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Using a combination of scanning tunneling microscopy (STM) and spectroscopy with density functional theory calculations, the electronic properties of the subsurface arsenic antisite defect (AsGa) are unambiguously delineated from those of the surrounding As atoms in undoped gallium arsenide (GaAs) lattice with atomic precision. In the GaAs(110) surface with AsGa located at the second layer (2‐AsGa), it is found that the midgap state induced by 2‐AsGa manifests as a bright contrast at the AsGaAs bond site. Furthermore, it is shown that STM images taken at large magnitudes of negative sample bias are dominated by the local density of states of neighboring surface As atoms. These states lead to a four‐lobe symmetric contrast in the filled‐state STM image around the 2‐AsGa defect. These results provide insights for surface/subsurface defect engineering at the atomic scale. [ABSTRACT FROM AUTHOR]

The deposition of n-GaAs cap on low-temperature GaAs (LT-GaAs) improved the THz emission of LT-GaAs grown at a much lower temperature (< 300∘C), where the defect density is high, without compromising the spectral bandwidth and carrier lifetimes necessary for ultrafast THz detection. The LT-GaAs grown at 220 and 270∘C showed a 192 and 10% enhancement THz emission peak-to-peak intensity, respectively, while the sample grown at 310∘C showed a 49% reduction. The n-GaAs cap reduced the As-related defects density in the LT-GaAs resulting to improved THz emission. The THz emission from the sample grown at 310∘C with already low defect density suffered possibly due to the free carrier absorption by the n-GaAs cap. The results are relevant in future material design of LT-GaAs based photoconductive antenna. [ABSTRACT FROM AUTHOR]

We report on the shell-to-core carrier-transfer in GaAs/Al0.1Ga0.9As core-shell nanowires grown on Si(1 0 0) substrates via molecular beam epitaxy. The nanowires are dominantly zincblende and are tilted with respect to the substrate surface. Photoluminescence (PL) excitation spectrosocopy at 77 K revealed an abrupt increase in the GaAs PL intensity at excitation above the Al0.1Ga0.9As shell bandgap which is attributed to shell to core carrier-transfer. More carriers from the Al0.1Ga0.9As transfer to the GaAs at T>90 K, as observed in the time-resolved PL and temperature dependence of the relative PL intensities of GaAs and Al0.1Ga0.9As due to the ionization of the traps within the Al0.1Ga0.9As. Using a coupled rate equation model that takes into account shell to core carrier-transfer, the average recombination time constants of Al0.1Ga0.9As shell τrec,s=400 ps (580 ps) and GaAs core τrec,c=600 ps (970 ps) were obtained from the time-resolved PL at 300 K (77 K). Carrier-transfer time constants τCT=50 ps (55 ps) at 300 K (77 K) were also obtained. [ABSTRACT FROM AUTHOR]

We report short carrier lifetimes for GaAs/AlGaAs isolated single quantum wells (35, 50, and 90Å) grown via molecular beam epitaxy at 630°C. Photoluminescence (PL) measured at 14–150K show defect transitions that significantly thermalize at ~77K. Carrier lifetimes of the quantum wells, measured via time-resolved PL (TRPL), are ~21ps (35Å), ~39ps (50Å) and ~48ps (90Å). Carrier lifetimes and fluence-dependence measurements suggest that at 77K where the shallow levels have thermalized, deeper level defects are still present and act as effective carrier traps. The defect density appears to vary inversely with well-width, and this observed behavior is explained on the basis of interface roughness. [ABSTRACT FROM AUTHOR]

• The third layer As-antisite defect in GaAs(1 1 0) mimics that of bulk GaAs. • STM image from experiment and theory present a unique asymmetric two-lobe contrast. • Calculated LDOS and STS spectra reveal three prominent peaks as surface signatures. We reveal the As-antisite (As Ga) defect close to the surface of GaAs(1 1 0) with bulk characteristics using first-principles methods with experimental verifications. We found that the As Ga in the third-layer mimics the geometry, partial charge density and more importantly, the density of states of As Ga in bulk GaAs. Notably, the mid-gap state induced by As Ga in bulk GaAs is well-reproduced by the As Ga in the third layer of GaAs(1 1 0). Simulated and experimental STM images show an "asymmetric two-lobe" feature in the region around the defect. Using local density of states (LDOS) and STS spectra, we propose three prominent peaks with characteristic energy levels corresponding to the third layer As Ga. The above results present the first report of surface electronic signatures of true bulk defect near the surface of GaAs(1 1 0). [ABSTRACT FROM AUTHOR]