Selective area growth of AlGaAs on GaAs by PSE/MBE

Selective area growth (SAG) of AlGaAs on GaAs (0 0 1) and GaAs (1 1 1)B substrates, patterned with a SiO2 mask, was successfully achieved by applying the new technique of periodic supply epitaxy (PSE) to molecular beam epitaxy (MBE). Complete selective growth with no formation of AlGaAs islands on the mask and a very good morphology of the epitaxial layer was obtained at a substrate temperature as low as 640 degrees C with an Al concentration up to 2% and with a mask to window area ratio even bigger than 100. Different growth conditions and different PSE parameters were studied and their influence on selectivity is shown. The grown layers were observed by Nomarski optical microscopy and by atomic force microscopy (ATM). The selectivity is possible at a relatively low growth temperature because, during the interruption time of the PSE technique, the AlGaAs islands have time to decompose and then Al and Ga adatoms coming from these decomposed islands can re-evaporate or migrate on the mask toward the window region. The effect of Al was revealed to be strong in reducing the selectivity even at very low Al concentrations due to the higher energy required to break the Al-As bonds than the Ga-As bonds.