In situ Al2O3 atomic layer deposition on pristine (0 0 1) GaAs: interface chemistry and its implication on charge carrier recombination and Fermi level pinning

• Al 2 O 3 /GaAs interface formed by in situ atomic layer deposition of Al 2 O 3 on (0 0 1) GaAs. • Characterization with X-ray photoelectron spectroscopy and photoluminescence (300 K) • (0 0 1)GaAs effective passivation: growth on Ga-terminated GaAs, Al 2 O 3 thickness > 3 nm. • PL intensity is significantly (x20) higher than that of unpassivated GaAs. • Reduction of band bending in GaAs at the Al 2 O 3 /GaAs interface by 0.2–0.4 eV. The study investigates the Al 2 O 3 /GaAs interface formed by in situ atomic layer deposition (ALD) of Al 2 O 3 on pristine (0 0 1)-oriented GaAs substrate, using X-ray photoelectron spectroscopy (XPS) and room-temperature photoluminescence (PL). The Al 2 O 3 /GaAs interface is free of high-valence arsenic (As 2 O 3 and As 2 O 5 ) and gallium (Ga 2 O 3 ) oxides when the Al 2 O 3 layer thickness exceeds 3 nm. The Al 2 O 3 deposition on an As-terminated GaAs substrate leads to the presence of low-valence arsenic oxides (As 2 O and AsO) and As–As bonds related to As–As dimers at the interface. These dimers restrict the PL enhancement to approximately twice that of unpassivated GaAs. In contrast, Ga-terminated GaAs exhibits a reduction of roughly an order of magnitude in these interfacial species, as well as a PL intensity that is significantly (x20) higher than that of unpassivated GaAs. When the Al 2 O 3 layer thickness is less than 3 nm, both the low- and high-valence oxides, as well as elemental As, are detected in the near-interface region of Ga- and As-terminated GaAs samples. The PL intensity of GaAs capped with an Al 2 O 3 layer thinner than 3 nm is still considerably (x8) higher than that of unpassivated GaAs and is mainly limited by elemental arsenic. According to XPS data, oxide deposition reduces band bending in GaAs at the Al 2 O 3 /GaAs interface by 0.2–0.4 eV, indicating a decrease in interface state density, i.e. the unpinned state of the Fermi level at the interface. The study delivers criteria for the high-quality passivation of (0 0 1) GaAs surface.