The Structure of Al/GaAs Interfaces (original) (raw)
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Atomic interdiffusion at Au-GaAs interfaces studied with Al interlayers
Physical Review B, 1981
We have used soft-x-ray photoemission spectroscopy at Au/GaAs interfaces to determine the movement of Au, Ga, and As atoms during the initial stages of Schottky-barrier formation. Studies of core-level features obtained with a range of photon energies between 80 and 250 eV indicate that, at room temperature, Au atoms first diffuse into GaAs, followed by the nonstoichiometric outdiffusion of Ga and As into Au overlayers. Thin Au overlayers on GaAs promote a spatial distribution of dissociated Ga and As which depends on the overlayer thickness, These microscopic phenomena result in a local charge redistribution which determines the electronic properties of the macroscopic Au/GaAs junction. We discuss the application of Al atoms at the intimate metal-semiconductor interface either as immobile markers to establish the absolute motion of interface species on an atomic scale or as indicators of the overall interface motion.
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1996
We investigated the initial stages of growth of Al films fabricated by chemical vapor deposition at 100 °C on GaAs(001)2×4 surfaces using the molecular precursor dimethylethylamine alane. In situ reflection high energy electron diffraction and scanning tunneling microscopy and spectroscopy, as well as ex situ atomic and lateral force microscopy, were employed for morphological analysis. Film growth was found to occur in the Volmer–Weber mode and involve islands with remarkably low z-aspect ratio (∼1:16). Scanning tunneling spectroscopy data on some of these islands in the early stages of growth suggest the formation of an AlAs interface phase.
Applied Physics Letters, 2010
In situ deposition of Al 2 O 3 on GaAs was performed by chemical-vapor-deposition ͑CVD͒ with trimethyaluminum and isopropanol as precursors. A gallium-rich region in the Al 2 O 3 thin film above the interface was spontaneously formed via the in situ CVD process. Ga-enrichment of the interface was observed using secondary ion mass spectrometry ͑SIMS͒ depth profile measurement. X-ray photoelectron spectroscopy ͑XPS͒ results show that the gallium-rich region consists of Al 2 O 3 and Ga 2 O 3 , but no As 2 O 3 was observed. The Ga 2 O 3-Al 2 O 3 layer above the oxide/GaAs interface reduces the frequency dispersion as measured with capacitance-voltage ͑C-V͒ characteristics and lowers the interfacial state density as compared to atomic-layer-deposition *͑ALD͒ deposited films which do not display this gallium enrichment above the interface.
Summary Abstract: Experiments on ultrathin Al overlayers on GaAs(110)
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 1983
We investigated the adatom states for different AI coverages ofInP(110) by synchrotron-radiation photoemission, including ultralow coverages below 0.2 monolayer. The adatom states below 0.1 monolayer and above-3 monolayer appear similar to the corresponding Al-adatom states on GaAs(110). In particular, the results for both systems appear consistent with the formation of Al clusters at 0.1-2 monolayer coverage, and the Fermi-level pinning occurs when the cluster formation starts. However, the similarity between the two systems is limited at intermediate (0.1-2 monolayer) coverages. At those coverages we observe a new bonded state for Ai on InP, which is not observed on GaAs. Our results emphasize, in general, the need to extend the experiments to ultralow coverages when studying the Schottky barrier formation process.
Journal of Applied Physics, 1997
We have investigated the structural and defect characteristics of GaAs and Al x Ga 1Ϫx As grown at low substrate temperature ͑250°C͒ by molecular beam epitaxy. Using x-ray diffraction we have observed an increase in lattice parameter for all as-grown layers, with the Al x Ga 1Ϫx As layers showing a smaller expansion than the GaAs layer. However, infrared absorbtion measurements revealed that the concentration of neutral arsenic antisite defect, ͓As Ga ͔ 0 , was not significantly affected by aluminum content (x), with only a small reduction for xϭ0.36. Positron beam studies showed that the low temperature layers had a higher concentration of vacancy-related defects ͑ϳ10 17 cm Ϫ3 ͒ than the semi-insulating substrate, with the Al x Ga 1Ϫx As layers having the highest values. After annealing ͑600°C, 15 min͒ the lattice constants relaxed to those of conventionally grown material and ͓As Ga ͔ 0 was reduced in all cases, with the smallest reduction occurring for the xϭ0.36 layer, indicating that the Al atoms strengthen the lattice against excess arsenic incorporation and hold the arsenic antisite atoms more strongly in position. X-ray photoelectron spectroscopy showed that arsenic diffused out of the surface region and was replaced by oxygen, possibly due to an insufficient overpressure of forming gas during the anneal. This oxygen penetration was greater for the GaAs layer than for the Al x Ga 1Ϫx As layers. Extra Raman peaks at 200 and 257 cm Ϫ1 confirmed that the surface was very disordered. There was, nevertheless, a large increase ͑4%͒ in the positron S parameter in the bulk of the annealed layers, suggesting the formation of vacancy clusters, whereas in the surface region we find evidence that As Ga diffusion proceeded at a faster rate in the xϭ0.36 than the xϭ0.2, in agreement with the vacancy-enhanced As Ga diffusion model.
Free surfaces and multilayer interfaces in the GaAs/AlAs system
Journal of Crystal Growth, 1987
Semiempirical potential energy functions have been utilized for a variety of calculations in the_Ga-Al-As system: (1) surface energies have been calculated for several orientations of GaAs; (2) ledge energies for the GaAs(001) (As terminated) surface show long range interaction effects with the ledge energy increasing with spacing; (3) GaAs(001)/A1As(001) superlattices have been simulated for a range of interlayer spacings with the excess interfacial energy per interlayer increasing from 5 erg/cm 2 at an interlayer spacing of I molecular layer (5.8 A) to 50 erg/cm2 at an interlayer spacing of 18 molecular layers (103.8 A).
Molecular beam epitaxy growth of AlGaAs on the (631)-oriented GaAs substrates
Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures, 2008
The authors report the molecular beam epitaxy growth and characterization of AlGaAs/ GaAs͑631͒ heterostructures grown at different As 4 molecular beam equivalent pressures. The reflection high-energy electron diffraction patterns taken along the ͓−1 2 0͔ azimuth showed that the twofold reconstruction commonly observed during the GaAs-buffer layer growth is preserved during the AlGaAs deposition. The 10 K photoluminiscence ͑PL͒ characterization of the samples showed transitions related to the AlGaAs band edge, the incorporation of impurities, and deep centers. The temperature dependence of the band to band PL transition was fitted with the models developed by Varshni, Pässler, and Viña. The intensity of the PL spectra drastically decreases as the As 4 pressure is increased. Photoreflectance ͑PR͒ spectroscopy also showed the best crystal quality for the sample grown at low As pressure. The authors obtained the built-in internal electric field strength and the band-gap energy from an analysis of the PR spectra close to the GaAs band edge employing the Franz-Keldysh model.