tube (at a stand-by temperature of 700 degrees C) caused the sublimation and the total disappearance of the film of arsenic. Epilayers made with the ''clean'' cracker cell match the substrate and have 004 diffraction peaks with a FWHM of 12 '' whic h is the typical value given by bare substrates.