ON THE USE OF DIMERIC ANTIMONY IN MOLECULAR-BEAM EPITAXY

We have conducted studies on the use of a cracker cell for antimony generating Sb-2 molecules. For GaSb/GaSb epilayers, compared with the ones 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 photoluminescence at 2 K. We present in particular a spectrum with a BE4 excitonic line of full width at half maximum equal to 1.7 meV, which is, in our knowledge, the best reported value in the field of MBE. The other is the higher crystallographic quality: GaSb epilayers made from Sb-4 surprisingly did not match the GaSb substrate. We showed that this mismatch could be attributed to arsenic coming from a film deposited on the surroundings of the antimony cell during previous arsenide growth. The continuous 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 '' which is the typical value given by bare substrates.