In situ anti-oxidation treatment in GaAs MOVPE by as desorption and passivation with AlP

In situ anti-oxidation treatment after the growth of GaAs is essential for an ideal interface between GaAs and an Al2O3 gate dielectric, because the arsenic oxide is a major origin of interface states. The growth of AlP epitaxial layer on the top of GaAs was proposed as a novel anti-oxidation passivation method. The AlP layer almost converted to Al2O3 upon air exposure, serving as both a stable anti-oxidation layer and as part of a gate dielectric. Compared with surface passivation with Al by exposure to TMAl (trimethylaluminum), which we have proposed previously, the morphology of the passivated surface, which is a critical factor for the performance of a metal-insulator-semiconductor (MIS) structure, was dramatically improved due to the coexistence of a group-V precursor. For an ideal interface without arsenic oxide, an arsenic-free surface prior to the AlP growth was also required. H2S treatment allowed us to obtain the low-As-content c(8×2) surface reconstruction of GaAs for the first time by MOVPE. Passivation by AlP on the low-As-content c(8×2) surface reconstruction of GaAs has made it possible to obtain an Al2O3/GaAs gate stack which exhibited smooth morphology and complete suppression of arsenic oxide. Reduction of interface states by this passivation was evidenced by the improved photoluminescence intensity from GaAs.